I tried to find out the formula for finding the value Vout as a function of the input voltage. I've used the KCL (I think it's Kirshoff-current-law) at the various junction points. I got a formula that gives values that are offsetted by 0.2Volts from the output produce by a simulation of the circuit in Proteus (original diagram in LTSpice as seen in the picture above). My question is: is it common for proteus to add an offset during the simulation, or am I necessarily making an error in my computations. Thanks in advance
I've found a pretty acceptable solution. The formula for the output voltage of the diagram above is provided in another question, I've recently posted: Output Voltage Formula verification of Operational Amplifier circuit. The diagram can easily be simulated in Proteus and provide a temperature range between 0 and 400 degree celcius. Where Rx=R6=Resistance of the PT100 sensor.
The problem I was having was that I was wrongly connecting my PT100 (3-wires) RTD within the circuit (the above circuit assumes a 2-wire RTD). The other mistake was to use a 5V supply source for the Op-Amp: no, the voltage source for the op-amp needs to be at least 6V. Preferably, the op-amp should be powered by a 6V and -6V as I still get wrong results with temperatures below 50 degree Celsius. In my case, I'm mostly concerned with temperatures above 100 degree Celcius. So I'm fine with only a 6V supply for the Op-Amp.