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AD7195 - using it with a PT100?

Question asked by dirk.bruere on Jun 1, 2015
Latest reply on Dec 4, 2015 by dirk.bruere

At present I am trying to use this with a PT100. In order to limit current to about 1mA I have the AC excitation feedinging into the PT100 in series with a precision 5K resistor. I take the Reference voltage from across the 5K, and the AIN from across the PT100 sense wires.

 

Is this correct, or should the Reference be direct from the Excitation voltage?

Additionally, how do I actually convert to a precision temperature? I can get an approximation by assuming a 5V signal, but how do I employ a ratiometric approach which does not imply an infinite precision 5V power supply? And how do the Offset and Fullscale registers figure into this? Resolution is milliKelvin, but accuracy is Kelvins which is rubbish

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