AC and meter movements

[Phil Allison]

"Alfred E. Schoen"

** Moving iron meters always read "true RMS" - within the limits of
their frequency responses.

The force on the pointer is proportional to the average of the *square*
of the applied current ( hence it automatically rectifies AC) - and the
scale on the face is somewhat non linear as it indicates actual current.

I have used and calibrated iron vane meters, and I don't remember them as
true RMS for all waveforms.

** That is why I added the qualification: " within ..... "

Missed that, did you ????

Particularly, they have a slightly different response to a DC component,

** Really?

Would not that be because the readings tends to fall as the frequency rises
??

Here is some information about older RMS metering devices:
http://ca.fluke.com/Fluke/usen/Community/Fluke+Plus/ArticleCategories/DMMs/True-rms+Facts.htm

** Bollocks.

The article only mentions them in passing - you pathetic bullshit artist.

( snip more irrelevant shite)

I found other references that state true-RMS performance of iron-vane
instruments, and perhaps they do respond accurately, although they are
definitely limited in frequency response to power-line and low audio
signals.

** That is why I added the qualification: " within ..... "

Missed that, did you ????

Without actually performing tests I will accept that iron vane types are
at least better than rectifier types for RMS readings. Here is a
discussion with much detail that seems to prove your assertion:
http://yarchive.net/electr/analog_voltmeters.html

** How fucking patronising.

AC current is best measured with a CT, and there are some small
inexpensive ones that will handle currents of 5 to 30 amps with a ratio of
about 500:1 such as this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=237-1103-ND

The output can be rectified and provides a current of 10 mA for 5 A with
enough voltage to produce a linear output through a silicon diode bridge.

** Absolute BOLLOCKS!!

That CT is speced to use a 60 ohm load resistor and it outputs 1.65V at 15
amps - however a silicon diode bridge will not even *begin conducting*
until the AC voltage reaches 0.7V rms.

Means the meter scale will be HORRIBLY non-linear and will be MISSING the
lower half of the range ENTIRELY !!!!

OTOH - by simply using a suitable Moving Iron meter, no current tranny is
needed and it will read the true rms value including any DC component in the
load current.

Piss off - wanker.



..... Phil

 

On Sun, 11 Apr 2010 10:52:33 -0700, Fred Abse
<excretatauris@invalid.invalid> wrote:

On Sun, 11 Apr 2010 05:05:01 -0500, phantom wrote:

On Sun, 11 Apr 2010 12:32:23 +1000, "Phil Allison" <phil_a@tpg.com.au
wrote:


"The Phantom"


You can also get moving iron voltmeters which will read true RMS.

** Moving iron meters always read "true RMS" - within the limits of their
frequency responses.

Why are you repeating what I already told the OP? I already explained
to him that moving iron voltmeters read true RMS.

No, you said "You can also get moving iron voltmeters which will read true

So I did, and it is quite true. In addition to moving iron ammeters,
you can ALSO get moving iron voltmeters, and they do indeed read true
RMS. I never said anything to the effect that only some moving iron
voltmeters read true RMS.

I first described moving iron ammeters which read true RMS, explained
about scale problems to watch out for, and then I told him that (as
well as ammeters), you can ALSO get moving iron voltmeters (the)
which read true RMS.

If you and Phil think that I was saying that only some moving iron
voltmeters read true RMS, that is your mistake, not mine.

RMS."

"also"



The force on the pointer is proportional to the average of the *square*
of the applied current ( hence it automatically rectifies AC) - and
the scale on the face is somewhat non linear as it indicates actual
current.


Phil is correct.

 

On Sun, 11 Apr 2010 22:18:47 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

phantom@aol.com


You can also get moving iron voltmeters which will read true RMS.


** Moving iron meters always read "true RMS" - within the limits of their
frequency responses.

Why are you repeating what I already told the OP? I already explained
to him that moving iron voltmeters read true RMS.


** Fraid you told the world that only * SOME* of them did.

The word "some" is not in what I said, only in your brain.

Read your own words - dickhead.

I don't need to read them; I wrote them.

You're the one who is always criticizing others for not paying
attention to the context.

I was first descirbing moving iron ammeters, which read true RMS, then
I told the OP that "You can also get moving iron voltmeters which will
(also) read true RMS (just as moving iron ammeters do). The entire
context is about moving iron meters and the parentheticals are implied
by the context. If you didn't understand it, you're not paying
attention to the context.

.... Phil

 

[Phil Allison]

<phantom@aol.com>

I first described moving iron ammeters which read true RMS,

** You never said a thing about MI ammeters being " true RMS " and the
matter was not raised before.

The wording YOU used was misleading and wrong !!

