In control systems, what does the term "hysteresis" describe?

Hysteresis in control systems refers to the phenomenon where the output of a system does not immediately follow changes in the input, resulting in a delay or lag in the system's response. This characteristic is often related to systems that have a memory effect; the output depends not just on the current input but also on the history of past inputs.

In practical applications, hysteresis might be observed in systems such as thermostats or pressure controllers, where the output must exceed a certain threshold before changing states. For example, a thermostat might need to heat a room to a specific temperature before turning the heating element off, even if the room temperature rises above that level. This ensures stability and prevents rapid oscillations around the setpoint, allowing for smoother operation.

This understanding of hysteresis is essential for those working in control systems, as it impacts design considerations and the selection of control algorithms that should be applied.