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), CitectSCADA 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). CitectSCADA 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.
Allowable Values: 1 to 3600 (seconds)
Default Value: 60
See Also