Parent control alarm suppression

Parent control alarm suppression handles alarms by inhibiting alarm events that are a direct and predictable result of a Controller’s command to a field device.

Starting a pump, for instance, results in a pressure wave in the pipe. A pressure sensor further down the pipeline from the pump would likely go into alarm when the pressure wave hits. By configuring the sensor as a child of the pump device, it is possible to inhibit the alarm.

Relationships between parent and child records are configured in the RealTime database’s (RTDB's) Alarm Suppression (almsuppression) table. Extensions that are added to alarm suppression, such as alarm suppression based on state, are also available for parent control alarm suppression. For more information, refer to Timed parent alarm suppression.

When a Controller issues a control command to a Remote Terminal Unit (RTU), for example setpoint, and the command arrives successfully, the alarm suppression (almsuppression) records that have the controlled record as a parent are marked as suppressed. The alarm suppression timeout is set up, and at expiration, the children’s alarm conditions are reevaluated. If, at reevaluation, the child is in a different alarm state from where it was when the parent was commanded, the system generates an alarm. The parent control alarm suppression is then cleared. If the control command failed to execute at the remote, then the alarm suppression timeout is canceled, and any suppressed child alarm is immediately evaluated.

In the figure above, the state of the child goes into alarm shortly after the command is sent to the parent. The child returns to normal at the 100-second mark. If the control suppression timeout is set to a value greater than 100 seconds, then the child will not alarm: it has returned to normal before the alarm suppression timeout expired. If the timeout value were shorter, for instance 90 seconds, then the child alarm would generate after 90 seconds.

Notes: If a parent is commanded while a control suppression timeout is already under way, the control suppression timeout will be reset. However, when the updated alarm suppression timeout value expires, control suppression does not record a new child state value for evaluation.

Only child state alarms that result from data krunching are suppressed by parent control alarm suppression. Other types of alarms (for example, command failure) execute as normal. Parent control alarm suppression is supported for analog, rate, multistate, and status records.

Since rate points do not have associated control commands, you can only configure them as children of almsuppression records whose Suppression Method is Parent Control.