I am getting an 80 mV error on only 1 channel of my AT-MIO card.

[tiberius]

I have an AT-MIO-16DE-10 card that is configured to read 16 RSE inputs - eleven of them the same manufacture and make of temperature probe. All the probes are part of the same system, which is currently inactive, so all probes should read virtually the same thing. However, one of the eleven reads 80 mV more than the rest. This is a problem, as this equates to about 4 degrees C.

Here are the steps I have taken: I have measured all incoming signals for these probes 3 ways - (1) with a DMM at the input, (2) using the NI-DAQ Config test program, and (3) using my final VI, which is nothing more than the basic AI Read VI that comes with LabVIEW. The input channels are labeled 0:15, so all 16 channels are
read at once with the same VI and fed into a 2D matrix. All three types of measurements for all channels are normal and agree with one another EXCEPT for the VI measurement for the channel I am referring to. In this one case, the reading is 80 mV higher than the rest. Note that the DMM and NI-DAQ readings are fine for this channel.

The first thing I did was hook up a dc power supply to the channel in question. After this, the channel read perfectly in the VI, so I assumed the problem was a defective probe.

Next, I switched two of the probes. I connected one that had worked on another channel to the defective channel and vice versa. Unfortunately, the same channel (now with the known good probe) still read 80 mV above what it should.

It is my understanding from the manual that the AT-MIO-16DE-10 does not have an interior jumpers for the channels, so I am at a total loss as to what is happening. Does anyone have any other suggestions?

[JoshuaP]

There are a couple of different issues that could result in this kind of offset. My first question would be how long has it been since you had this device calibrated. It is possible that the AT-MIO-16DE-10 is out of calibration. Most people take the time to send there DMMs off for calibration, but never sent there DAQ cards off, even though they use and act exactly the same and therefore both need to be calibrated.

The second issue is that it could be a grounding problem. Since you are using RSE it is very easy to create grounding loops that result in this kind of offset. Is it possible that this one probe is getting its power from a difference source or outlet than the other probes, which results in a grounding difference?

Have you tried wiring the same p
robe to its original channel and this channel at the same time? This would remove the grounding loop and allow you to test the bad channel against a good channel to see if there is a difference.

Finally, if you are modifying the range on AI Config, make sure you modify each entry in the array for each channel and not just the first one. This makes it very easy to set a gain for the first channel and use the defaults for all of the other channels.

I hope this helps.

Joshua