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U3-HV AIN Range and Resolution in LabVIEW

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#1 4Strings

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Posted 19 August 2014 - 10:15 PM


I am building a system using both a UE9-Pro and a U3-HV using LabVIEW, and am wondering what values are need for Range and Resolution in the eAIN Block Diagram module.

I've built many systems using UE9s and have found that setting the Range to 3 and the Resolution to 24 yields the best results as far as noise is concerned. I have also found that on U6s, a Range of 2 and Resolution of 12 works best.


I am testing the AINs using an EI-1034 temperature probe and seeing if there is any noise in the voltage reading. Cycling through different Range and Resolution settings has so far resulted in plenty of noise at even the second decimal point in the voltage reading.


My question is what Range and Resolution settings work best for the AIN ports on a U3-HV.




#2 LabJack Support

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Posted 20 August 2014 - 12:00 PM

The Range parameter has no effect on a U3.  There is a special range, but you get that by doing a differential read with negative channel set to 32:




The Resolution parameter is almost always left at the default of 0 on a U3, but if you pass a nonzero value you are enabling Quicksample, which is mentioned towards the end of Section 2.6.



The U6 and UE9 do use the Range and Resolution parameters in the expected manner.  The effect on noise & resolution is shown in Appendix B.  The effect on speed is shown in Section 3.1 or 3.2:









For range, you are passing the numeric constants from the header file LabJackUD.h.  The recommend technique would be to use the string constants you can see in Section 4, and use the StringToConstant function to convert these to numbers if needed.  That way you can see the readable name in your code:







General app note about noise and resolution:




Expected noise level for the U3 is +/-1 count with QuickSample off:




A count is 2.4/2^12 = 600 uV on the normal 0-2.4V range of a low-voltage analog input (FIO/EIO) and 20/2^12 = 5 mV on the +/-10V range of a high-voltage analog input (AIN0-AIN3).  FIO/EIO is usually best for an EI-1034.

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