CMRR

Le 28/04/2020 à 17:56, jlarkin@highlandsniptechnology.com a Êcrit :
On Tue, 28 Apr 2020 13:37:56 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 23:10, John Larkin a Êcrit :
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a Êcrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin@highlandsniptechnology.com a Êcrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Please John,

Any comments on my Analog Front End for measuring Mains Voltage/Current
(for a Energy Meter Class 0.2/0.2S) is welcomed ... if you have any time
for.

https://cjoint.com/doc/20_04/JDClKdWiT8b_Measurements-Measurements.pdf

Thanks, H




Same comment as for the GFD sensor: you are floating what could be
nice low-impedance signals to make them differential, creating a big
common-mode signal, then needing a super differential amp to remove
the common mode.

Why not hang one end of the current and potential sensors on neutral?
I referenced my entire circuit to neutral and had no differential
signals.

See TI data sheet fig 10.2. Minimize or kill common-mode signal before
trying to reject it. Even TI is doing it the hard way.
Click to expand...

In that topology Fig. 102 one shall supply an external -2V5 voltage rail
to AVSS with AVDD=2V5 This is probably a clean manner but I prefer avoid
to design a symmetrical power supply +2V5/-2V5.

Mine is enabling the internal charge pump with AVDD=3V3, Please see Fig.
105 the one named "Input swings below ground, charge pump is enabled."

 
On Tuesday, 28 April 2020 16:56:54 UTC+1, jla...@highlandsniptechnology.com
Why not hang one end of the current and potential sensors on neutral?
I referenced my entire circuit to neutral and had no differential
signals.
Click to expand...

That might get interesting if the meters get used on 3-phase supplies.

John
 
On Tue, 28 Apr 2020 11:10:12 -0700 (PDT), jrwalliker@gmail.com wrote:

On Tuesday, 28 April 2020 16:56:54 UTC+1, jla...@highlandsniptechnology.com
Why not hang one end of the current and potential sensors on neutral?
I referenced my entire circuit to neutral and had no differential
signals.

That might get interesting if the meters get used on 3-phase supplies.

John
Click to expand...

That's a more expensive meter. Circuit common can be earth ground. But
the CT outputs are isolated, so can be grounded, so there's still no
reason to fight a big common-mode signal.

I also designed a multi-channel meter, the C180, for end-use load
studies, that would meter any combination of phases and loads;
Blondel's Theorem applies. Its electronics were grounded. We sold
thousands of those, during the end-use-load-study fad. That's a nother
story.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a Êcrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin@highlandsniptechnology.com a Êcrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)
Click to expand...

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

George H.
*please ignore if you don't like silly ideas.
And habib, forgive the silly thread bend.
--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Click to expand...
 
On Tue, 28 Apr 2020 12:56:11 -0700 (PDT), George Herold
<ggherold@gmail.com> wrote:

On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 ŕ 21:31, John Larkin a écrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 ŕ 18:30, jlarkin@highlandsniptechnology.com a écrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

George H.
*please ignore if you don't like silly ideas.
And habib, forgive the silly thread bend.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Click to expand...

We had a voltage signal, from a resistive divider, and current signals
from current transformers, or a current shunt for the single-phase
India meter.

An ADC simultaneously samples voltage and current waveform pairs and
the uP does the math. Software autozero, multiply, average for power,
integrate for energy.

The sample rate need not be high; The Sampling Theorem does not apply.
The survey meters sampled each channel pair around 27 Hz. We added
some dither to the analog current signals to avoid ADC quantization
and differential linearity errors. It was kinda fun at the time, but
60 Hz is not my favorite speed range and sine waves are boring.

We still sell a few of these:

http://www.highlandtechnology.com/DSS/V180DS.shtml

mostly for aircraft 400 Hz testing, like APUs.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Tuesday, April 28, 2020 at 4:59:14 PM UTC-4, John Larkin wrote:
On Tue, 28 Apr 2020 12:56:11 -0700 (PDT), George Herold
ggherold@gmail.com> wrote:

On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a Êcrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin@highlandsniptechnology.com a Êcrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

George H.
*please ignore if you don't like silly ideas.
And habib, forgive the silly thread bend.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

We had a voltage signal, from a resistive divider, and current signals
from current transformers, or a current shunt for the single-phase
India meter.

