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Precision pt100/RTD circuit?

Question asked by awallin on Jun 10, 2013
Latest reply on Jun 26, 2013 by ChrisD.Rama

Hi all,

I'm wondering if someone has a precision temperature measurement front-end circuit they would like to share?

From googling/reading it seems there are a few considerations:

- 4-wire measurement to avoid lead-resistance effects

- ratiometric operation of the ADC to reduce effect of current-fluctuations in the RTD

- AC-excitation to eliminate offset-effects, thermovoltages, etc.


My application has very long time-constants, so the 4.7Hz (or lower) conversion rate of e.g. the AD7195 is sufficient. Maybe there are other converters I should look at?


Also, I am wondering about the role of voltage-reference stability for this application (given that the measurement is ratiometric, and AC-excited). A colleague has worked with the LTZ1000 ultra-precision reference, but I have a feeling it might not be worth the cost&effort and an ADR421 or similar could be used instead (i.e. gain/offset errors are dominated by other parts, not the voltage reference).