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Read thermocouple in mV

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1. I have a 9213 TC card with cDAQ chassis. If I read AI Voltage in DAQmx, will it give me mV readouts? If I apply a custom scale (linear, slope = 1, Y-intercep = 0) to an AI Temp TC (DAQmx Create Virtual Channel VI), will I accomplish the same thing?

2. In the 9213 manual, it states a sampling rate of 75 S/s All channels (including autozero and CJC channels). If I'm using all 16 channels, does it mean I get 16 X 75 = 1200 readouts every second at maximum sampling rate? The word "All channels" is unclear to me.

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No, the 9213 is a multiplexed device meaning that all TC use the same ADC circuit and must share it.  That means it's 75S/sec aggregate.  The sample speed = Max Sample Rate / # of channels used.

 

EDIT:  BTW, sure you can read a TC in mV and scale it however you want.  The DAQ Temperature VIs are just a convenient way to use standard TC types, CJCs, etc.

LabVIEW 8.5.1 - 2019 Pro Dev
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Checkout the product page here: http://sine.ni.com/nips/cds/view/p/lang/en/nid/207150 thought, it says High-speed mode for up to 1,200 S/s (aggregate). I am just confused by the manual saying 75S/s all channels, and this product page.

 


NIquist wrote:

No, the 9213 is a multiplexed device meaning that all TC use the same ADC circuit and must share it.  That means it's 75S/sec aggregate.  The sample speed = Max Sample Rate / # of channels used.

 

EDIT:  BTW, sure you can read a TC in mV and scale it however you want.  The DAQ Temperature VIs are just a convenient way to use standard TC types, CJCs, etc.


 

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Yes, it seems this model has high speed OR high accuract modes.  It appears to have a 100 S/s limit though according to the specs.  [ From Manual:  The maximum sample rate = 1/(Conversion Time × Number of Channels), or 100 S/s, whichever is smaller. Sampling faster than the maximum sample rate may result in the degradation of accuracy.

 

I couldn't find anything that explained if you give up bit resolution in the high speed mode but your measurement stability / noise level will suffer.  There is a give a take but I believe expecting to use any speeds over 100 S/s aggregate will be problematic.  It would be rare to need that speed for monitoring temerature changes though assuming your part has any mass.

LabVIEW 8.5.1 - 2019 Pro Dev
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I believe you are mixing up bandwidth from sample rate. They are not the same thing. The bandwidth determines how well your sample will be able to match the actual temperature curve. If you exceed the bandwidth, the curve will be distorted.

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How does 9213 handles autozero and internal CJC if you use a voltage task instead of TC one in DAQmx?

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Accepted by topic author pellet8

It doesn't.  If you choose to read a TC as a raw voltage you have to take care of the details yourself. 

LabVIEW 8.5.1 - 2019 Pro Dev
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