Measuring Amplitude of AC signals

[Kingpin094]

What is a good method of measuring the Peak amplitude ot an AC signal?

Some paramters.
1) Signals can be Sine, triangle or square waves
2) Frequency from 1Hz to ~1MHz

Methods considered:
1) Rectification and then measure smoothed dc value.
2) Peak detector with reset

Are there any other ways to measure Amplitude of ac signal? It only needs to be
Gnd to peak a.k.a. single ended amplitude.

Thanks
kingpin094

 

[mstechca]

If I can remember correctly, the amplitude is the height of the wave (bottom to top measurement).

An easy (and probably a ridiculous) way to measure amplitude is to hook the device to a speaker.

For example, if you made a simple oscillator, and you want the approximate amplitude, hook it to a speaker, and then listen.

The louder the sound, the higher the amplitude.

If you don't want to use the speaker, then use an LED. The brighter the LED, the higher the amplitude.

As for exact measurements, since I'm a guy without many tools, I can't really help you for that one.

 

[instruite]

Hi Kingpin094
Do you want to measure the amplitude within a circuit or using some tools?
If you want to measure with tool then you can use oscilloscope.
If you have to do in circuit measurment then
among the methods you suggested
1) You cannot use this metod to detect peak because smoothed DC value will not be equal to the the Peak amplitude of the AC signal, it will always be less.
2) This method will be good to measure the peak value but for reset of the peak value you will have to detect the zero value also.

 

[Russlk]

If you rectify and filter ( average) the waveform, you will have to know the waveform and comput the peak because the average is different, depending on the waveform.

The peak detector and reset will work in any case and is the best solution.

 

[Kingpin094]

After some PSpice simulation I have come up with the following circuit that seams to work.
The only thing is that it only works accuratly for frequencie less then ~50kHz.


The output is the voltage across C1.

Which part of the circuit is the limiting factor?
Should the capacitor ba bigger or smaller?

Is there a good way to use a digital signal to short th output to ground?
Tried using a 2N2222A but it made the output fluctuate.
Would a mosfet be a better choice.

The circuit is part of a function generator. I am trying to measrue the waveform frequency and amplitude
for display on a character LCD. So the circuit needs to be able to be read by the A2D of a PIC 16F876A.

Thanks
kingpin094

 

[instruite]

The limiting factor in the circuit for frequency response is the capacitor
If you reduce the value of capacitor the input frequency can be increased

its better to put a current limiting resistor in the place of diode as this will be fed to the microcontroller input.

There is also a IC available for peak detection with reset and hold mode
Check the analog devices website for IC PKD01

or You can check the below links for other circuit options

**broken link removed**
https://www.electro-tech-online.com/custompdfs/2005/06/an1097.pdf
**broken link removed**

Just google the web for peak detector and you will find many more circuits