Hysteresis is the difference between the point at which something is switched on and the point at which it is switched off (or vice versa). Hysteresis prevents outputs from switching rapidly on-off-on-off as the control signal hovers around the switching point.

 

Example

If an output drive was set to turn on at 50% injector duty cycle with a 2% hysteresis, then the output would switch on the moment the injector duty cycle is 50% (or greater). The output then stays on until injector duty cycle is 48% (or less). This prevents the drive rapidly switching if injector duty cycle was fluctuating around 50%.

 

Example

If the fan switches on at 95 degrees and the Switch Off Hysteresis is 5 degrees, then the fan will not switch off until the engine coolant temperature falls below 90 degrees.