Rate of Change Alarms

A rate of change alarm identifies when an attribute value is changing too quickly over time. For example, you can set a rate of change alarm for a tank level that indicates when the pump inlet pressure is too high.

Rate of change is the calculated slope, which is the absolute difference between the current and previous attribute values divided by a specified interval. When the slope (positive or negative) exceeds a specified value, a rate of change alarm occurs. For example, if a tank volume increases from 17 to 45 liters over a 5 minute interval, the calculated slope is 5.6 liters per minute. If you set your rate of change alarm limit to 5.0 liters per minute, a rate of change alarm condition exists.

Alarm limits are expressed in the Engineering Units of the attribute’s value over an interval, which can be per second, minute, hour, or day.

You can select and configure the value and priority for the upward and downward ROC limits. You can set individual messages for ROC alarms that exceed the upward or downward limits.

The timestamp when a rate of change alarm becomes active or inactive is the most current timestamp of the corresponding input value. If there is no timestamp associated with the alarmed value, the AppEngine timestamp is used instead.