Perhaps the low pass filtering on the cards is not the same. You may be seeing the effects of some "high frequency" noise causing aliasing which is perceived as a variation in temperature. Check the input voltages using an oscilloscope. Measure the voltage on each leg of the differential inputs separately as the scope will be grounded. Also verify that the common mode voltage on the differential inputs is within specs.
----------------original question------------------ I have an application with many temperature readings. I have a dedicated SCXI 1102 card for most of these but I have not got enough channels so I have been using an SCXI 1100 card for the spillover. I noticed that the readings I was getting for this card were fluctuating a lot, much more than they did when I checked the signal in MAX. Also, I noticed that when I acquired from the 1100 card in a calibration routine elsewhere in my application, the signal wasn�t fluctuating at all. The only difference between the calibration routine and the main application is that in the main application I am acquiring over 40 channels whereas in the calibration routine I am taking only 3 or 4 at a time. ------------------------------------------------------ Lewis Drake Process Automation Corporation Belle Mead, NJ 908 359-1011 www.processauto.com
