====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.

===Example===

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.

==Without Hysteresis==

^Input Value^Output Value^
|29.9|Off|
|30|Off|
|30.1|On|
|30.2|On|
|29.9|Off|
|29.7|Off|
|30.1|On|
|29.9|Off|
|25|Off|
|23|Off|

==With Hysteresis==

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

^Input Value^Output Value^
|29.9|Off|
|30|Off|
|30.1|On|
|30.2|On|
|29.9|On|
|29.7|On|
|30.1|On|
|29.9|On|
|25|Off|
|23|Off|