Noise Reduction

[dflynn]

I'm using  a cDAQ-9174 and NI 9237 powered by a NI PS-15 power supply to take pressure measurements. There is significant noise in all of my pressure measurements, including in slots that are not plugged in (red and yellow lines in "block" attachment). The "zero pressure" attachment shows what the DAQ is reading at zero pressure. Is there a filter built into LabVIEW that I can use to smooth out my signal?

[BertMcMahan]

There are some filters in the "Signal Processing" palette that you can use. I don't think they work on dynamic data though, so you'll have to either convert your data or just use regular DAQmx functions (Help -> Find Examples, there are lots of good ones).

Unconnected lines are always going to be noisy as there is nothing specifically setting the voltage to any value, so it'll just bounce all over the place.

[Bob_Schor]

Your Pressure Settings picture suggests you are sampling at 25 kHz.  How fast do you expect Pressure to be changing?

Looking at some other of your pictures, it looks like you have "noise" with a lot of energy at 120 Hz.  This is a suspicious number, being twice 60 Hz, which is ubiquitous around here (but, perhaps, not as much in Europe).  This is called (you guessed it!) "noise", and even a non-engineer such as I know that you want to shield your input wires, differential is often better than single ended, and unused terminals should be wired to Analog Ground (unless testing shows that makes things a lot worse, but then you'd have other problems ...).

Bob Schor

[dflynn]

When I have the other two channels connected for testing I do make full use of the 25 kHz sampling... I did not know about unused terminals needing to be connected to a ground, that could be a part of my problem. Maybe my best bet would be to make a second program for when the other channels are not in use and turn down the sampling rate as well. I'll start there then try replacing my old wiring, thanks!