Hi all,
Our customer has decided switch form a thermistor temperature sensor to a 500-ohm RTD in an aircraft environmental control system. They will not run new wiring, so we are stuck with a 2-wire solution rather than the preferred 4-wire.
I found a TI guide for a 4-wire implementation, which has helped me select appropriate op amps and the current source, but I would like help customizing the circuit to our 2-wire implementation. I assume there isn't much point in using a differential amplifier if one end of it is just connected straight to ground (unless that will help cancel out onboard noise?). Here is the 4-wire guide: http://www.ti.com/lit/wp/snoa838/snoa838.pdf
Some details on our system:
-The sensor is connected with 52-feet total (26ft each side) of 22AWG wire.
-They have selected a 500 Ohm RTD, designed to be driven at 0.5mA.
-Our system voltage is 3.3V.
-They require +/- 3degF accuracy over the temperature range from 30-185F.
-I found a resistance table that says for a 500 ohm RTD that is 496-664 ohms.
-I think we'll need to use an op amp to gain up the signal by 7-10x to make the most of our 12-bit ADC.
Any help would be appreciated.
Thanks