An ADC simultaneously samples voltage and current waveform pairs and
the uP does the math. Software autozero, multiply, average for power,
integrate for energy.

The sample rate need not be high; The Sampling Theorem does not apply.
The survey meters sampled each channel pair around 27 Hz. We added
some dither to the analog current signals to avoid ADC quantization
and differential linearity errors. It was kinda fun at the time, but
60 Hz is not my favorite speed range and sine waves are boring.
Nice thanks. Some noise can be good I guess.
Click to expand...

But sure resistor divider and current transformer was my input
picture.. but then an opamp summing it into a resistor/ heater..
No! that can't work. I need the product...
Can I program some fet as heater?
(I was having this picture of a thermal oscillator, where
the period was related to the power... or inversely related.
long period = low power.)


We still sell a few of these:

http://www.highlandtechnology.com/DSS/V180DS.shtml

mostly for aircraft 400 Hz testing, like APUs.

Selling stuff is good.
Click to expand...

George H.
--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Click to expand...
 
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a Êcrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin@highlandsniptechnology.com a Êcrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?
Click to expand...

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.

Today's meter's do the same thing by measuring the instantaneous voltage and current and finding the product. It is easy to find various circuits to multiply two quantities. It's not hard to find various ways to measure voltage and current. Async voltage to PWM converters for both the voltage and the current taps, then use an XOR to find the instantaneous product. Smooth the pulses and you have an analog signal proportional to the instantaneous power.

Generate analog signals for the instantaneous voltage and current. Generate the log of the signals and sum them giving power. This would require the two inputs to be biased since the input to the log can't go through zero. The bias would be subtracted out at the end potentially creating a problem of a small difference of two large signals.

How about using the voltage to control a pump with the output pressure proportional to the voltage. The opening of a valve can be made proportional to the current and the volume of water would be the product measured by standard means. Or a gas could be used using the same measuring devices as a gas meter.

An excavator could be used to move boulders at a rate proportional to the voltage and a size proportional to the current. The brake is held on proportional to the phase lag. The fuel consumed is proportional to the energy.

An LED shines on a photocell with an LCD between them. The current to the LED is proportional to the instantaneous current in the wire. The number of pixels activated in the LCD is proportional to the instantaneous voltage to the meter and the illumination to the photocell is the product. Actually, that might not be totally ridiculous. The LCD would need to be worked some way so it doesn't need an entire digital controller. Is there some sort of shutter that could be proportional to a voltage? Or can the photocell response be modulated by a voltage?

Probably would have a limited range of accuracy. Like most measuring devices.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
 
On Tuesday, April 28, 2020 at 7:20:28 PM UTC-4, Ricky C wrote:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a Êcrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin@highlandsniptechnology.com a Êcrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free..fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.

Today's meter's do the same thing by measuring the instantaneous voltage and current and finding the product. It is easy to find various circuits to multiply two quantities. It's not hard to find various ways to measure voltage and current. Async voltage to PWM converters for both the voltage and the current taps, then use an XOR to find the instantaneous product. Smooth the pulses and you have an analog signal proportional to the instantaneous power.

Generate analog signals for the instantaneous voltage and current. Generate the log of the signals and sum them giving power. This would require the two inputs to be biased since the input to the log can't go through zero.. The bias would be subtracted out at the end potentially creating a problem of a small difference of two large signals.
Click to expand...

Thanks, except for PWM (and averaging) multiplying signals is
expensive or finicky.
I hadn't thought about adding logs, thanks again.

The heat from a fet, where you servo the voltage and current
has to equal the power... the trick would be measuring it.

George H.