That you now try to re-word the whole thing proves the point.

My post stated the case clearly and gave an explanation too.


Your whining about it is PATHETIC !!



..... Phil

 

[Phil Allison]

<phantom@aol.com>

** Moving iron meters always read "true RMS" - within the limits of
their
frequency responses.

Why are you repeating what I already told the OP? I already explained
to him that moving iron voltmeters read true RMS.


** Fraid you told the world that only * SOME* of them did.

The word "some" is not in what I said,

** Fraid it is strongly implied by your choice of words.

Read your own words - dickhead.

I don't need to read them;

** Fraid you do - cos you are so fucking illiterate.

I was first descirbing moving iron ammeters, which read true RMS,

** Fraid you did NOT mention that fact at all.

Your ridiculous whining is PATHETIC.

Piss OFF !!!



...... Phil

 

On Sun, 11 Apr 2010 22:18:47 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

phantom@aol.com


You can also get moving iron voltmeters which will read true RMS.


** Moving iron meters always read "true RMS" - within the limits of their
frequency responses.

Why are you repeating what I already told the OP? I already explained
to him that moving iron voltmeters read true RMS.


** Fraid you told the world that only * SOME* of them did.

I said "You can also get moving iron voltmeters which will read true

RMS."

I could have said "You can also get moving iron voltmeters (some of)
which will read true RMS."

Or, I could have said "You can also get moving iron voltmeters (a few
of) which will read true RMS."

Or, I could have said "You can also get moving iron voltmeters (most
of) which will read true RMS."

Or, I could have said "You can also get moving iron voltmeters (all
of) which will read true RMS."

I didn't bother to use the last locution because the convention in
English is to take a missing quantifier to be the universal quantifier
"all". If you want to take it to be something else, you certainly
may, but don't attribute an error to me because of your choice.

 

[Phil Allison]

<phantom@aol.com>

** Fraid you told the world that only * SOME* of them did.

The word "some" is not in what I said,

** Fraid it is strongly implied by your choice of words.

Read your own words - dickhead.

I don't need to read them;

** Fraid you do - cos you are so fucking illiterate.

I was first descirbing moving iron ammeters, which read true RMS,

** Fraid you did NOT mention that fact at all.

Your ridiculous whining is PATHETIC.

Piss OFF !!!



...... Phil

 

[Paul E. Schoen]

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:82fb2bFj53U1@mid.individual.net...

"Alfred E. Schoen"

** Moving iron meters always read "true RMS" - within the limits of
their frequency responses.

The force on the pointer is proportional to the average of the *square*
of the applied current ( hence it automatically rectifies AC) - and
the scale on the face is somewhat non linear as it indicates actual
current.

I have used and calibrated iron vane meters, and I don't remember them as
true RMS for all waveforms.

** That is why I added the qualification: " within ..... "

Missed that, did you ????

No, just restating what you said in different words.

Particularly, they have a slightly different response to a DC component,

** Really?

Would not that be because the readings tends to fall as the frequency
rises ??

Actually, from what I read, it is because of remanent magnetism at power
line frequencies. But also the frequency effect which probably kicks in at a
few kHz.

Here is some information about older RMS metering devices:
http://ca.fluke.com/Fluke/usen/Community/Fluke+Plus/ArticleCategories/DMMs/True-rms+Facts.htm

** Bollocks.

The article only mentions them in passing - you pathetic bullshit
artist.

( snip more irrelevant shite)


I found other references that state true-RMS performance of iron-vane
instruments, and perhaps they do respond accurately, although they are
definitely limited in frequency response to power-line and low audio
signals.

** That is why I added the qualification: " within ..... "

Missed that, did you ????

No, just restating what you said in different words.

Without actually performing tests I will accept that iron vane types are
at least better than rectifier types for RMS readings. Here is a
discussion with much detail that seems to prove your assertion:
http://yarchive.net/electr/analog_voltmeters.html

** How fucking patronising.

Take offense if you feel the need. I was only providing additional
information and agreeing with you.

AC current is best measured with a CT, and there are some small
inexpensive ones that will handle currents of 5 to 30 amps with a ratio
of about 500:1 such as this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=237-1103-ND

The output can be rectified and provides a current of 10 mA for 5 A with
enough voltage to produce a linear output through a silicon diode bridge.

** Absolute BOLLOCKS!!

That CT is speced to use a 60 ohm load resistor and it outputs 1.65V at 15
amps - however a silicon diode bridge will not even *begin conducting*
until the AC voltage reaches 0.7V rms.

The resistor needs to be placed after the rectifier.

Means the meter scale will be HORRIBLY non-linear and will be MISSING the
lower half of the range ENTIRELY !!!!

