Project Case Study · Apr 2026

Closed-Loop PID Temperature Control: IMC Tuning

A small heater that holds whatever temperature you dial in. I built the circuit, measured how the heater actually behaves, then tuned a controller to bring it to a target quickly and hold it there without much fuss. An Arduino does the thinking, reading a thermistor and adjusting heater power many times a second.

HardwareArduino, MOSFET driver, heater + thermistor

MethodReaction curve, then IMC tuning

ResultClean rise, about 2% overshoot

TimelineApr 2026

The heat block: a power resistor acting as the heater with a thermistor mounted next to it on an aluminum rail — The heat block. A 16 ohm power resistor does the heating, with a thermistor reading its temperature right next to it.

The idea

The goal is easy to say and surprisingly fiddly to get right: keep a heater at a set temperature. You pick a target with a knob, and the controller decides how hard to drive the heater so the measured temperature lands on that target and stays there. The Arduino reads the temperature from a thermistor, compares it to your target, and sets heater power through a small MOSFET driver board that switches the supply on and off quickly to control the average power.

Getting to know the heater

Before tuning anything, I needed to see how the heater actually responds. With the block sitting under a plastic bin to keep drafts off the sensor, I bumped the power up by about 20% and recorded the temperature climbing until it leveled off. That gives the S-shaped curve below. Reading it tells me three useful things: how much the temperature moves for a given amount of power, how long it waits before reacting, and how slow it is overall.

Reaction curve showing temperature rising in an S-shape after a step in heater power, annotated with dead time, time constant, and total change measurements — The reaction curve. A step in heater power gives an S-shaped rise, and the marked-up lines pull out the delay, the speed, and the total change.

Why a method beats guessing

To show why the measuring matters, I first tried plain proportional control. With a gentle setting the temperature got close but always parked a few percent short of the target. With an aggressive setting it shot past and oscillated for a long time before settling. Neither is good, and that is exactly the gap a proper tuning method fills.

Tuning it properly

Using the numbers from the reaction curve, I calculated a starting point with the IMC method, which is basically a recipe that turns those measurements straight into controller settings. Then I tested and adjusted one value at a time. The first attempt sagged on the way up, the next overshot, and splitting the difference landed it. The final response rises cleanly to the target with only about a 2% overshoot, then holds steady, with the heater easing back to just enough power to keep the temperature there.

Final tuned response chart showing the measured temperature stepping up to the setpoint with a small overshoot and settling, while the control output eases back to a steady value — The final tuned response. Temperature (orange) steps up to the target (blue) with a small overshoot and settles; heater power (grey) eases back to a steady hold.

What this shows

The whole point was to do it the way it is done on real equipment: measure the process first, work out a sensible starting point, then refine by watching how it actually behaves. It is a small heater on a bench, but the workflow is the same one used to tune loops in a plant.