Transfer Function, Impulse Response and Impedance of a DUT to a Linear Sweep (Chirp) employing FFT and IFFT

[Daniel Akeju]

Hello,

I am new to LabVIEW and relatively new to the forum. I have a project I'm working on. So far, I have worked a little in MATLAB to learn more about how to tackle the issue in LabVIEW. Allow me to summarize my plans.

I will love to find H(f) for a DUT and consequently the Impedance Z(f) at different frequencies over a range (sweep). For simplicity, I assumed a capacitor to be the DUT. In MATLAB, I was able to code the chirp to sweep from 20 Hz to 20 kHz while obtaining the Y(f) and thus H(f) for the DUT (I used an equation to represent the behavior of the DUT). I will love to accomplish this in LabVIEW.

My anticipation is that I will generate a linear chirp then measure the voltage across the DUT then LabVIEW would perform FFT for both the input and output signals and then get the ratio to obtain H(f) at individual frequencies over the range. With H(f), Z(f) will be determined for all the frequencies also.

With all that I have said, my main concern is the FFT/IFFT portion and finding the most effective way to generate the chirp. Please help me out with suggestions.

Attached is a reference paper that highlights the idea of obtaining Transfer Function from a Sweep.

Thank you,

Daniel

[Kyle_K]

Hey Daniel,

Everything you want can be found in the Signal Processing Toolkit. It can be found on your Functions Palette. If you cannot find it, you need to install it from our website www.ni.com/downloads and navigate your way to the drivers. Within this toolkit, it has a VI for FFT, IFFT, and Chirp generation. Take a look! 

If you have any other qestions, feel free to ask.

Kyle K.