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Warning 200011 occurred at DAQmx Start Task.vi:7220001, Clock rate specified is so high that it violates the settling time requirements for the acquisition

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Hello all,

 

I have two 32 channel TC 2095 terminals which are connected to two SCXI 1102 B modules, which are connected to a PXI-6251 card within a PXI-SCXI-1050 chassis. I then use a PXI-8360 module and PCIe 8361 card to connect to my PC. I'm running Labview 2015 and have DAQmx 15.

 

When I try and acquire all 64 thermocouple above 650 Hz per channel, I get the warning message:

 

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Warning 200011 occurred at DAQmx Start Task.vi:7220001


Possible reason(s):

Clock rate specified is so high that it violates the settling time requirements for the acquisition.

Reduce the clock rate, or the accuracy of the measurement might be compromised.

---------------------

 

When I reduce the number of channels sampled or the sample rate, the error is no longer thrown.

 

I am trying to find where the bottle-neck is occuring in the system which causes the error message. At 650 Hz, 64 channels, the total sample rate is 42 kS/s (21 kS/s per SCXI-1102B module), which as far as I can tell is below the maximum sample rate of the SCXI 1102B (~ 50 kS/s for maximum 16 bit accuracy according to another thread), the PXI-6251 (1 MS/s aggregate for multiple channels), and the PXI-8360 (132 MBytes/s).

 

One other strange thing is that I have tried another M-series card - replacing the PXI-6251 with a nominally slower PXI-6221 (250 kS/s aggregate), but the maximum sample rate is still 650 Hz, which suggests to me that it isn't the M-series card but something else.

 

I am confused-  any ideas where the bottleneck is occuring?

 

Many thanks,
Ben

 

 

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Accepted by kirollosb

Dear Ben

 

I had a thourough look into the warning message you describe and you are totally correct about the timing considerations you made.

 

It seems that the warning is generated by the SCXI 1102B device, which is able to switch within 3us (333kHz), but needs more time to settle to the least significant digit. The DAQmx driver doesn't know this settling time, so it gives a warning 200011 if the sampling is faster than the switching time plus 20us settling time as a safety margin (so in total 23us).

It seems that you are reading all 64 channels seriell, thus you will get a warning if you sample faster than 1/(23us*64 channels) = 679Hz.

 

The actual settling time to the maximal precision of the 1102B (which can be found in the specifiations) is 10us so you can safely negate the warning if you stay below 1/(10us*64 channels) = 1562Hz.

 

I hope I could help you to understand where the bottleneck is occuring and let me know if you need further information.

 

Andreas Jost

Applications Engineer

National Instruments

Andreas
CLA, CTA
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