How about using the voltage to control a pump with the output pressure proportional to the voltage. The opening of a valve can be made proportional to the current and the volume of water would be the product measured by standard means. Or a gas could be used using the same measuring devices as a gas meter.

An excavator could be used to move boulders at a rate proportional to the voltage and a size proportional to the current. The brake is held on proportional to the phase lag. The fuel consumed is proportional to the energy..

An LED shines on a photocell with an LCD between them. The current to the LED is proportional to the instantaneous current in the wire. The number of pixels activated in the LCD is proportional to the instantaneous voltage to the meter and the illumination to the photocell is the product. Actually, that might not be totally ridiculous. The LCD would need to be worked some way so it doesn't need an entire digital controller. Is there some sort of shutter that could be proportional to a voltage? Or can the photocell response be modulated by a voltage?

Probably would have a limited range of accuracy. Like most measuring devices.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
Click to expand...
 
On Tue, 28 Apr 2020 15:10:42 -0700 (PDT), George Herold
<ggherold@gmail.com> wrote:

On Tuesday, April 28, 2020 at 4:59:14 PM UTC-4, John Larkin wrote:
On Tue, 28 Apr 2020 12:56:11 -0700 (PDT), George Herold
ggherold@gmail.com> wrote:

On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 ŕ 21:31, John Larkin a écrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 ŕ 18:30, jlarkin@highlandsniptechnology.com a écrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

George H.
*please ignore if you don't like silly ideas.
And habib, forgive the silly thread bend.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

We had a voltage signal, from a resistive divider, and current signals
from current transformers, or a current shunt for the single-phase
India meter.

An ADC simultaneously samples voltage and current waveform pairs and
the uP does the math. Software autozero, multiply, average for power,
integrate for energy.

The sample rate need not be high; The Sampling Theorem does not apply.
The survey meters sampled each channel pair around 27 Hz. We added
some dither to the analog current signals to avoid ADC quantization
and differential linearity errors. It was kinda fun at the time, but
60 Hz is not my favorite speed range and sine waves are boring.
Nice thanks. Some noise can be good I guess.

But sure resistor divider and current transformer was my input
picture.. but then an opamp summing it into a resistor/ heater..
No! that can't work. I need the product...
Can I program some fet as heater?
(I was having this picture of a thermal oscillator, where
the period was related to the power... or inversely related.
long period = low power.)



We still sell a few of these:

http://www.highlandtechnology.com/DSS/V180DS.shtml

mostly for aircraft 400 Hz testing, like APUs.

Selling stuff is good.
Click to expand...

Yes. It's a kind of psychological validation; somebody important wants
it. The money can be useful too.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a Êcrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin@highlandsniptechnology.com a Êcrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free..fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.
Click to expand...

https://youtu.be/xtModjpxfxM
 
onsdag den 29. april 2020 kl. 02.50.46 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a Êcrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin@highlandsniptechnology.com a Êcrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.
Click to expand...

looks to me like it is just one line and one neutral
 
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 ŕ 21:31, John Larkin a écrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 ŕ 18:30, jlarkin@highlandsniptechnology.com a écrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM
Click to expand...

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
On Tue, 28 Apr 2020 18:01:10 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

onsdag den 29. april 2020 kl. 02.50.46 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 ŕ 21:31, John Larkin a écrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 ŕ 18:30, jlarkin@highlandsniptechnology.com a écrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.


looks to me like it is just one line and one neutral
Click to expand...

Right. The usual US meter has one voltage coil and two current coils.
That internal element has those two current coils, but looks to be
connected in the housing to only meter one current.

That would be very rare in the USA, to meter a single 120-N service.
That's ancient.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
onsdag den 29. april 2020 kl. 04.06.55 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 18:01:10 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 29. april 2020 kl. 02.50.46 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a Êcrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin@highlandsniptechnology.com a Êcrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors....
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.


looks to me like it is just one line and one neutral

Right. The usual US meter has one voltage coil and two current coils.
That internal element has those two current coils, but looks to be
connected in the housing to only meter one current.

