I'm trying to build a basic circuit that can monitor a thermocouple, compare the resistance to a known source and then adjust a valve to maintain a certain temperature.
I have designed and tested the circuit to compare the thermocouple with the known voltage and have an output of between -5 and +5v. Ideally I'd like to take that variable voltage and simply add it to the voltage currently going to the valve so the final voltage will either go down, stay the same or go up.
Is there a way I can use an op amp to monitor the final voltage and the sum it to the variable one? I've attempted to use a capacitor as a 'memory' for the final voltage, but I'm not getting anywhere.
As a side note, I'm running at 24V with a virtual ground to create +-12V. The thermocouple and known source are both variable resistors with their outputs going through a differential amplifer to give the -5V to +5V range. The valve takes a 0-20ma signal which I'm generating from 0-5V.