Glossary · Sensors and measurement
Hysteresis
Also known as: Switching hysteresis
German: Hysterese
In measurement and control, hysteresis is the difference in the output of a sensor or switching device for the same input value, depending on whether the input is rising or falling. In switches, it is often deliberately designed in to prevent chattering.
- Sensors
In one sentence
Hysteresis is the difference in output for the same input depending on whether the input rises or falls, wanted in switches, unwanted in sensors.
Example
A level switch turns a pump on at 80 % and off at 20 %; the 60 % hysteresis prevents the pump from starting and stopping continuously.
How it applies
- Engineering: In a measuring device, hysteresis is an error component and appears in datasheets together with Linearity and Repeatability. In switching functions and alarms, a defined hysteresis or deadband is designed in so that small fluctuations around a threshold do not cause repeated switching.
- Commissioning: Too little hysteresis causes chattering outputs, contact wear and alarm floods; too much delays reactions. Set it according to the process dynamics.
- Operation: Alarm deadbands are a form of hysteresis. They help reduce repeated alarms without hiding real conditions.
- Documentation: State both switching points or the threshold plus the hysteresis. A single value such as switch at 5 bar leaves open when the output resets.
Hysteresis vs. repeatability
Hysteresis is a systematic difference between rising and falling input. Repeatability describes random scatter under the same conditions.