That would be very rare in the USA, to meter a single 120-N service.
That's ancient.
Click to expand...

maybe for something like stair lights ?
 
On Tuesday, April 28, 2020 at 10:16:55 PM UTC-4, Lasse Langwadt Christensen wrote:
onsdag den 29. april 2020 kl. 04.06.55 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 18:01:10 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 29. april 2020 kl. 02.50.46 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a Êcrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin@highlandsniptechnology.com a Êcrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise..
(You'd have to have some means of getting rid of all the errors....
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.


looks to me like it is just one line and one neutral

Right. The usual US meter has one voltage coil and two current coils.
That internal element has those two current coils, but looks to be
connected in the housing to only meter one current.

That would be very rare in the USA, to meter a single 120-N service.
That's ancient.


maybe for something like stair lights ?
Click to expand...

Not likely to need a separate meter for stair lights, but we do have a lot of outdoor lights on tall poles all supplied by the power company. Typically they are billed with a fixed fee, but I believe some locations meter the electricity and bill accordingly. That could easily be 120VAC rather than 240VAC.

I noticed the unit in the video had a crack in the glass, so likely removed from service while still working.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209
 
On Tuesday, April 28, 2020 at 10:06:55 PM UTC-4, jla...@highlandsniptechnology.com wrote:
On Tue, 28 Apr 2020 18:01:10 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 29. april 2020 kl. 02.50.46 UTC+2 skrev jla...@highlandsniptechnology.com:
On Tue, 28 Apr 2020 17:15:36 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

onsdag den 29. april 2020 kl. 01.20.28 UTC+2 skrev Ricky C:
On Tuesday, April 28, 2020 at 3:56:23 PM UTC-4, George Herold wrote:
On Monday, April 27, 2020 at 5:10:31 PM UTC-4, John Larkin wrote:
On Mon, 27 Apr 2020 22:08:26 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 21:31, John Larkin a Êcrit :
On Mon, 27 Apr 2020 20:00:23 +0200, habib <h.bouazizviallet@free.fr
wrote:

Le 27/04/2020 à 18:30, jlarkin@highlandsniptechnology.com a Êcrit :
On Mon, 27 Apr 2020 15:13:53 +0200, habib <h.bouazizviallet@free.fr
wrote:

Hi,

I'm designing a precise Mains Energy Meter (Class 0.2). There's a
mandatory requirement in the design spec

* .. shall detect the homopolar (Phase-Neutral) current in range (10mA
... 30mA) with 10% accuracy

In this Spice implementation I expected CMRR of the circuit should be
60dB or so ... When i compare V_Common_mode and Vout with FFT, the 5KHz
is far that attenuation although the 50Hz Carrier is canceled.

Don't understand, the AD8605 has a comfortable open-loop gain/bandwith,
Please someone could explain me.

