# Circuit Design for Temperature Sensing PID Controller using Op-Amps

Basically, the idea is that I'll have a temperature sensor (LM35) that will sense the temperature of a certain metal can. This metal can is subjected to heat by a gas burner, and the gas burner's output would be reduced or turned off if the metal object is at a temperature of 110 deg C, and would be increased or turned on if it falls below 100 deg C. I'm thinking of using a servomotor connected to an Arduino, connected to the PID controller, to mechanically turn off or on the valve when the can is hot or cool enough.

I'm thinking of following this circuit for the PID Controller

For Verr, I will be using a comparator circuit that is connected to a constant V source of 3V, and for the temperature sensor, I will be connecting it to a non-inverting amplifier. What gains, resistor values and additional components should I use to make it work properly?

I am also welcome for suggestions of different circuit designs,as long as it uses op-amp based PID controllers.

• Most slow-action PID loops use just the integral part. For motor control some derivative feedback is used to start/stop motor or a change in load. Proportional is seldom used as it has no time delay, so racing and erratic behavior can be the result. – Sparky256 Feb 5 '18 at 4:44
• But what if I want the servomotor to move in an instantaneous motion? Like if the temperature sensed is 110 deg C, the motor will rotate 180 degrees clockwise, and ccw if temp. falls below 100. – RenV Feb 5 '18 at 6:20
• Then you need to judge how fast 'instantaneous' is, and adjust the derivative time-constant and level so it does not slam the motor, just a short term boost in speed. That is all the derivative is meant to do. – Sparky256 Feb 5 '18 at 6:29
• Don't use a comparator to find the error signal. It will introduce so much gain the loop will become unstable. Use a unity gain differential amplifier opamp circuit instead. – Sven B Feb 5 '18 at 6:47
• Three opamps should be fine, and you can combine P and I in just one of them. You need a difference amp (error), the PI amp, and then the inverter with or without gain (probably.) What makes you think you need the D term in this circumstance? – jonk Feb 5 '18 at 10:17