# What is the hysteresis effect

## Hysteresis

### Which does ______________ mean Hysteresis?

#### according to Duden What is a hysteresis?

the hysteresis [gr.]: The fact that an effect falls short of the current level of the variable force that determines it.
Technical term physics: Delayed change in effect after changing the cause.

#### Clear explanation of hysteresis in the temperature controller

A temperature controller switches the heating on when it is too cold and off when it is warm enough. So it switches on and off depending on the temperature. The temperature at which switching is to take place is the set target temperature (e.g. 26.0 ° C). If the switch-on and switch-off temperature were the same (e.g. below 26.0 ° C on; above 26.0 ° C off), the controller would not know whether to switch on or off when it measured exactly the set temperature. In practice it would switch on / off quickly, which would not be healthy for the relays or the connected pump, valve, etc.

Each controller therefore needs a different switch-on and switch-off temperature. The difference between the switch-on / switch-off temperature is known as the hysteresis.

#### Example of a temperature controller

The target temperature is set to 26.0 ° C. The hysteresis is 2.0 ° C: This temperature controller would switch the heating on if it measures below 25.0 ° C and only switch it off again when the temperature rises above 27.0 ° C.

Analogous to the example for a two-point temperature controller, there is also a hysteresis for level sensors, etc.

#### Ideal hysteresis how big should it be?

Small hysteresis: The advantage is precise regulation. Disadvantage of switching it on / off too often.

Big hysteresis:
The advantage is seldom switching on / off. The disadvantage is an imprecise regulation.

Ideal hysteresis: Our controllers therefore have the ideal hysteresis of approx. 1.6 ° C. With some controllers (e.g. ALLPOOL, PSM04, PSM03, DPOOL, DIGISOL, DIGIFAT) you can even set the hysteresis yourself.

#### Prevent relay chatter with hysteresis

If the temperature sensor lines are laid incorrectly, 50 Hz mains voltage can be induced in neighboring lines and cause the relay to rattle. This rattling overwhelms the relay even with very low switching capacities. This problem can be alleviated a little by increasing the hysteresis.