Bang–bang control

A two-position controller is a discontinuous working controller with two output states. Depending on whether the actual value is above or below the setpoint, the upper or lower output state is entered. Two-point controllers are then used when the control variable is not continuous variable, but can only switch between two states, such as On / Off. Although the two-point controller reaches the steady state, but never comes to rest. But with strong changes in the setpoint can compensate deviations faster than is possible with other control methods.

The best-known example of a two-point controller is the thermostat that controls a heating or cooling device with non-variable performance. In contrast, a heating thermostat valve which controls the flow to radiators for space heating, a proportional controller.

To avoid rapid oscillations of the output, two-position controller often have a built-in hysteresis, that is, a certain dead band around the threshold, by which the actual value must change to cause a switch to the opposite output state. For example, on a thermostat heater upon reaching 21 ° C., but only when it falls below 18 ° C again, which corresponds to a hysteresis of 3 ° C.

Both the slider itself and the hysteresis may be mechanically (e.g., bimetallic ) or be realized electronically.

A closer examination of the two-point controller, there are articles in the controller.