Pt100 temp sensor and ad7730

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baby_1

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Hello
Im starting to work with PT100 temp sensor.i series a 100ohm resistor to it and wants to find the voltage across from the 100ohm resistor that should change with temp.but as i tested it by PIC18f4550 ADC (10bit adc) it doesn't work properly (doesn't change voltage) and the output of adc was fixed to (471-467) i wonder why it doesn't work while when i tested the PT100 with ohm meter and find that it resistor change via each centigrade (.4 ohm resistor increase when 1centigrade temp increase)

now i want to use ad7730 to sensing the PT100 , what is best circuit via PT100 and AD7730?

Thanks
 

I don't know why you say it didn't work, a PT100 is essentially a resistor, so as long as you can measure a voltage, then it must work. Anyway..
Check the AD7715 datasheet, and apply the similar design to your ADC, if the datasheet doesn't already have a PT100 example.
In summary, use a constant current source, and use it dual-purpose - to generate your reference voltage to the ADC (using a resistor), as well as
to develop a voltage across the PT100. Something like 400uA as in the datasheet, because you don't want your PT100 to become self-toasty.
 

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