Hysteresis

In control systems, hysteresis is used to prevent digital signals (such as alarms, alerts and relays) from rapidly flicking between their on/off or true/false states.

In these cases, you'll usually have a switch point and a certain amount of hysteresis.

The output will change when you reach the switch point. But instead of changing back the moment the value drops below the switch point, it will allow a small amount of additional dropping before it goes back to its original state. The difference between the switch point and the point that the output resets is the hysteresis.

For example, let's look at a temperature control alert, where you're trying to keep the temperature under 30 degrees.

If using a simple 'greater than' comparison, a value might reach exactly 30 degrees. But thanks to subtle variations in measurement, it will drift both above and below that value.

This time we'll look at the same input data, but we'll add 1 degree of hysteresis