Amplitude Time Ave. w/o Rectification

[glen herrmannsfeldt]

In comp.dsp Bret Cahill <BretCahill@peoplepc.com> wrote:
(snip, I wrote)

Instantaneous power is proportional to the square of the voltage
or current, not including resistance changes due to heating,
and so is always positive.  Is that rectification?  It seems
to me that any conversion of an AC signal with the DC component
removed to one that is always positive is a form of rectification,
but others might disagree.

Temperature may not be as convenient as radiation or voltage to
transmit information at high frequency but there is no reason not to
treat it as a signal.

There used to be a term 'detector', and 'detection' for extracting
the modulating signal from (at least an AM modulated) signal.

You can put the signal through almost any non-linear operation,
then low-pass filter the result, to extract in some form the
modulation. In the context of RF demodulation, I am not sure
of the exact meaning of 'rectification.' With some filtering
and such, you can extract either the half-wave or full-wave
rectified version of a modulated carrier from the input, which
would seem to qualify as rectification. If the non-linear
operation has even powers other than zero, that is pretty close
to rectification. If only odd powers, then maybe not.

-- glen

 

[glen herrmannsfeldt]

In comp.dsp Fred Marshall <fmarshall_xremove_the_xs@xacm.org> wrote:
(snip)

Multiplying by other than a constant or a stable periodic waveform is a
non-linear operation. Multiplying by a constant or a sinusoid or a sum
of sinusoids is a linear operation.... believe it or not.

Hmmm. As I understand it (longer ago than I remember) they used
to make rectifiers out of synchronous motor driven commutators.

That is, multiply by a square wave (sum of sines) of the appropriate
frequency. The result doesn't seem like a linear function of
the input anymore.

-- glen

 

[glen herrmannsfeldt]

In comp.dsp Bret Cahill <BretCahill@peoplepc.com> wrote:
(snip)

Poorly written OP. The goal is getting the amplitude _without_
rectification. Rectification" is to be very broadly construed and
includes anything that results in the final "signal" being positive at
all times.

Maybe peak to peak wil work if you know the wave form.

I still have my Heathkit VTVM, christmas present from when
I was in high school. The manual includes an explanation of
the form of rectifier used, and why the result is peak-to-peak.
Other than that, it seems unusual to rectify as peak-to-peak.

-- glen

 

[glen herrmannsfeldt]

In comp.dsp Fred Marshall <fmarshall_xremove_the_xs@xacm.org> wrote:
(snip on heater vs. rectifier)

The example of the heater is a good one. It does the job. One could
call it a nonlinear element because it's insensitive to the direction of
flow of current. But, I wouldn't call it a rectifier in the normal
sense. It's a transducer; converting current to heat. And, one does
lose the polarity/direction of the forcing function in the transduction.
So, it likely has to be modeled as a nonlinear element.

It might be that I am remembering vacuum gauges, but I believe
it is done by spot welding two wires together where they cross.
The result, then, is a combination of heater (two of the wires)
and thermocouple (the other two), at the point where they cross.

Power goes as voltage or current squared, heating the junction,
and the thermoelectric voltage, at least in small signal terms,
is proportional to the temperature change. It also has a built
in low-pass filter, due to the thermal mass.

Your stated objective, if I understand its definition, would likewise be
insensitive to the polarity of the signal wouldn't it?

Either that, or with certain assumptions, one might ignore all signal
components of the "wrong" polarity / direction - and that's pretty much
a half-wave rectifier.

-- glen

 

[glen herrmannsfeldt]

In comp.dsp Vladimir Vassilevsky <nospam@nowhere.com> wrote:

glen herrmannsfeldt wrote:

You can put the signal through almost any non-linear operation,

You can put the signal into the heater and measure the temperature.
Where is nonlinearity?

The temperature is a non-linear function of the voltage or current.
At best it is quadratic, which is pretty non-linear. I know
it doesn't go down when the current reverses.

You can put the signal into a into a solenoid and measure the force
attracting a piece of ferrous material. Or, for that matter, the force
between two solenoids with the same current running in them.

Both abs(x) and x**2 are non-linear.

There is a zillion of ways to measure AC without any
nonlinearity or rectification involved.

I am a little unsure of the exact meaning of rectification.

The google define:rectification includes "converting AC to DC."
That seems fine in the case of power supplies, but doesn't work
so well in the signal-processing sense. The output of either
a half or full wave rectifier, unfiltered, has a large AC component.
The important point being that the average (low pass filter)
output is non-zero.

