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Basic Electronics » PT100 temperature sensor reading

June 17, 2012
by RogerFL
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I'm researching how to design a simple-ish circuit to read a PT100 temp sensor with 3 wires.

I've read that sophisticated circuits (balanced wheatstone) can get accuracies as low as 0.1 C. I'd be happy with 0.5 C error and don't want to try to use a digital potentiometer (sp?) to get the "balanced" wheatstone circuit that seems to be the most popular approach. Also some circuits seem to require a constant current circuit involving multiple opamps.

I'm hoping I can get good enough results just using the 5v output of the 7805 as the source voltage and measuring the voltage in the "unbalanced" wheatstone circuit.

Here's an interesting calculator that includes the equations I'd use:


Here's the circuit I'm proposing, on

pt100 reader circuit on circuitlab

Would love to get advice and feedback on this strategy.

This is for my seemingly lifelong project of smoker/grill controller so it needs to sense higher temps in the 25 - 500 C range.


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