Slow loop times with 6024E and LV2009

[Steve2571]

Hello all,

I have searched the forums back and forth, in addtion to the knowledge base, but I am still confused as to the slow loop times I am experiencing.  I have a 6024e PCMCIA DAQ card with a very simple VI created in LV 2009.  I am using the DAQ Assistant to collect 1 thermocouple channel on a SCXI Chassis 32 channel thermocouple module.

The problem is that the loop times in labview is about 3 seconds.  The DAQ Assistant acquisition mode is set to "on demand".  The target sample rate is about 1 to 2 samples per second.  I have read in previous posts that the repeated creation of the task using the DAQ Assistant with the acquisition mode set to "on-demand" can slow things down.

What really has me confused is that using this exact same method of setting the DAQ Assistant acquisition mode to "on-demand" has worked fine on the same hardware when using one of the earlier v8 versions of LabView.  I don't understand what has changed and why the loop times are so much slower.  I planned to pull the newest LV2009 off the computer and put a previous v8 version on just to confirm my observations.  In addition, I pulled up a copy of the VI that was written in one of the v8.x versions and it used the DAQ Assitants with the acquisition mode set to "on-demand" and had a loop time of 0.100 seconds.

Any help would be appreciated.  I have been working on this all day today with no sucess.

Thanks in advance,

Steve

[HeatherBaker]

Hi Steve,

There is a LabVIEW 2009 patch available for download if you have not done so already.  This may not fix the problem; however, I wanted to make it known that it does exist.  How are you determining the loop time?  Did you try multiple blank VIs in LV 2009 to ensure it was not a corrupt VI?  What version of the DAQmx driver are you using?

[Steve2571]

H_baker,

I did have the patch applied at the time I was experiencing the problems.  The DAQmx driver version was the version that was supplied on the DVD that we received for LV2009.  I believe the actual version number was something like 8.9.5.

The loop time was determined as follows:

A simple vi I was written in a while loop.  The data acquisition was conducted using the DAQ assistant sampling 1 channel on the SCXI thermocouple module in a SCXI 1000 chassis.  Inside the loop of the vi the getdatetime function was placed and wired to an indicator on the screen.  The vi was then ran.  Observation showed that the loop time was typically 3 seconds and sometimes 6 seconds by keeping track of the datetime indicator on the front panel.

The problem appears to be resolved now.  I had pulled off the LV2009 installation and put back on the 8.6 installation.  Recreated the vi and everything worked fine. As a sanity check I went ahead and reinstalled LV2009.  Recreated the vi again and everything works fine now.  The only real difference between the two installations is that I am using the latest NIDAQmx drives (I believe version 9.0.5).  It could have been just some sort of transient issue that resolved itself either by reinstallation or by rebooting.   Not sure.  I was just initially very concerned given that another posting had mentioned loop times of 3 seconds just like I was experiencing.

Thanks,

Steve