Barry, The SCXI 1100 only has a single filter which is after the multiplexer. To obtain a filtered output for each channel, you must stay on that channel long enough for the filter to settle. If you are only looking at a single channel you get a nice filtered output, but if you are multiplexing you get a mess at high sample rates. The total sampling rate must be lower than the selected filter frequency. With the 10 kHz filter you can sample a total of 6.6 kS/s. If you want to use the 4 Hz filter, you can only sample at 3 samples per second!!! Take a look at the specs on NI's website.
The SCXI 1102 has a filter on each channel, so even when you are multiplexing you get a clean filtered value for each channel. I have yet to find an application where I would want to use the 1100 instead of the 1102. My advice would be to replace the 1100 with an 1102, but that is an expensive option. Turning off the filter may improve the accuracy of the data, but it will be noisy. I would use the lowest frequency filter possible that works with your sampling rate. Check the specs to figure that out. Bruce ------------------------------------------ Bruce Ammons Ammons Engineering www.ammonsengineering.com (810) 687-4288 Phone (810) 687-6202 Fax -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Barry Brophy Sent: Monday, May 24, 2004 11:01 AM To: [EMAIL PROTECTED] Subject: Question to Info-LabVIEW Digest LabVIEW SCXI 1100 anomaly Dear all, I have run into a truly bizarre anomaly when reading from an SCXI 1100 card with labview 6.1. I have been using labview for over 4 years and have never seen anything like this. I wonder if anyone can help me. 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. The code I am using is exactly the same in the two locations. only the number of channels being acquired is different. The signals from the 1100 are affected but the signals from the 1102 are fine in both routines. I have repeated this problem in two different locations. I have also noticed that it affects pressure signals on the SCXI 1100 as well. Can anyone offer me any advice on this? Regards, Barry Brophy
