Pt100 fluctuating readings | LabJack

Pt100 fluctuating readings

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comm's picture
Pt100 fluctuating readings


I'm using a U3-HV with LJTick-Resistnce to read 2 Pt100 as the attached scheme.

I use the formula:

R=(2.5-Vin)/Vin * 1000    ; to get Pt100 resistance

T=(R-100)/0.385  ; to get  Temp. in °C

My problem is that Temperature fluctuates between 24 and 37°C. It seems to much for me.

What did I do wrong?


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LabJack Support
labjack support's picture
So how much voltage

So how much voltage fluctation are you seeing?  We expect a count (~600uV) or so on low voltage analog inputs (FIO/EIO).  Look at the "Resolution" section here:

The T4 is very similar to the U3-HV and you can see the math in this section results in a resolution of about 0.55 degC per count.