Problem with analog input on PCI-6025E

[bray]

I have recently run into a problem with the analog input channels on a PCI-6025E. I have a SCB-68 connected to it via a SH1006868 (the MIO-16 half of the cable), and am trying to use the cold junction compensator for a thermocouple feedback control.

I loaded the example VI "Continuous Thermocouple Measurement" and connected a thermocouple for single ended operation on AIch1. The temp in the program reads 910C. In the MAX test panel, the signal in AIch1 increases very quickly and then stays maxed out at 10V. I also tried using a DC power supply to input a simple signal, but there's no response.

Any suggestions? Could this maybe be a grounding problem?

Brian

[AVR]

Since you are unable to read a DC power supply on the channel, I would suggest that you verify the cabling and hookup. The rising and saturated voltage response is typical of an open (unconnected) channel. If you simply short the input (connect the AI input to the ground reference connector) you should read zero volts. If you do not, I suggest that the cables and terminal blocks are not properly connected - or worse, something is now wrong with the DAQ card.

[bray]

I shorted the input to the AI channel, and the signal still drifts around a lot. As I mentioned, the output channels on the board seem to be working fine. If this is a problem with the DAQ card, do you think this is something that would get picked up by the online E-series diagnostic tool? I ran that and didn't have a failure with the AI channels.

[AVR]

I have never used the online diagnostics tools so I can not address the issue of what the tool can detect. Since a dead short on the input does not force the recorded voltage to zero (or at least very close in the 1-2 millivolt range, I would suspect that some portion of the input circuitry is damaged. I would suggest that you try to input data on another channel. All of the inputs are put through one A/D convertor through a multiplexer. Perhaps only the terminal connectors on channel 1 are deffective. If all of the channels exhibit the same drifting characteristics, I would suspect that the AI circuitry is damaged.