Speed of Thermistor Measurements With Multiple PXI-4351 Coards

[dilkgeet]

I have Labview 8.2 controlling a PXI chassis with 4 PXI-4351 boards. All four boards will be connected to 16 thermistors, and I need to read these as fast as possible.  Currently, I have written a VI to read off the temperatures from 1 4351 board.  This VI is attached below.  I then run 2 copies of this VI concurrently to read the thermistors from 2 4351 boards.  If I set the number of scans to some number like 20, then the time taken for each VI to run is about 1.5 sec.  However, then the VI stops (presumably after all 20 scans are done).   This 1.5 sec is an acceptable time, but we need the VI to run continously without stopping.  How do I do this? And is there any way to speed up the program even further? Thanks

[stilly32]

Hi,

It looks like your program could be filtering out an error message, but your error is still stopping your program. 

If you connect the error cluster through in the enabled case, do you get an error after you exit? If so, what is it (Screen shots are helpful)? Just to check, is the data that you read correct? Also, I don't know that your timing is that accurate. You don't control when the tick count is taken, so it may occur before, during or after that AI Read. To get a better idea of the time it takes you should probably use the tick count at the end of your loop, possibly in the enabled state of the Diagram Disable Structure.  

Hope this helps, please post back and we'll get you up and running.

Cheers,

Andrew S

National Instruments

Message Edited by stilly32 on 03-07-2007 01:08 PM

[AnalogKid2DigitalMan]

Do you know the actual response time of your thermistors? Unless they are very small, they are probably fairly 'slow' (100's of milliseconds to seconds). You should only need to sample 5 to 10 times as fast as their reponse time to get valid data. Any faster and you are probably generating too much data.

Just a thought to consider.