Version 4
SHEET 1 1956 680
WIRE -608 -288 -688 -288
WIRE -432 -288 -608 -288
WIRE -320 -288 -432 -288
WIRE -240 -288 -320 -288
WIRE -96 -288 -160 -288
WIRE 48 -288 -96 -288
WIRE 176 -288 48 -288
WIRE 304 -288 256 -288
WIRE -432 -240 -432 -288
WIRE -96 -240 -96 -288
WIRE -608 -160 -608 -288
WIRE 192 -160 192 -176
WIRE -688 -144 -688 -288
WIRE 48 -144 48 -288
WIRE 160 -144 48 -144
WIRE -432 -128 -432 -160
WIRE -432 -128 -544 -128
WIRE 304 -128 304 -288
WIRE 304 -128 224 -128
WIRE 352 -128 304 -128
WIRE -96 -112 -96 -160
WIRE -16 -112 -96 -112
WIRE 160 -112 48 -112
WIRE -432 -96 -432 -128
WIRE -96 -80 -96 -112
WIRE 192 -80 192 -96
WIRE -16 32 -16 -112
WIRE 176 32 -16 32
WIRE 224 32 224 0
WIRE -688 48 -688 -64
WIRE -608 48 -608 -80
WIRE -608 48 -688 48
WIRE -432 48 -432 -16
WIRE -432 48 -608 48
WIRE -320 48 -432 48
WIRE -256 48 -320 48
WIRE -96 48 -96 0
WIRE -96 48 -176 48
WIRE 48 48 48 -112
WIRE 48 48 -96 48
WIRE 448 64 448 -16
WIRE -544 80 -544 -128
WIRE 112 112 112 96
WIRE 176 128 176 32
WIRE 176 128 144 128
WIRE -16 144 -16 32
WIRE 80 144 -16 144
WIRE 224 160 224 112
WIRE 224 160 144 160
WIRE 112 192 112 176
WIRE 448 192 448 144
WIRE 224 208 224 160
WIRE 224 320 224 288
WIRE -544 336 -544 160
FLAG 192 -80 0
FLAG 352 -128 out
FLAG 448 -16 p3v3
FLAG 224 0 p3v3
FLAG 192 -176 p3v3
FLAG 448 192 0
FLAG -16 -112 mid
FLAG -320 -288 Hi
FLAG -320 48 Lo
FLAG -544 336 0
FLAG 112 192 0
FLAG 112 96 p3v3
FLAG 224 320 0
FLAG -432 -128 V_Common_Mode
SYMBOL res 272 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 330K
SYMBOL res -80 16 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res -80 -144 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res 208 128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 208 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL res -624 -176 R0
SYMATTR InstName R6
SYMATTR Value {Rburden}
SYMBOL current -688 -64 R180
WINDOW 0 24 80 Left 2
WINDOW 3 24 0 Left 2
WINDOW 123 24 52 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value SINE(0 10u 50)
SYMBOL voltage 448 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 3.3
SYMBOL Opamps\\AD8505 192 -192 R0
SYMATTR InstName U1
SYMBOL res -144 -304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 806
SYMBOL res -160 32 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 806
SYMBOL res -448 -256 R0
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -448 -112 R0
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL voltage -544 64 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR InstName V_Common_Mode
SYMATTR Value SFFM(0 1 50 0.8 5000)
SYMBOL Opamps\\AD8505 112 80 M0
SYMATTR InstName U2
TEXT 360 -248 Left 2 !.tran 100m
TEXT -928 -24 Left 2 !;.step param I_mes 10u 100u 10u
TEXT -448 288 Left 2 !;ac dec 200 10 1meg
TEXT -1016 -176 Left 2 ;I1 represent a CT 1:2000 ratio
TEXT -1240 -208 Left 2 ;I1 Homopolar Current betwenn Ph and Neutral wires
TEXT -992 72 Left 2 !.step param Rburden 10 50 10


The burdened CT output is already a nice low-impedance voltage source.
By floating it and grounding through the 10K resistors, you are
begging capacitively-coupled currents to make big common-mode
voltages, which then require a super diffamp to reject.
The resistors accuracy (0.1%), the temp drifts along with the overall
gain are the main parameters for increase CMRR. AFAIK.

Having no common-mode signal to reject is even better.


I'd consider using the CT output single-ended, or at least split the
burden and ground the center tap.
John,
It should need a symmetrical power supplies (p3v3 and n3v3) for the op
amp and overall system, which I'm not allowed to do.

Then DC shift the CT up, and bypass it to ground.


Not sure that symmetrical power supplies could resolve common mode
phenomenon. It is really hard to master it in Mains Voltage /Currents
measurements.

AC grounding one end of the CT, or AC grounding the center tap of the
burden resistor, kills the common-mode signal. Your model assumes a
small common-mode voltage. Your signal is small, and the common-mode
noise, with the 10K resistors, could be huge.
AC grounding should be a nice solution. Beside this you're right the
homopolar current (the fault current to ground) is (very) small in my
design so I should select a CT with less ratio; 1:100 ratio should help.
Thanks.


I'd suggest some high-frequency rolloff too. Power lines can be nasty.

