The purpose of hysteresis is to prevent unwanted frequent alarms caused by oscillation of the monitored value around a threshold and to alert the user that the monitored value continues to escalate outside set thresholds.
Hysteresis acts as a secondary threshold, relative to the main threshold. Once in alarm, the Device will stay in that state as long as the measured value does not return within thresholds by the hysteresis value margin. Also, when the measured value continues to rise or drop, above or below the thresholds, the Device will notify users for every hysteresis step further away from the thresholds.
Example: High temperature threshold: 30 °C; Hysteresis setting: 2.
Measured temperature exceeds 30 °C, the Device is in alarm and notifies the user. Temperature continues to rise, the Device notifies the user again when temperature exceeds 32 °C, 34 °C, 36°C etc., every 2 °C. When the temperature starts to drop, the Device will be in alarm (without further notifications) until the temperature drops a hysteresis step below the threshold, in this case 28 °C. Once the temperature drops below 28 °C, user will be notified that the Device is no longer in alarm.
NOTE: Hysteresis setting is limited to be less than the threshold difference, otherwise the Device would be permanently stuck in alarmed state.