PXI-6289 giving incorrect readings

[schang8]

We have two test setups using multiple PXI-6289 modules in two separate PXI-1045 chassis.  One runs SignalExpress v.4.0.0 and the other runs Measurement & Automation Explorer v4.7.2.f0.  They use DAQmx components of versions 9.2.0 and 9.2.1 respectively.  They're hooked up to different test boards that have the same device under test.

The issue is that one channel on each board (different channels between boards) is reporting an unrealistic and incorrect value, somewhat more often when the sampling rate is very high.  Because this is happening between two different test boards and two different software interfaces, we tenatively conclude that the issue might be with the DAQ modules themselves.  Is this known behavior?

[JustinP]

Hi,

Are you sampling multiple channels on each PXI-6289?  The maximum sampling rate for this device is 500 kS/s (aggregate).  What you are experiencing might be "ghosting" where reminance of the previous acquisition are carried over to the next.  If this is the case then reducing the sampling rate should resolve this issue. 

Justin

[schang8]

When I get the test set up next, I'll try incrementally decreasing the sampling rate--I'm dealing with high-speed transients, so reducing sampling rate is a bit undesireable.  Also, if it matters, does ghosting carry over the previous reading, or is it undeterministic?  The reading I'm getting is 1.05 amps when the anticipated real value is several orders of magnitude smaller.

Thanks!

[JustinP]

Hello,

Ghosting is the previous value getting carried over.  Is the channel the same everytime for each unit? I know you said it was different between the setups but is it different for each test on the same setup?  Also, what rates are you sampling at?  This will give me a better idea of your setup.  I am attaching a link that discusses ghosting for your own knowledge and you may see something that applies directly to your application. 

http://digital.ni.com/public.nsf/allkb/73CB0FB296814E2286256FFD00028DDF

Regards,

Justin