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I am having trouble with my PXI-2520 relay module. I am using it to control power to a few external devices (28V at 0.5A). From the spec this is within acceptable ranges. I have noticed that a number of relays appear to be stuck in the closed position (power is still getting to some devices). Using NI Switch soft front panel or running a C program (using NI DAQmx) will not open the relays. The C program is returning success and the test panel is showing the relays are open but they are not. I have tried restarting the PXI controller, resetting the module, performing the self test in MAX and nothing is working. This is a relatively new purchase, the relay count is very low (around 40). Are the relays already damaged? Is there any way to get these relays to respond?
Depending on type of load being switched it is possible that the relays have already been damaged. If the load has an inrush that exceeds the rating of the contacts this can cause this type of issue. Conversely they can be welded closed by the act of opening if the signal you are switching is a constant current source. As the resistance of the path increases the load increases it's output to maintain the required current there by exceeding the rated capacity of the relay.
