Dear all,
I have an application where signals from two thermalcouples are introduced into SCXI-1125 in differential mode by SCXI-1327, and then flow into a PCIe-6351 board.
There is also an IGBT in the system. The whole system works so well one month ago and the configuration of the system keeps unchanged. Now, if the plug of the IGBT is unconnected signal introduced into any channel can be sampled with little noise; but if we connect the plug, all signals terminated in AI 1 to AI 7 shows remarkably increased noise, while signal terminated in AI 0 shows no change as before.
The thermal couple wires have small impedance of about 7 ohm. We tried twisted wires but that does not work. I am surprised that AI 0 keeps unaffected with other channels affected. This phenomenon also has nothing to do with whether the signal is grounded or not.
Is there possibility that our SCXI-1327 and SCXI-1125 have some problem now? Thank you for any suggestion.
Su
