On-Off, Proportional & PID Control

The controller in a feedback loop has to decide, given an error, how hard to push the actuator. The rule it uses is the control mode, and the choice runs from the crude on-off switch in a domestic thermostat to the smooth PID algorithm running most commercial plant. The mode determines how tightly the loop holds its setpoint, and therefore how much energy it wastes in overshoot. This lesson walks the three modes in order of sophistication and the energy each costs.