cDAQ 9237 slow to read data

[crelf]

Hi All,

   One of my clients has a cDAQ chassis with 4 x 9215's and 2 x 9237's - he's using a relatively generic DAQ utility that is acquiring a handful of differential channels on the 9215's without a problem, but as soon as he adds a strain channel on one of the 9237's, the systems grinds to a halt, as it can't read the data from the 9237 fast enough.  He's tried sampling rates from 1Hz to 100Hz, and although the time it takes to fill the buffer varies, it still can't read it fast enough for some reason.  I know I'm not being particulariy coherent here, but I'm just fishing for any lightbulbs going off anywhere 🙂

cheers,

Chris

[KyleBryson]

Chris,

Are you using a third-party utility that treats the two modules as different devices, creates two different tasks, and then starts and stops them and alternates between the modules?  That would be a problem...and one such utility definitely sets off a lightbulb.

I'd recommend one of many National Instruments development platforms and NI-DAQmx for best performance with CompactDAQ.

Regards,
Kyle

[KyleBryson]

Chris,

Also note that the 9237 cannot run as slow as 100 Hz.  See the first two posts by Salvador Santolucito in this thread:

http://forums.ni.com/ni/board/message?board.id=250&message.id=24251

for an explanation of the minimum rate available on the 9237.

Regards,
Kyle

Message Edited by KyleBryson on 01-12-2007 05:35 PM

[crelf]

So it's possible that the buffer is filling up because the 9237 is acquiring faster than the other devices - that's certainly a lightbulb moment 🙂  Determinism at the lower level isn't an important factor here, so I'll just adjust the software to clear the buffer everytime it reads acorss the chassis.  Thanks for your help!

[daquiry]

Hi,

I created a VI out of a VI logger NI-DAQmx task to slow down the 9237.  The problem is that I get a file every minute becuase I'm running the whole thing inside a a while loop that runs once a minute.  Is it possible to modify the code so that I write multiple times to a single file, instead of writing multiple files?

[Elijah_K]

 

Message Edited by Elijah K on 03-15-2007 12:03 AM

[Elijah_K]

I'm afraid that this is a limitation of VI Logger.  Every set of acquired data is kept seperate.  I recommend you check in to Signal Express 2.0.  It's newer and easier to use than VI Logger and offers more advanced functionality