best measurement method ?

[carlmbecker]

Hi all.

What would be the best measurement method for the following impedance measurement :-

I am injecting a signal of a few Hz (10Hz) up to a few MHz (3MHz) in increments of a few Hz. I then measure the injected signal and the returned signal which varies in amplitude depending on the frequency (device under test resembles a complex impedance with LRC components). This is performed in steps (1) first inject 10Hz - do measurements on both signals. Process the data then (2) increment signal .....

Time is not an issue.

I would ultimately like phase and magnitude (info) between the injected and returned signal.

I could use various ways of extracting this info but looking for advice from people more familiar with DSP techniques. (FFT, FIR only etc.....)


Thanks in advance

 

[FvM]

For low frequency problems as your application, the terms injected and returned signal should be better replaced by voltage and current in my opinion. You inject a current and measure voltage or vice versa.

You can refer to the design of state-of-the-art LCR meters, how they achieve a precise measurement. I think, the most simple and straightforward method is synchronous quadrature demodulation. FFT is a more general approach, although I don't exactly see an advantage for this application.

For the possible system topology, should also take a look at the Analog Devices AD5933, a signal chip DSP impedance analyzer. It uses FFT.

 

[carlmbecker]

Thanks FvM points noted but because I have access to both input and output signals I would prefer the simpler way.