11-11-2019 08:58 AM
I am using the NI USB_6001 DAQ. By wiring the DAQ to itself (AI 0+ & AI 4-) and running a differential measurement on the device itself, I am getting a noise reading that switches between -0.0002 V and -0.0015 V (picture attached). Resulting in -1.3 mV noise being in the device alone. When trying to get a reading of 5V from a power supply I am getting readings that switch between 4.9891 V and 4.9879 V (picture attached). Again that ~1.3 mV switching.
Is there a way to measure the device noise and filter it out from the voltage read?
I am trying to read as close to a flat DC line as possible.
Is there a way, perhaps in LabView, to set up something that will measure the internal noise by wiring a short wire from pins AI 3 and AI 7, running a differential measurement on those pins to get the device noise with no voltage being supplied. And then to read pins AI 0 and AI 4 and subtract the device noise from the results of the voltage read?
I have read the Field Wiring and Noise Considerations for Analog Signals a couple of times and already aware that I am using a Grounded signal source (power supply) and a differential measuring system (DAQ). I know that this can cause a Ground-loop noise to be present. I have tried numerous different wires and different wire lengths with no change. I also am aware that there is some miniscule noise variation when my laptop charger is plugged in vs not plugged in.
Any insight would be greatly appreciated.
11-11-2019 01:20 PM
Your device supports only a 20V range from -10 to +10 VDC. It digitizes with 14 bits. 20V / (2^14) ~= 0.0012 V.
What you're seeing is 1 bit worth of quantization noise in the LSB of your A/D conversion. I don't know if you're gonna be able to do better than that.
If I *had* to try, I'd oversample and average. The theory is that as the LSB toggles back and forth, a mean will weight the two values proportionally to the time spent at each.
-Kevin P