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I am using a SCXI-1127 module in independent mode to do a 4-wire resistance measurement (using a PXI-4070 DMM). I am expecting about 3 Ohms. When I first power on the station and make the measurement, the resistance is upward of 15 Ohms. I can hook up an external DMM to the 4070 leads and watch the resistance slowly decrease to the expected 3 Ohms. This is only happening with one channel in the 1127. I had a similar problem with another 1127 (I am running 8 of the 1127 modules), so I switched it out with one that is not used for resistance measurements and the problem went away. I can't switch this one out since the rest are used for resistance. So, my question is, is this a sign that the module is starting to fail? The module is about 8 years old. We had another test stand that had the same behavior. We replaced the suspect module with a new one and the problem went away. Anyone have experence in this or know if the module is failing?
The behavior you are seeing on your SCXI-1127 is definitely expected behavior as your device ages. If you look on page 2 of the SCXI 1127 manual, it mentions that as the relay ages, the path resistance rises rapidly above 2 Ohms. Since your card is older, you are probably getting close the the lifetime expected cycle count before failure. Because of this, you may want to replace the relay for better performance.