So, it seems to me that in the appropriate sense, any operation
which converts the modulated carrier with no DC component to
one with a DC component, a process that can't happen with
linear operations, counts as rectification.

Now, some non-linear functions, though with odd powers, don't
result in a DC component in the result. In that case, it is harder
to call them rectifiers. If you add a DC offset to the input,
though, then you get rectification. (1+x)**3 has even powers.

On the other hand, I do agree that curve fitting to points
on the V(t) curve doesn't seem like rectification, and does allow
one to compute the amplitude, though not easily the envelope for
an AM modulated carrier.


-- glen

 

[Michael A. Terrell]

Vladimir Vassilevsky wrote:

Bret Cahill wrote:

Is there anyway to get an amplitude of an ac signal averaged over time
w/o some kind of rectification?

Sure. Connect the AC to a heater and measure the temperature.

This doesn't include the trivial, i.e., dc offsets or partial cycles.
The rectification could be analog, digital or software.

What are you really trying to do?

Troll the newsgroup, as always.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

 

[Mark]

On the other hand, I do agree that curve fitting to points
on the V(t) curve doesn't seem like rectification, and does allow
one to compute the amplitude, though not easily the envelope for
an AM modulated carrier.

-- glen

I think the key point is not about rectification or linear vs non
linear.

I think the key point is that the usual "rectification" methods
require some kind of explicit or implicit (in the case of a heaters)
low pass filtering to remove the carrier component and keep the
modulation component. The Hilbert method describe by R. Lyons
requires no filtering and returns an exact result regardless of the
relationship between the carrier frequency and the modulation.

That is the beauty of it.

That is the problem I saw many years ago, if you applied a lot of
filtering to the diode detector to completely remove the 455 kHz IF
signal, you would loose some of the high frequency audio components.
Of course I was using simple RC filters, I know better now of
course.

But, to me, that is the ___fundamental__ advantage of the Hilbert
method over the "rectifier" methods.

Hello Rick, I already have the received the errata from you. thank
you.


Mark

 

[glen herrmannsfeldt]

In comp.dsp Mark <makolber@yahoo.com> wrote:
(snip, I wrote)

On the other hand, I do agree that curve fitting to points
on the V(t) curve doesn't seem like rectification, and does allow
one to compute the amplitude, though not easily the envelope for
an AM modulated carrier.

I think the key point is not about rectification or linear vs non
linear.

I think the key point is that the usual "rectification" methods
require some kind of explicit or implicit (in the case of a heaters)
low pass filtering to remove the carrier component and keep the
modulation component. The Hilbert method describe by R. Lyons
requires no filtering and returns an exact result regardless of the
relationship between the carrier frequency and the modulation.

That is the beauty of it.

Hmm, interesting and a different question. It does remind me
of asking here about synchronous demodulation of AM signals,
such that you get the right result when the modulation index
is greater than one. I will guess that the Hilbert method
can also do that.

That is the problem I saw many years ago, if you applied a lot of
filtering to the diode detector to completely remove the 455 kHz IF
signal, you would loose some of the high frequency audio components.
Of course I was using simple RC filters, I know better now of
course.

But, to me, that is the ___fundamental__ advantage of the Hilbert
method over the "rectifier" methods.

-- glen

 

[Bret Cahill]

You can put the signal through almost any non-linear operation,

You can put the signal into the heater and measure the temperature.
Where is nonlinearity?

It would be hard to claim _that_ was "non linear" in even the least
sophisticated sense of the term.

That isn't the issue, however. The issue is rectification.

If some operation results in the same + sign of the magnitude of some
+/- signal then that operation could be broadly construed as
"rectification."

You can put the signal into a into a solenoid and measure the force
attracting a piece of ferrous material.

Same as the heater. The operation outputs a + magnitude for a +/-
signal.

Or, for that matter, the force
between two solenoids with the same current running in them.

There is a zillion of ways to measure AC without any nonlinearity or
rectification involved.

Maybe there are several if the wave form is known.


Bret Cahill

 

[Rick Lyons]

On Sat, 6 Nov 2010 00:29:42 +0000 (UTC), glen herrmannsfeldt
<gah@ugcs.caltech.edu> wrote:

In comp.dsp Bret Cahill <BretCahill@peoplepc.com> wrote:
(snip)

Poorly written OP. The goal is getting the amplitude _without_
rectification. Rectification" is to be very broadly construed and
includes anything that results in the final "signal" being positive at
all times.

