Amplitude Time Ave. w/o Rectification

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.


Bret Cahill

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?


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

On Nov 5, 4:00&#4294967295;pm, Bret Cahill <Bret_E_Cah...@yahoo.com> 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.
>
> Bret Cahill

See "Understanding DSP" by R Lyons  p 366 of the second edition..

Use a Hilbert to get Real  and imaginary components of the signal
then, the envelope is found as the SQRT (R^2+i^2).

No rectification and no low pass filtering is needed.

I found this fascinating becasue as a kid playing with AM radios, i
began to understand the limitations of a diode detector and this is
the elegant solution...

Mark

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

glen herrmannsfeldt wrote:

> 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. 

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.

VLV

> > 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, &#4294967295;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.


Bret Cahill

> > 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.
>
> > Bret Cahill
>
> See "Understanding DSP" by R Lyons �p 366 of the second edition..
>
> Use a Hilbert to get Real �and imaginary components of the signal
> then, the envelope is found as the SQRT (R^2+i^2).

Sqrt of sum of squares = absolute value = rectification.

> No rectification and no low pass filtering is needed.
>
> I found this fascinating becasue as a kid playing with AM radios, i
> began to understand the limitations of a diode detector and this is
> the elegant solution...

Maybe a difference measurement of peak to peak of a known waveform
wouldn't be considered rectification.


Bret Cahill

In comp.dsp Vladimir Vassilevsky <nospam@nowhere.com> wrote:
(snip regarding rectiification, and I wrote)

>> 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.

Multiplying by other than a constant is a non-linear operation.
 
>> I believe the heater/temperature
>> measurement has been used for RF power measurements for many years.
 
> That doesn't do any rectification for sure.

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.

-- glen

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.

1. Take 3 consequent samples x[0],x[1],x[2]
2. Solve the system of equations x[i] = A sin(Wt + Fi)
3. Now you know A, W, and Fi

> > 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.
>
> > Bret Cahill
>
> You need a precision rectifier..
> � �couple of op-amps and maybe 1 diode ..
>
> http://sound.westhost.com/appnotes/an001.htm


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.


Bret Cahill