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I'm looking at performing accurate temperature measurements with a three wire RTD, and I'd like to be able to measure the resistance and thus the temperature using an arduino. The accuracy I'm looking for is better than 0.1Ω @ 100Ω.

I was told that to get good accuracy, I would first need a stable accurate low current source and very accurate low temperature coefficient resistors in a wheatstone bridge.

I was wondering if there was to better utilize the arduino's capabilities to perform this measurement, or is the external current source + wheatstone bridge the way to go?

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  • \$\begingroup\$ With the many analog inputs you can easily make it somewhat autoranging. You only have a 10 bit DAC (1024 steps) so you need to figure out something smart to reach .1% resolution. \$\endgroup\$ – jippie Sep 6 '13 at 20:57
  • \$\begingroup\$ @jippie -The range is quite small, between 100 and 150 ohms. \$\endgroup\$ – nbubis Sep 6 '13 at 20:58
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    \$\begingroup\$ @nubis: Have a look at LMP90080 series from TI, for an integrated solution for 3-Wire or 4-Wire RTD. \$\endgroup\$ – AKR Sep 7 '13 at 3:57
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    \$\begingroup\$ @AKR +1. AD7793 (and family) are in the same class as LMP90080. \$\endgroup\$ – Nick Alexeev Sep 7 '13 at 17:51
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Source: application note AN687 by microchip. It shows one of the methods of signal conditioning for 3-wire RTD. Notice that this method doesn't require a Wheatstone bridge.

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  • \$\begingroup\$ Nice :) does the final accuracy strongly depend on accurate resistor values? also, I guess one would have to get a stable voltage from the arduino \$\endgroup\$ – nbubis Sep 6 '13 at 22:17

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