[Alarm]Period

The period used to determine when a Rate of Change alarm will be triggered for a variable tag. The Rate specified in Analog Alarm Properties is divided by this period to determine the `maximum rate" at which the value of the variable tag can change. At each Scan Time (see [Alarm]ScanTime), Plant SCADA checks the value of the tag. If its rate of change is greater than the "maximum rate", a Rate of Change alarm is triggered.

For example, if your goal is to minimize the likelihood a tank from filling too quickly, you might configure a rate of change alarm, using an [Alarm]Period of 60 seconds, an [Alarm]ScanTime of 1 second, and a Rate (see above) of 300 liters. This means that the maximum allowable rate of change for the tank level is 5 l/sec (300 liters / 60 seconds). Plant SCADA calculates the actual rate of change at each ScanTime. i.e. every second, it checks the current level of the tank and compares it to the level recorded a second earlier. If the actual rate of change is, say, 8 l/sec, a Rate of Change Alarm is triggered immediately.

Note: This parameter can also be applied to a specific cluster or alarm server process. For more information, see Configure Alarm Parameters for a Specific Cluster or Process.

Allowable Values:

1 to 3600 (seconds)

Default Value:

60

See Also

Alarm Parameters