You might look up the circuits of existing ground-fault detectors.
There are dirt-cheap chips available for that, and their data sheets
and appnotes could be useful.




I designed and built some prototypes of an electric meter, for Niagra
Mohawk, intended for use in India. The project didn't go, but the
meter worked. It had inductive power and data transfer, so it could be
read out even when the line power was down. We did something similar
to GFD, but it was to catch people stealing power, more than for
safety. Seems that people in India steal power almost as often as
people in New York City.

In NYC, I've heard stories of company X drilling through a wall to
steal from Y, and simultaneously vice versa.

Designing an electronic meter that's as good as the old rotating disks
is surprisingly difficult. See ANSI C12.

Hmm, Re: old rotating disk things (and silly ideas*)

I know almost nothing about power measurement.
I first wonder if you need a fast output. The disk
meters have a built in averaging function.
And so I'm sitting here thinking about ways to measure
average power over some time. (total energy.)
My first silly idea is to send a 'surrogate' of the voltage
and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors....
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.


https://youtu.be/xtModjpxfxM

That meter uses one voltage coil line-line, and two current coils.
That assumes that the 120-0-120 volt line is symmetric, which is
imperfect but saves money in the meter.


looks to me like it is just one line and one neutral

Right. The usual US meter has one voltage coil and two current coils.
That internal element has those two current coils, but looks to be
connected in the housing to only meter one current.

That would be very rare in the USA, to meter a single 120-N service.
That's ancient.
Click to expand...

The last meter I saw for 120V was installed in 1945, and removed in 1966 from the garage of a house my parents bought when I was starting high school. The original owner had built a small cottage to live in while the actual house was built. After that, they cut away most of the wood floors to use it for a garage. My dad and I finished removing a center wall, and the rest of the floor because '60s cars were too wide for the missing wood. We had the separate 120V service turned off, then I ran 240 to it from the main house. My first Electronics workshop was built on the back of that building while I was in high school.
 
On Wednesday, April 29, 2020 at 12:46:36 AM UTC-4, upsid...@downunder.com wrote:
On Tue, 28 Apr 2020 16:20:22 -0700 (PDT), Ricky C
gnuarm.deletethisbit@gmail.com> wrote:

But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.

Today's meter's do the same thing by measuring the instantaneous voltage and current and finding the product. It is easy to find various circuits to multiply two quantities. It's not hard to find various ways to measure voltage and current. Async voltage to PWM converters for both the voltage and the current taps, then use an XOR to find the instantaneous product. Smooth the pulses and you have an analog signal proportional to the instantaneous power.

Generate analog signals for the instantaneous voltage and current.
Generate the log of the signals and sum them giving power.

log(U) + log(I) = log(P)

If you need to sum (for averaging) individual power samples, you need
to use antilog( log(P) ) before summing different samples. The
exponential function required dynamic range is much larger than for
either log(U) or log(I).

This would require the two inputs to be biased since the input to the log can't go through zero. The bias would be subtracted out at the end potentially creating a problem of a small difference of two large signals.

Just use abs() (full wave rectification) before the log(),
Click to expand...

There will be times of zero current and/or voltage. It's not about the sign. It's about the undefined nature of log(0) and what happens as you approach it. I can't think of a way to deal with this issue other than to add a bias. I suppose the two could be combined, abs() with a small bias added making the difference between large numbers only an issue at low values. But this is not a very practical solution anyway.

A bit of making a silk purse from a sow's ear... or gilding the lily. Pick one.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209
 
On Tue, 28 Apr 2020 16:20:22 -0700 (PDT), Ricky C
<gnuarm.deletethisbit@gmail.com> wrote:

But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.

Today's meter's do the same thing by measuring the instantaneous voltage and current and finding the product. It is easy to find various circuits to multiply two quantities. It's not hard to find various ways to measure voltage and current. Async voltage to PWM converters for both the voltage and the current taps, then use an XOR to find the instantaneous product. Smooth the pulses and you have an analog signal proportional to the instantaneous power.

