What is Alarm system?
An alarm system is a system designed to direct the attention of the operator to significant aspects of the current state of the plant.
Engineering Equipment and Materials Users Association ( EEMUA) issued a publication No. 191 Alarm Systems in 1999. EEMUA is a guideline to design, management and procurement of an ideal alarm system written by major multinational companies in the petroleum, gas, chemical, and power industries.
According to the alarm nature, alarms are classified into:
A fault alarm is an alarm that is reported to the network management team when the computer has faults or exceptions. After faults or exceptions are processed and deleted, the alarm is cleared.
An event alarm is an alarm generated to indicate a transient state during the operation of the equipment. Some event alarms are generated periodically. Event alarms only notify that the system is in an alarm state and, therefore, does not require handling.
Components and properties of alarm management:
The text of the alarm contains a description of the alarm. The character formats supported by the relevant operator panel can be used to format the alarm text on a character-by-character basis.
The alarm text can contain output boxes for the current values of the labels or text lists. The label image retains the instantaneous value at the time the alarm status changes.
The alarm number is used to internally manage an alarm. Each alarm number is unique within the following types of alarms:
Discrete alarms, analog alarms, HMI system alarms, alarms from the controller within a CPU.
The alarm class defines whether the alarm has to be acknowledged or not. It can also be used to determine how the alarm appears when it is displayed on the operator panel. The alarm class also determines if and where the corresponding alarm is recorded.
If an alarm belongs to a group of alarms, it can be confirmed together with other alarms of the same group in a single operation.
Alarm management procedure:
There must be management systems to ensure that the alarm system is operated, maintained and modified in a controlled manner. The operation of the alarm system must be evaluated and monitored to ensure that it is effective during normal and abnormal plant conditions.
Steps for alarm management system:
A design and guidance document is produced that defines a plant standard that uses a best practice alarm management methodology.
Analyze the alarm system to determine its strengths and weaknesses, and effectively plan a practical solution to improve it.
About half of the total alarm load usually comes from relatively few alarms. The methods to make them work correctly are documented and can be applied with minimal effort and maximum performance improvement.
A complete review of the alarm system to ensure that each alarm meets the philosophy of the alarm and the principles of good alarm management.
DCS alarm systems are notoriously easy to change and generally lack adequate security. Methods are needed to ensure that the alarm system does not deviate from its streamlined state.
More advanced alarm management techniques are needed to ensure that the alarm system adequately supports, rather than hinders, the operator in all operational scenarios. These include the Alarm Shelving, State-Based Alarms and Alarm Flood Suppression technologies.
Adequate change management and long-term analysis and KPI monitoring are required to ensure that the gains that have been made from the previous steps do not diminish over time. Otherwise they will; The principle of “entropy” definitely applies to an alarm system.