We are using this PXI-6254 board as an Analog input board. But we are facing a signal drift problem. We did some lab tests by connecting external battery signal (3vdc) to first four channels, Ch-0 to Ch-4 of PXI-6254 board in differential mode for the range +/-10Vdc and measured and recorded the signal continuously over 3 nights period. Data we collected, shows a steady signal drift (climb) over the period of time. Attached is the picture showing signal drift in graph format.
We have a DMM connected to the battery and it is not drifting (climbing).
Is this drift normal? Should it stop at some point?
Do you have bias resistors in place? Since the battery is a floating signal source, bias currents may be causing DC drift.
Take a look at the Analog Input Connections table in the Field Wiring and Noise Considerations document.
What sampling rate are you using?
Based on the M Series user manual, in the Connecting Floating Signal Sources section, differential connections are recommended for low level input signals (under 1V) and NRSE connections are recommended for higher level signals (above 1V). Have you seen the same behavior in this configuration? This same guideline is found in the Field Wiring and Noise Considerations document, under the table.
May I also ask, what the DMM was reading over the course of this period?
The drift is 3mV about 0.1% , have you recorded the internal temperature of the DAQ?
(and of the battery?)
While having a look at http://sine.ni.com/ds/app/doc/p/id/ds-22/lang/en
(more in the specs) @ +/-10V the AbsoluteAccuracy = 1920 µV
giving another coarse 1mV for external temperature drifts ... looks reasonable ....
So all what you can trust is about 14bit....