Comparison

PID vs On-Off Control: When Is Each Appropriate?

On-off control switches fully around a setpoint. PID adjusts smoothly. Compare process response, variation, actuator cycling and tuning.

Controls & Instrumentation · Last reviewed October 17, 2026

Short answer: on-off control is enough when the process is slow, a band of variation is acceptable and the actuator can switch often, such as a room thermostat. PID is the better choice when the process must hold close to a setpoint, the actuator is modulating, or frequent switching would wear the equipment.

	On-off (with hysteresis)	PID
Output	Fully on or fully off	Continuous, from 0 to 100%
Variation around the setpoint	A band, set by the hysteresis and the process speed. The process always cycles	Can hold very close to the setpoint when tuned
Actuator	A relay, contactor or on-off valve. Cycling wears it	A modulating valve, a drive or a proportional output, or a time-proportioned relay
Tuning	One setting: the differential (hysteresis)	Three settings (gain, integral time, derivative time) that need tuning
Process types	Slow processes with large thermal mass, tolerant of swings	Faster or tighter processes, such as flow, pressure and precise temperature
Disturbances	Responds after the band is crossed	Corrects continuously, with integral action removing steady offset
Implementation effort	Minimal	More: instrument range, tuning, anti-windup, testing
Typical uses	Thermostats, pump start-stop on tank level, compressor pressure switches	Process temperature, flow loops, pressure control, speed control

A cycling example

A heater controlled on-off with a 2 °C hysteresis on a slow tank might switch on and off every few minutes. If the process is slow and the tank tolerates ±1 °C, this is fine and wears a relay lightly. If the heater is a contactor driving a large element and switches every 30 seconds, the contactor wears out sooner than the process justifies. A PID loop with a time-proportioned output, or a modulating drive, switches less abruptly and holds the temperature tighter.

How to choose

State how close to the setpoint the process must stay, and how much variation is acceptable.
Look at the actuator: can it switch often, or does it need smooth modulation?
Estimate the speed of the process and the dead time. Very slow processes tolerate on-off.
Consider who will tune and maintain it. A poorly tuned PID loop can be worse than on-off.
Start with the simplest scheme that meets the requirement.

Common mistakes

Using PID with an actuator that can only switch on or off, without a time-proportioned output.
Setting the on-off hysteresis too small, which makes the output chatter.
Using full PID where on-off would have been adequate, and spending time on tuning.
Skipping anti-windup and output limits on a PID loop with a saturating actuator.

Related tools and labs

Calculators, labs and simulators are part of the All-Access Pass.

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Questions

Is PI enough?

For many loops, yes. The derivative term is often not needed, and it amplifies measurement noise.

What does hysteresis do?

It sets a gap between the switch-on and switch-off points. A wider gap reduces switching and widens the variation.

Educational material. Examples use simplified, hypothetical inputs and are not a design, a construction document or professional engineering advice. Confirm requirements with the codes and standards adopted where the work is built and with a licensed engineer.

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