OTOH - by simply using a suitable Moving Iron meter, no current tranny
is needed and it will read the true rms value including any DC component
in the load current.

You are correct in saying that the output is non-linear, but it can supply
usable readings from about 2 amps to well over 30 amps. We use this exact
part in a design and here are some actual data:

Amps VDC(24ohms) V/A
1 0.004 0.004
2 0.041 0.020
4 0.119 0.030
5 0.163 0.033
6 0.202 0.034
7 0.238 0.034
8 0.281 0.035
9 0.319 0.035
10 0.362 0.036
12 0.442 0.037
15 0.554 0.037
20 0.743 0.037
25 0.904 0.036
30 1.031 0.034
35 1.147 0.033
40 1.248 0.031
45 1.328 0.029
50 1.408 0.028
55 1.538 0.028
60 1.638 0.027
65 1.738 0.027

This is linear enough to be used for metering and it allows the use of a DC
meter or a simple A/D converter in a PIC, as is used in our device. In this
case, we can use a conversion table to linearize the results, but it would
also work with a custom drawn scale on an analog meter. It is probably more
linear than most iron vane meters, which are also not very responsive at the
low end. Actually, the nonlinearity provides an expanded scale in the middle
of the range, which gives greater readability, and the end of the scale is
compressed which allows readings of higher currents.

Germanium or Schottkey diodes would perform much better, of course. And
there is also the problem of variations due to temperature. So a precision
rectifier or direct AC measurement (without the bridge rectifier) are much
better, but add complexity.

Paul

 

[Mike Cook]

For the OP's purposes of voltage measurement, a silicon or germanium diode
bridge will work well, and can be used with most commonly available meters.
AC current is best measured with a CT, and there are some small inexpensive
ones that will handle currents of 5 to 30 amps with a ratio of about 500:1
such as this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=237-1103-ND

The output can be rectified and provides a current of 10 mA for 5 A with
enough voltage to produce a linear output through a silicon diode bridge.

Paul

Excellent. Thank you Paul for the CT explanation. That looks like my solution
for ampere measurement.

Cheers.

 

[Phil Allison]

"Alfred E. Schoen"

AC current is best measured with a CT, and there are some small
inexpensive ones that will handle currents of 5 to 30 amps with a ratio
of about 500:1 such as this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=237-1103-ND

The output can be rectified and provides a current of 10 mA for 5 A with
enough voltage to produce a linear output through a silicon diode
bridge.

** Absolute BOLLOCKS!!

That CT is speced to use a 60 ohm load resistor and it outputs 1.65V at
15 amps - however a silicon diode bridge will not even *begin
conducting* until the AC voltage reaches 0.7V rms.

The resistor needs to be placed after the rectifier.

** Shame you did not say that before.

The behaviour of the CT with such a load is not defined.

Big shame that any DC component is not read as it would be with a simple MI
meter.

The CT would be screwed completely by a significant DC component.

Germanium or Schottkey diodes would perform much better, of course.

** Of course.

Beam me up - Schottky !!!!!!!!!!!

And there is also the problem of variations due to temperature.

** Blah, blah, blah ...



..... Phil

 

[Paul E. Schoen]

"Mike Cook" <mcham@NOTyahoo.com> wrote in message
news:0001HW.C7E813D6005CAE3CB01AD9AF@news.eternal-september.org...

For the OP's purposes of voltage measurement, a silicon or germanium
diode
bridge will work well, and can be used with most commonly available
meters.
AC current is best measured with a CT, and there are some small
inexpensive
ones that will handle currents of 5 to 30 amps with a ratio of about
500:1
such as this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=237-1103-ND

The output can be rectified and provides a current of 10 mA for 5 A with
enough voltage to produce a linear output through a silicon diode bridge.

Paul

Excellent. Thank you Paul for the CT explanation. That looks like my
solution
for ampere measurement.

Cheers.

Please read my reply to Phil for more information. This CT circuit with
silicon diodes is not very linear and it may not even show any current below
about 1 ampere. It should be much better if you use germanium diodes or
Schottkys. You may also consider using something like an old small audio
output transformer with a 4 ohm secondary used for current, and the primary
may have enough turns to drive a bridge rectifier.

Best of luck,

Paul

 

[Paul E. Schoen]

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:hpukke$4u6$1@news-01.bur.connect.com.au...

"Alfred E. Schoen"

AC current is best measured with a CT, and there are some small
inexpensive ones that will handle currents of 5 to 30 amps with a ratio
of about 500:1 such as this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=237-1103-ND

The output can be rectified and provides a current of 10 mA for 5 A
with enough voltage to produce a linear output through a silicon diode
bridge.