Maybe peak to peak wil work if you know the wave form.

I still have my Heathkit VTVM, christmas present from when
I was in high school. The manual includes an explanation of
the form of rectifier used, and why the result is peak-to-peak.
Other than that, it seems unusual to rectify as peak-to-peak.

-- glen

Hi glen,
Good God!! When you mention a Heathkit VTVM
you strike a nerve with me. I had one of those,
with its cigar-sized probe and alligator
ground clip.

http://www.heathkit-museum.com/test/hvmv-7a.shtml

When I was in high school (yes I played on the
baseball team and got into trouble like any other
knuckleheaded high school student), I became
interested in electronics.

I mostly used my VTVM to test the filaments of
vacuum tubes from the old radios and televisions
that my neighbors threw away and gave to me.

Back then you could buy all sorts of electronic parts
from Radio Shack At that time Radio Shack was about
radios and electronics hobbyists. Now Radio Shack
is geared toward cell phones and digital cameras.
It's too bad, really too bad.

It's a shame but American teenage boys are now far
more interested in playing video games than
experimenting with electronics.

glen, are you old enough to remember the chintzy
little crystal radios that had a simple tuning coil,
capacitor (I think), diode, earphone, and NO BATTERY?
With those little crystal radios you could "pick
up" local AM radio while lying in your bed at night.

See Ya',
[-Rick-]

 

[Rich Grise]

Bret Cahill wrote:

Is there anyway to get an amplitude of an ac signal averaged over time
w/o some kind of rectification?

Yeah - the average of an AC signal is zero.

Hope This Helps!
Rich

 

[Baron]

glen herrmannsfeldt Inscribed thus:

In comp.dsp Vladimir Vassilevsky <nospam@nowhere.com> wrote:

Bret Cahill wrote:

Is there anyway to get an amplitude of an ac signal averaged over
time w/o some kind of rectification?

Sure. Connect the AC to a heater and measure the temperature.

This doesn't include the trivial, i.e., dc offsets or partial
cycles. The rectification could be analog, digital or software.

You need some non-linear operation, which may or may not be
considered rectification. I believe the heater/temperature
measurement has been used for RF power measurements for many years.

-- glen

Google "Bolometer".

--
Best Regards:
Baron.

 

[Tim Wescott]

On 11/05/2010 02:35 PM, Bret Cahill wrote:

In comp.dsp Vladimir Vassilevsky<nos...@nowhere.com> wrote:

Bret Cahill wrote:

Is there anyway to get an amplitude of an ac signal averaged over time
w/o some kind of rectification?

Sure. Connect the AC to a heater and measure the temperature.

This doesn't include the trivial, i.e., dc offsets or partial cycles.
The rectification could be analog, digital or software.

You need some non-linear operation, which may or may not be
considered rectification.

No nonlinear operations. Just multiply the AC by a synchronous reference.

I believe the heater/temperature
measurement has been used for RF power measurements for many years.

That doesn't do any rectification for sure.

Positive heat with a positive signal and positive heat with a negative
signal can only be considered a form of rectification.

Troll.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Tim Wescott]

On 11/05/2010 01:00 PM, Bret Cahill wrote:

Is there anyway to get an amplitude of an ac signal averaged over time
w/o some kind of rectification?

This doesn't include the trivial, i.e., dc offsets or partial cycles.

The rectification could be analog, digital or software.

Don't feed the troll

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Fred Marshall]

On 11/5/2010 5:26 PM, glen herrmannsfeldt wrote:

In comp.dsp Fred Marshall<fmarshall_xremove_the_xs@xacm.org> wrote:
(snip)

Multiplying by other than a constant or a stable periodic waveform is a
non-linear operation. Multiplying by a constant or a sinusoid or a sum
of sinusoids is a linear operation.... believe it or not.

Hmmm. As I understand it (longer ago than I remember) they used
to make rectifiers out of synchronous motor driven commutators.

That is, multiply by a square wave (sum of sines) of the appropriate
frequency. The result doesn't seem like a linear function of
the input anymore.

-- glen

Well, Jerry and I argued about this at length here some time ago. The
key is in the tests for linearity. It rather surprised me too and it
didn't "seem like a linear system" but it worked out.

In all these things we're talking about a 2-port situation and asking
whether the 2-port system is linear or not.

