Hysteresis
Deliberately keeping the trip and release values of a threshold different. For example, if protection engages at 30 A and releases at 26 A, the hysteresis is 4 A. Without this difference, when the measured value oscillated right at the threshold the system would switch on and off many times a second and wear out both the load and the switches.
Hysteresis is the simplest method for eliminating the instability a noisy signal creates around a threshold. Once the system has changed state, the signal has to go back by a noticeable amount for it to return.
- Thermal protection: The driver shuts down at a critical temperature, but comes back not after cooling by just a few degrees, rather after cooling by a meaningful difference (typically 10–20 °C). Otherwise it enters an off-on cycle.
- Current threshold: In current-sensing stop, a load hovering just below the threshold produces continuously interrupted motion without hysteresis.
- Digital input: To prevent a slowly changing signal from chattering at the threshold, input stages are most often designed with built-in hysteresis.
Increasing the hysteresis improves stability but coarsens the response. The practical approach is to choose the difference as at least twice the noise amplitude of the signal.
The context in which this term is used: DC Motor Driver Selection Guide