** Absolute BOLLOCKS!!

That CT is speced to use a 60 ohm load resistor and it outputs 1.65V at
15 amps - however a silicon diode bridge will not even *begin
conducting* until the AC voltage reaches 0.7V rms.

The resistor needs to be placed after the rectifier.


** Shame you did not say that before.

The behaviour of the CT with such a load is not defined.

That is the standard connection for rectifier type AC current meters, and I
did not think it needed to be stated. But this is a basics newsgroup and I
should have been more specific. When I worked as a meter technician I
assembled and calibrated many meters which contained a small CT and copper
oxide rectifier directly to the meter movement, or with a small resistor to
provide adjustment and damping.

A CT with a bridge rectifier on its output very quickly generates enough
voltage to overcome the forward drop of two diodes. For a 500:1 ratio CT,
the primary voltage only needs to be about 3 mV. It also depends on the VA
rating of the CT (in this case about 2 VA), and the coupling of the primary
winding to the core and the core to the secondary, and the magnetic
characteristics of the core. These are complex and not well defined, as you
stated.

Big shame that any DC component is not read as it would be with a simple
MI meter.

The CT would be screwed completely by a significant DC component.

Yes, but the OP wanted to read AC current from a variable transformer and
most likely without any DC component. A search for an iron vane AC amps
panel meter turned up this one, from Simpson, distributed by Grainger, for
about $90:
http://www.grainger.com/Grainger/items/1T865?Pid=search

Iron vane meters tend to be fairly rare and expensive, as well as being
bulky and possibly not as rugged as most DC meters with a D'Arsonval
movement. Here are some cheap AC panel meters. They might be iron vane or
rectifier type:
http://www.mpja.com/prodinfo.asp?number=17683+ME
http://www.mpja.com/prodinfo.asp?number=8735+ME
http://www.mpja.com/prodinfo.asp?number=17255+ME
http://www.mpja.com/prodinfo.asp?number=16558+ME

The following information about Yogogawa meters states that iron-vane
*voltmeters* may exhibit inaccuracy of as much as 75% at the extremes of
rated frequency from 20 to 400 Hz, so the frequency effect is quite
significant. But for iron vane *ammeters*, the frequency effect is very
small:
http://www.yokogawa.com/us/mi/pdf/Panel_Meters_250260PM_01E_A_Apr2007.pdf

The specs for Triplett iron vane meters indicate an effect of 1% over the
range of 25-133 Hz.
http://www.electro-meters.com/Assets/PDF_files/Triplett/APM/Characteristicsr.pdf

Germanium or Schottkey diodes would perform much better, of course.

** Of course.

Beam me up - Schottky !!!!!!!!!!!

Spelling correction acknowledged. Proceed...

Paul

 

[Phil Allison]

"Alfred E. Schoen"

** He still hasn't got this one ....

The resistor needs to be placed after the rectifier.

** Shame you did not say that before.

The behaviour of the CT with such a load is not defined.

That is the standard connection for rectifier type AC current meters,

** Fraid that is something not seen everyday in electronics.

and I did not think it needed to be stated.

** Shows just what a total fuckwit you are.

But this is a basics newsgroup..

** It is a basic *electronics* NG !!

and I should have been more specific.

* You should never allude to things outside the realm of electronics as if
they are inside it.

When I worked as a meter technician

** Not an electronics job.

It is related to electrical engineering.

I assembled and calibrated many meters which contained a small CT and
copper oxide rectifier directly to the meter movement, or with a small
resistor to provide adjustment and damping.

** Bully for you.

Big shame that any DC component is not read as it would be with a simple
MI meter.

The CT would be screwed completely by a significant DC component.

Yes, but the OP wanted to read AC current from a variable transformer and
most likely without any DC component.

** Massive false assumption !!!!!!!!!

The load presented to a variac can be almost anything, including half wave
rectified which may be deliberate of the result of faulty equipment. A
faulty bridge in a SMPS, a faulty triac in a lamp dimmer etc.

A search for an iron vane AC amps panel meter turned up this one, from
Simpson, distributed by Grainger, for about $90:

** You can pick nice ones up on Ebay for low prices.

Links were supplied here days ago.

Piss off you damn fool.



...... Phil

 

[Phil Allison]

"Alfred E. Schoen"

You may also consider using something like an old small audio
output transformer with a 4 ohm secondary used for current,

** Totally INSANE - DO NOT ATTEMPT THIS !!!!!!!!!!!!

and the primary may have enough turns to drive a bridge rectifier.

** The 4 ohm winding of a small audio tranny will never handle 15 amps at
50Hz .

You FUCKING IDIOT !!!



..... Phil