How is "hysteresis" defined in control systems?

Hysteresis in control systems refers to the phenomenon where there is a lagging or a delayed response in a system's output when it reacts to changes in input. This behavior occurs because the output does not follow the input changes instantaneously, but instead, it depends on the current state of the system, which can include previous inputs.

In practical terms, this means that for a given input change, the resulting output will vary based on whether the system is increasing or decreasing in terms of input. This can lead to a differential response in the output that is different for a rise in input versus a fall in input, creating a loop or a band within which the system operates. Hysteresis is a critical concept in systems such as thermostats or in magnetic systems, where the output may take different paths depending on the history of inputs due to this lagging effect.

Understanding hysteresis helps technicians design and troubleshoot control systems, ensuring they can identify when a system may exhibit this effect and account for it in their analysis and operations.