Setting 9219 sample rate

[ECS]

We are running a compactDAQ 9172 chassis with a 9205 and two 9219 modules.  The 9219s are configured to measure thermocouples.  I found a thread attempting to describe how to set the sample rate for the 9219 but the picture of the code wouldn't load.  From the text description I attempted to set the Channel Properties for these modules to 14712 to give the fastest sample rate (see attached code).  The loop will still only run at about 750 ms w/o being 'late'.  I'd like to run at 250 ms.  The loop will run much faster with the thermocouple (9219) channels removed from the task, so I think the issue is the 9219 channel setup. 

Thanks for your help,

Chuck

[Brad_K]

Hi Chuck,

There is a bug in DAQmx that causes NI 9219 on-demand thermocouple channels to always use the "high resolution" ADC timing mode when built-in CJC is enabled. It has been reported to R&D as CAR 4BC3NIEV. The workaround is to configure a sample clock, by either calling DAQmx Timing.vi or selecting "N Samples" or "Continuous Samples" for the DAQ Assistant's "Acquisition Mode" setting.

The way you're using the DAQmx Channel property node to set the AI.ADCTimingMode property is almost right but you need to wire the DAQmx Channel to the same DAQmx Task reference that you're passing to DAQmx Start.vi, not a separate DAQmx Task reference. I'll attach a picture (assuming that "T NOx CTR" and such are the names of channels in the "CarDAQ" task):



(By the way, if you right click on the property node input and select Create»Constant, LabVIEW will put a ring constant on your diagram so that you don't have to look up the numbers.)

Brad

Message Edited by Brad K on 10-31-2007 04:22 PM

[ECS]

Thanks Brad!

Chuck

[Matthew_W]

 Hi Chuck,

 There's another KB here that deals with that issue. What Brad has said (thank you!) is absolutely correct.

 Best regards,

MatthewW
Applications Engineer
National Instruments