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From Friday, April 19th (11:00 PM CDT) through Saturday, April 20th (2:00 PM CDT), 2024, ni.com will undergo system upgrades that may result in temporary service interruption.
We appreciate your patience as we improve our online experience.
08-22-2014 08:19 AM
I'm using PXI-4071 and a PXIe-2575 in handshaking mode with a scan list.
The DMM is measuring current and the MUX is in 1x196 mode.
When running the scan list, I rarely (randomly) get a very small measurement in the nA to uA (when it should be 4-20mA). I'll run the scan list again and that channel will be correct, so it doesn't seem to correspond to a channel.
I've tried increasing the settling time of both the DMM and the MUX, but neither have had any effect.
Any help would be great.
Thanks,
Caleb Swieson
Solved! Go to Solution.
08-22-2014 10:02 AM
One more point. I am reading the measurements from the DMM while it is still running through the scan list (so I can process the data as it's being measured). At the moment this is where I feel like the issue might be, but have no idea if and why that would be.
08-22-2014 10:51 AM
Cswieson,
Is the relay board relatively old? If a board is close to end of life, there is a chance that the relay will sporatically not close and/or open. If the relay is stuck open, the DMM might measure very low current because no current is flowing (and only noise is coming through).
08-22-2014 11:03 AM
Hi Frank,
No, the board is only a year old. I checked the relay counts and the most counts is still <10,000. Most are less than 1000.
Caleb
08-28-2014 11:22 AM
After further testing, we have determined it was actually the devices being measured that were outputting the very small currents. So it wasn't the hardwares' fault. Whoops
08-28-2014 02:07 PM
Thanks for following up, cswieson! I'm glad you were able to find the root of the issue.