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Reading 8 RTDs faster than 1 Hz using NI 9216

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I want to read 8 channels from a NI 9216 installed in a cDAQ 9189 faster than 1 Hz, but straightforward code is taking 200 milliseconds/channel.  I set up the task to read 8 channels, set the sample mode to continuous, and loop on reading NChan 1 samp.  The loop happens in 3 msec, but the data only updates every 1.6 seconds.  What am I doing wrong?

 

This VI reads 1 to 8 channels of RTD data using an NI 9216 module in a cDA!9189 chassis read over an ethernet cable by a Dell computer running Windows 7 Professional.
I am surprised by two things. First, the acquisition loop seems to operate too quickly, and takes just 3 msec to execute. Since I'm asking the module to read 8 channels of data, and its specs are 400S/s Aggregate, I expected a 20 msec acquisition time by the DAQms Read function.
Second, the actual data read updates much too slowly. The Change Time indicator reads 0.2 sec when reading 1 channel, and 1.6 seconds when reading 8 channels.
I don't think it's relevant, but you can see from the data that I have one RTD connected. The other 7 are disconnected.

 

I am using LabVIEW 2019 and NI DAQmx Device Driver 19.0.

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According to the specs for a 9216, high resolution mode takes 200 msec/channel.  So it is exactly the results you are getting here.

 

High speed mode is faster, but I haven't found how you set the module to be in high speed vs. high resolution mode.

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Accepted by topic author PghFool

I haven't verified it myself, but maybe this link will help: https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000YHjCCAW&l=en-NZ 

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Perfect!  Setting that setting to High Speed gives a 20 msec loop time, just as I had hoped.

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While I am glad you found a "Solution," I have to ask you to THINK about this for a moment.......

 

Why?  Seriously, monitoring an RTD output at high speeds is very seldom the correct way to make a proper measurement.  I assume that you are attempting to do this in the same universe as these Forums reside.  Here, Temperature just doesn't change that fast except in highly unusual conditions.   It involves moving considerable energy into or out of the RTD and the mass it is thermally coupled with!  Anything with such a small "theta jc" (a coefficient of thermal transfer rate) would be either changing much slower than the resolution or the RTD in hi-speed, low-res mode or completely swamped by the self-heating of the measurement system. 

 

So, I urge you to go back to the drawing board and review your measurement needs in light of the real world physics involved.  

 

Of especial note, NI does not have support for hardware in alternate or parallel universes where Newton's Laws are not enforced. 


"Should be" isn't "Is" -Jay
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