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I am examining the st-micro rtd circuit for the STM32373C-EVAL kit. What does this circuit do?

Can I use it to support both pt100 and pt1000 rtd elements? The circled area is the point of confusion.

op-amp-circuit

http://imgur.com/QsWV0hI

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This circuit is a precision constant current source for the PT100 (R30 in the schematic). This is a Howland current source (principles of operation here).

If you use as is it with PT1000, it would work in general. You might see more self-heating. The output would rail at a lower temperature.

The current is inverse-proportional to R3x**. You can reduce the current by increasing R3x.

** The designator is obscured by the black circle. The resistor is directly above JP18.

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