Answer
Jul 13, 2024 - 12:44 PM
On/off control toggles a controller's output fully on or off at a setpoint value. In a heating operation, the heater would be turned fully on below the setpoint and fully off above the setpoint (the reverse would occur in a cooling operation). PID (Proportional-Integral-Derivative) control continuously adjusts output depending on the process temperature in relation to the setpoint. For example, in a heating application with a relay output connected to a heater, the relay will cycle the heater power on and off. When far below the setpoint, the heater will be turned fully on, but as the temperature of the process approaches the setpoint, the controller will cycle the power to the heater with the duration that the heater is on decreasing as the temperature approaches the setpoint. PID results in smoother and more accurate control.
