AI settling time warning code

[mikehoffa]

I am using an older 6024E DAQ card with an SCXI chassis and AI, TC, DI, & DO modules.  I want to run it between 5kS/s and 10kS/s on 12 AI channels in a continuous acquisition mode.  The DAQ card specifies a 5us settling time.  For 16 AI channels that would be a rate of approx. 12.5kS/s so it would seem that I should be able to run the conditions I'm after.  However, if I set a rate of 3kS/s the system configures and runs ok (no errors or warnings and it acquires data) but if I set a rate of 4kS/s or higher the DAQmxStartTask() function returns warning code 20011 which is a warning about exceeding the DAQ settling time and therefore a loss in accuracy of the data.  How is the settling time computed for this warning code?

[Brian_P]

Mikehoffa,

Thank you for using the National Instruments forums.  I am sorry that you are receiving this error.  The 6024E has a maximum sampling rate of 200 kS/s so with 12 channels at 10 kS/s so you are correct you aren't coming close to maximum sampling rate.  I think that the problem lies in the SCXI chassis or the modules within the chassis.  From looking at this knowledgebase article your I believe that is where your bottleneck is.  

So with that being said, what SCXI chassis are you using, and which modules are you using with your chassis?  Also how many channels are on each module?  One last question, would it be possible for you to post a screenshot of the error so I can see exactly what is error text is?   I am not finding much on error code 20011 so I might be more successful using the error text.

Regards,

Brian P. 

[mikehoffa]

Hi Brian,

Thanks for the reply. The SCXI chassis I'm using is an SCXI-1000. The 4 modules are (1) an 1102C for general AI channels configured for +/-10V, (2) an 1102C setup for TC channels, (3) an 1162HV DI, and (4) an 1161 DO. One AI task is configured to continuously acquire 8 channels of general purpose AI from module 1 and 4 TC channels from module 2.  The DI and DO are read from and written to on demand at about a 10 Hz rate with the DO actually changing states at 5 second up to hour-long periods. The DAQmxStartTask() function returns negative values for errors, 0 for everything OK, and positive values for warnings. The problem you are having with searching for 20011 is that I gave you the wrong code.  It is actually 200011 (3 zeroes). Using the returned code and sending it to DAQmxGetErrorString and placing the returned string in a popup message yields the following text:

"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."

The 1102C is rated for 333 kS/s max sampling rate and has an "input signal bandwidth" spec of 10kHz.  There's a "Step response (10 V step)" spec which lists 200us and 1ms for +/-0.01% and +/-0.01% accuracy (which I assume is a typo else I can't figure out what it means).  But none of these specs seem to match with the 3kHz OK and 4kHz warning generation I'm experiencing.

I can figure out how to deal with the warning - ignore it, ask the user what to do, reduce clock rate to avoid it, etc. - but I'd like to be able to predict what DAQmx will do without trial and error probing.  So my real problem is that I don't understand how it calculates the settling time requirement or whatever is generating this warning code.

Thanks for your time and efforts.

[Brian_P]

Mikehoffa,

Thank you for getting back to me.  With the new error code I was able to find a knowledgebase article that explains how this works.  However from doing a little more research I did find that this error should have been fixed with DAQmx 8.7.   I would suggest upgrading your DAQmx driver to 9.3.  This driver will work with LabWindows 8.1 and above and is also compatible with your card.

I hope that helps,

Brian P.