measuring change in voltage amplitude

[pedram]

Hi I am using a DAQ card and a card box to acquire an analogue signal from an IR sensor. I used the “cont Acq to spreadsheet.vi ” example to start with and I modified pats of it to get the outputs I needed. Up to this stage it works fine.
My signal has 2Hz frequency with maximum amplitude of around 6.7 V the absolute voltage amplitude drops as the as result of IR sensing a substance. I want to be able to detect this drop in the amplitude and the minimum value it reaches as a function of time and possibly plot it. So it is not just the drop that matters but how rapidly it happens and how long it takes is the main objective of the program. I hope you understand what I meant and thank you I have attached the file as i
t it a bit complicated for me to explain what happens in the program.

[Dennis_Knutson]

There is a function called Transition Measurements 1 chan.vi in the Analyze>Waveform Measurements palette. You specify reference levels and rising and falling edge and it outputs fall time, slew rate, etc. If I understand your problem correctly, this sounds like what you're trying to measure.