U3-HV shows ~20mV lower voltage through python than actual voltage | LabJack
 

U3-HV shows ~20mV lower voltage through python than actual voltage

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MT
MT's picture
U3-HV shows ~20mV lower voltage through python than actual voltage

Hello LJ,

I began using U3-HV and seeing a problem in voltage read --- looks like a bit lower than actual voltage.

Using python script (setting FIO4 as analog and use getAIN to get the voltage of 0.8V - 2.4V), the voltage I get from LJ is always lower than actual voltage.

I compared the voltage I got from LJ with other several equipments, so I'm sure LJ gives me lower voltage. Interestingly, when I used LJ GUI(LJControlPanel), I see the right voltage (ex. ~1.38V), but I get ~1.36V using python script.

Hope I can get some advices.

LabJack Support
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After opening the U3 and

After opening the U3 and before the first analog input reading, make sure to get the calibration constants from the device and for your U3 object. This will ensure that the voltage from getAIN is the calibrated voltage like in LJControlPanel. Otherwise voltage conversions will use nominal calibrations which is probably what you are seeing. The first part of the Basic I/O section of the Low-Level Commands Quickstart mentions getCalibration usage:

https://labjack.com/support/software/examples/ud/labjackpython/low-level

MT
MT's picture
Do you mean just adding "d

Do you mean just adding "d.getCalibrationData()" is good enough?

LabJack Support
labjack support's picture
Yes. See if that helps with

Yes. See if that helps with getting the Python readings closer to the LJControlPanel ones.

MT
MT's picture
Yeah, that gives me a better

Yeah, that gives me a better result.

Thx.