Electronic – Variable Input Voltage Power Measurement

audiopower-measurement

I've looked around the site for suggestions, but think this question is a unique one and would love some conversation.

I need a method to measure the average power in to a transducer.

This method must

  1. Be able to measure the power of complex input waveforms (audio input, in this case)
  2. Be able to measure the power of a signal oscillating around a DC voltage
  3. Be able to measure the power of a signal oscillating around 0 V (AC)
  4. Be able to measure the power of a signal which oscillates around some DC value, and not fail when the oscillation is of such a magnitude that portions of the signal fall below 0 V

The general parameters of the waveforms I'm measuring are

  • Audio, with and without DC bias
  • Chirps, with and without DC bias
  • Single frequencies, with and without DC bias

Before you ask, the DC bias is absolutely necessary! The physics of the devices for which I must determine the average power input require that I test signals with and without a bias.

In sum, I need a method of measurement which can accept voltage and current frequencies from 0-25kHz, is minimally invasive, is accurate to within a hundredth of a Watt (tenth might be okay too), and can handle voltages both with and without a DC bias that have peak to peak values from 0.1 V – 50 V.

An idea I've been given is that I could use transformers to remove the bias, measure the bias and the alternating component, and add them to obtain the average power.

Thanks in advance for any advice you can give!

Best Answer

I think that by sampling the signal and integrating by SW you can achieve the results you want. Here comes the questions: What ADC resolution and what sampling rate. What quality of filter will you provide to concentrate on your required BW. Audio filters can be complicated because of their very narrow BW. The waveform type (with, without DC, etc.) is no issue for an integrating algorithm. It is only and issue for the analog front-end that has to condition the signal to the ADC range. Another limitations I see are the achievable accuracy, how to calibrate your HW/SW, and how to adapt the instrument to the range you specified, be it via mechanical/electronic attenuators and with or without auto-ranging.

Each option you want to add will be another complication of the SW. So, where to draw the line to keep it simple? Not easy to say.

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