Generate analog signals for the instantaneous voltage and current.
Generate the log of the signals and sum them giving power.
Click to expand...

log(U) + log(I) = log(P)

If you need to sum (for averaging) individual power samples, you need
to use antilog( log(P) ) before summing different samples. The
exponential function required dynamic range is much larger than for
either log(U) or log(I).

>This would require the two inputs to be biased since the input to the log can't go through zero. The bias would be subtracted out at the end potentially creating a problem of a small difference of two large signals.

Just use abs() (full wave rectification) before the log(),
 
On 2020-04-28, Ricky C <gnuarm.deletethisbit@gmail.com> wrote:

and current through a resistor and measure the temperature rise.
(You'd have to have some means of getting rid of all the errors...
Like some sort of differential gizmo that heats and cools
(to environment) and known I*V as a calibration.. the details
are a bit fuzzy. :^)
But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one
Click to expand...
for voltage. Their effect on an aluminum disk is proportional to the
product including the phase angle, in other words the complex product
of voltage and current. The meter has fixed magnets that create drag
making the rotational speed of the rotor proportional to the power
being drawn.
So really the meter is measuring the voltage and the current
Click to expand...
including the relative phase, then finding the product though the EM
effects on the disk.


Today's meter's do the same thing by measuring the instantaneous
voltage and current and finding the product. It is easy to find
various circuits to multiply two quantities. It's not hard to find
various ways to measure voltage and current. Async voltage to PWM
converters for both the voltage and the current taps, then use an XOR
to find the instantaneous product. Smooth the pulses and you have an
analog signal proportional to the instantaneous power.
Click to expand...

seems kind of dodgy, you need to keep those two clocks decorellated.

Generate analog signals for the instantaneous voltage and current.
Generate the log of the signals and sum them giving power. This would
require the two inputs to be biased since the input to the log can't
go through zero. The bias would be subtracted out at the end
potentially creating a problem of a small difference of two large
signals.
Click to expand...

bias precision could be a problem, you have the same issue with the
PWM scheme.

pass a current proportional to line voltage through a hall effect cell and
derive the magnetic field from the line current

output voltage will be proportional to istantaneous power.
--
Jasen.
 
On Wed, 29 Apr 2020 07:46:30 +0300, upsidedown@downunder.com wrote:

On Tue, 28 Apr 2020 16:20:22 -0700 (PDT), Ricky C
gnuarm.deletethisbit@gmail.com> wrote:

But I was wondering if there are other 'silly' ways
to measure power/ energy*time?

The old disk meters actually use two coils, one for current and one for voltage. Their effect on an aluminum disk is proportional to the product including the phase angle, in other words the complex product of voltage and current. The meter has fixed magnets that create drag making the rotational speed of the rotor proportional to the power being drawn.

So really the meter is measuring the voltage and the current including the relative phase, then finding the product though the EM effects on the disk.

Today's meter's do the same thing by measuring the instantaneous voltage and current and finding the product. It is easy to find various circuits to multiply two quantities. It's not hard to find various ways to measure voltage and current. Async voltage to PWM converters for both the voltage and the current taps, then use an XOR to find the instantaneous product. Smooth the pulses and you have an analog signal proportional to the instantaneous power.

Generate analog signals for the instantaneous voltage and current.
Generate the log of the signals and sum them giving power.

log(U) + log(I) = log(P)

If you need to sum (for averaging) individual power samples, you need
to use antilog( log(P) ) before summing different samples. The
exponential function required dynamic range is much larger than for
either log(U) or log(I).

This would require the two inputs to be biased since the input to the log can't go through zero. The bias would be subtracted out at the end potentially creating a problem of a small difference of two large signals.

Just use abs() (full wave rectification) before the log(),
Click to expand...

The instantaneous power product goes negative when the power factor is
<1. You've got to preserve the signs.

Just multiply! Preferably in software.

A utility-class meter might handle 30KW and needs to be accurate to a
few watts. That's borderline impossible to do with analog electronics,
borderline trivial with a mediocre ADC and a cheap uP.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
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