Hello MVK,
If by "open channel" you mean that you're disconnecting the sensor and leaving the channel unconnected during a scan this is probably expected behavior. When you scan a channel that doesn't have anything connected to it then the readings may be unpredictable. If the unconnected channel drifts to a voltage outside of the input range for the data acquisition (DAQ) card then the settling time will increase. If the settling time increases then you may see this affect readings on adjacent channels. Here is a KnowlegeBase article that explains this in further detail: Why Do I Experience Incorrect Readings When Sampling Open SCXI Channels?
It sounds like this is likely the issue you've seen before, and it may not have come up before because the unconnected channels weren't drifting as much. The further these channels drift the longer the settling time so it’s possible it wasn't drifting as far before so the settling time was still within an acceptable range where it didn't affect adjacent channels.
If you want to test if this is this is the case then you can disconnect ("open") channel 1 and remove it from the scan list. If you don't scan any open channels then the connected channels should all read correctly.
I hope this helps, if you meant something else by "open" please post back with more information on what you're doing.
Cheers,
Brooks
