Alarm Management

DOE-HDBK-1132-99

DCSs offer a single, unified, system-wide global database and superior peer-to-

peer communications. By virtue of their configurations, PLCs require a third-

party, PC-based software package (which is generally included with the PLC) to

provide the user with a working operator interface.

DCS offers single source, system-wide support through available service

contracts with dedicated field service personnel. On the other hand, PLC

manufacturers generally do not provide total system service, especially when a

facility uses different PLC manufacturers. The user should support the system or

find a qualified system integrator to provide similar service and support.

Hybrid PLC-DCS control systems may be considered where DCS provides

analog control and operator interface, and PLC provides digital control for motor

and air operated valves, etc.

Alarm Management . The following guidelines for alarm selection strategy should be

4.4

considered:

Provide a systematic approach for identifying, verifying, prioritizing, and

documenting the requirements for process alarms.

Provide capability of alarm pattern recognition and suppression of alarms by

group, status, function, or mode.

Provide an alarm only when the operator is required to take action to avert an

abnormal event. Other information and status can be presented to the operator

in the form of an alert or advisory notice, but should not sound an alarm. Alarms

should be presented to the operator in an organized and optimized manner to

reduce the confusion caused by multiple alarms.

To prevent a single event from causing a cascading of alarms, report alarms

hierarchically to the operator.

Provide capability to advise the operator of the appropriate response to an alarm

or to trigger an automatic response.

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