Chapter 3: Using the Web Interface
55
Deassertion Hysteresis:
In the threshold settings, the Deassertion Hysteresis field determines a new level to trigger the "deassertion" action.
This function is similar to a thermostat, which instructs the air conditioner to turn on the cooling system when the
temperature exceeds a pre-determined level. "Deassertion Hysteresis" instructs the PDU to de-assert the worse state for a
sensor only when that sensor's reading reaches the pre-determined "deassertion" level.
For upper thresholds, this "deassertion" level is a decrease against each threshold. For lower thresholds, this level is an
increase to each threshold. The absolute value of the decrease/increase is exactly the hysteresis value.
For example, if Deassertion Hysteresis = 2, then:
•
Upper Critical = 33, so its "deassertion" level = 33 - 2 = 31.
•
Upper Warning = 25, so its "deassertion" level = 25 - 2 = 23.
•
Lower Critical = 10, so its "deassertion" level = 10 + 2 = 12.
•
Lower Warning = 18, so its "deassertion" level = 18 + 2 = 20.
To use each threshold as the "deassertion" level instead of determining a new level, set the Deassertion Hysteresis to 0
(zero).
How "Deassertion Hysteresis" is helpful:
If you have created an event rule that instructs the PDU to send notifications for deassertion events, setting the
"Deassertion Hysteresis" is helpful for eliminating a number of notifications that you may receive in case a sensor's
readings fluctuate around a certain threshold.
Deassertion Hysteresis Example for Temperature Sensors
Assumption:
Upper Warning threshold is enabled.
Upper Warning = 20 (degrees Celsius)
Deassertion Hysteresis = 3 (degrees Celsius)
"Deassertion" level = 20-3 = 17 (degrees Celsius)
