Different alarm types become active under different circumstances.
Alarms types and when they activate include:
Activates when the Boolean value of the monitored variable is not the normal value.
Monitor a variable for the open or closed status of a firewall. An alarm event occurs if the closed normal condition is not met.
Activates when the value of the monitored variable reaches one or more limits of interest.
Monitor temperature. If the low limit is 10 °C and the high limit is 100 °C, an alarm event occurs when the temperature reaches either limit.
Activates when the value of the monitored variable reaches an offset equal to or greater than the set variable.
Monitor a temperature that must be kept constant. If a setpoint value is set to 50 °C, and the temperature drop limit is -3, and temperature increase limit is +3, an alarm event occurs when the temperature reaches either 47 °C or 53 °C.
Activates when the change rate of the value of the monitored variable reaches one or more set limits.
Monitor the value of a variable that represents the speed of a conveyor belt. The variable will be polled every five seconds and the change limit is set to 10. If the measurement shows that the rate of change of the conveyor belt speed is greater than or equal to 10 when compared to the previous sample value, an alarm event occurs.
Signals all corresponding levels up to four levels when several limits of interest are reached consecutively. Levels include low-low, low, high, and high-high.
If a temperature that starts from a normal value reaches the high-high level, an alarm event signals both the high-high and high level.
Signals only the last of up to four levels reached when several limits of interest are reached consecutively.
If a temperature that starts from a normal value reaches the high-high level, the alarm signals only the high-high level.
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