Alarms

Alarms are conditional statements that can be enabled at any time and can alter the status of a particular phase block. Phase blocks can have any number of alarms. The alarms are found in the alarm section of the program corresponding to the unit or connection with which they are associated. Usually, alarms correspond to an output device.

Two levels of severity are generally associated with alarms for a given set of conditions:

• Advisory alarm

  This alarm may require an acknowledgment by the operator. However, the advisory alarm does not require an operator reset, and usually the phase block does not require a restart command. The block operation continues as normal.

• Critical alarm

  This alarm condition usually requires the operator to acknowledge the alarm, reset the alarm, and restart the phase block. If a particular alarm condition exists, the respective discrete memory location is enabled, the phase block alarm is set, and, if it is a critical alarm, the phase block status may be altered.

  Note: We recommend that, for the safety of process personnel, you configure alarms as critical alarms whenever possible so that the phase block must be manually restarted.

The following are examples of phase block alarms:

• A reactor discharge valve fails to open or close and disrupts the operation of a transfer phase block. This sets an alarm bit that is read by batch control system, and puts the transfer phase block in Held status.

• The agitator does not turn on within a predetermined length of time after the signal to turn on is sent to the starter. This situation also sets an alarm bit that must be addressed by the operator.

• The actual temperature within a reactor exceeds a predetermined value.