So, if the 2-port system is a 4-quadrant multiplier with a stable
sinusoidal input (which is not one of the "ports") then the result of a
signal on the "input" port is a sinusoid of amplitude proportional to
that input. And, if a different input is applied, same thing. And, if
the sum of those two inputs is applied, the output is the sum of the two
independent outputs.
etc.

Now, I must say that I was pulling from memory about the composite
sinusoidal modulating function .. but I think it still holds with that
being used instead of a simple sinusoid...

Fred

 

[Jasen Betts]

On 2010-11-05, Bret Cahill <Bret_E_Cahill@yahoo.com> wrote:

Is there anyway to get an amplitude of an ac signal averaged over time
w/o some kind of rectification?

Run it through a resistor an measure heat output. The result will be
proportional to the square of the amplitiude



--
ɹǝpun uʍop ɯoɹɟ sƃuıʇǝǝɹ⅁

 

[Jasen Betts]

On 2010-11-05, Bret Cahill <Bret_E_Cahill@yahoo.com> wrote:

In comp.dsp Vladimir Vassilevsky <nos...@nowhere.com> wrote:

Bret Cahill wrote:

Is there anyway to get an amplitude of an ac signal averaged over time
w/o some kind of rectification?

Sure. Connect the AC to a heater and measure the temperature.

This doesn't include the trivial, i.e., dc offsets or partial cycles.
The rectification could be analog, digital or software.

You need some non-linear operation,  which may or may not be
considered rectification.

No nonlinear operations. Just multiply the AC by a synchronous reference.

I believe the heater/temperature
measurement has been used for RF power measurements for many years.

That doesn't do any rectification for sure.

Positive heat with a positive signal and positive heat with a negative
signal can only be considered a form of rectification.

In that case the answer is "no"

--
ɹǝpun uʍop ɯoɹɟ sƃuıʇǝǝɹ⅁

 

[Jasen Betts]

On 2010-11-05, Bret Cahill <BretCahill@peoplepc.com> wrote:

The goal is getting the amplitude _without_
rectification. Rectification" is to be very broadly construed and
includes anything that results in the final "signal" being positive at
all times.

show me a signal with negative amplitude.

--
ɹǝpun uʍop ɯoɹɟ sƃuıʇǝǝɹ⅁

 

[Bob Masta]

On Sat, 06 Nov 2010 09:52:02 -0700, Fred Marshall
<fmarshall_xremove_the_xs@xacm.org> wrote:

On 11/5/2010 5:26 PM, glen herrmannsfeldt wrote:
In comp.dsp Fred Marshall<fmarshall_xremove_the_xs@xacm.org> wrote:
(snip)

Multiplying by other than a constant or a stable periodic waveform is a
non-linear operation. Multiplying by a constant or a sinusoid or a sum
of sinusoids is a linear operation.... believe it or not.

Hmmm. As I understand it (longer ago than I remember) they used
to make rectifiers out of synchronous motor driven commutators.

That is, multiply by a square wave (sum of sines) of the appropriate
frequency. The result doesn't seem like a linear function of
the input anymore.

-- glen

Well, Jerry and I argued about this at length here some time ago. The
key is in the tests for linearity. It rather surprised me too and it
didn't "seem like a linear system" but it worked out.

In all these things we're talking about a 2-port situation and asking
whether the 2-port system is linear or not.

So, if the 2-port system is a 4-quadrant multiplier with a stable
sinusoidal input (which is not one of the "ports") then the result of a
signal on the "input" port is a sinusoid of amplitude proportional to
that input. And, if a different input is applied, same thing. And, if
the sum of those two inputs is applied, the output is the sum of the two
independent outputs.
etc.

Now, I must say that I was pulling from memory about the composite
sinusoidal modulating function .. but I think it still holds with that
being used instead of a simple sinusoid...

I think this depends on what you mean by "linear". Most of
the time, IMHO, we mean "no new frequencies produced in the
output". Multiplying two sinusoids violates this, because
you end up with sum and difference frequencies.

Think about amplifiers. We talk about "nonlinear
distortion" when we get new frequency components (THD, IMD,
slew limiting, etc), while "linear distortion" (which is a
rarely used term) means only changes in amplitudes or phases
of the original frequency components.

Best regards,


Bob Masta

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[Fred Abse]

On Sun, 07 Nov 2010 04:22:16 +0000, Jasen Betts wrote:

show me a signal with negative amplitude.

a sin x at x>pi<2*pi

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)