Sunday, July 5, 2015

Meet the villains of your process alarm system


“Know your enemy and know yourself, and you can fight a hundred battles without disaster.” 
- Sun Tzu (Chinese general and military strategist, c. 6th Century BCE)



Control room operators and system engineers fight their own battles on a daily basis to keep their plant operations in order. However, in many cases they do not have enough clarity and visibility into the problem areas of their SCADA alarm systemNuisance alarm identification and elimination is one such area that deserves some serious attention. In this blog I will talk about the villains of your SCADA alarm system – nuisance alarms.

The ANSI/ISA-18.2-2009 standard defines “nuisance alarms” as follows:

An alarm that annunciates excessively, unnecessarily, or does not return to normal after the correct response is taken.

Let’s dig deeper to know more about these bad actors that make the job of your operators so stressful.

Frequent Alarms: These are alarms that occur quite often. If there are too many frequent alarms in your system, it means either there is something wrong with the facility or the alarm limits you have set. Eliminating the top 10 or 20 of these alarms can help reduce the alarm load significantly. Hence it becomes important to review the most frequent alarms on a daily, weekly or monthly basis.

Chattering Alarm: A typical chattering alarm transitions repeatedly between ON (alarm) and OFF (normal) state in a short period of time. These alarms cause a lot of noise in the system and are the main culprits responsible for operator distraction.

Fleeting Alarms: A fleeting alarm is a type of nuisance alarms that appears and disappears frequently. These alarms are of very short duration, usually too short for the operator to act upon. Unlike a chattering alarm, fleeting alarm does not repeat immediately and this is the main difference between these two alarms.

Standing Alarms: These alarms remain in active alarm state for very long durations even after being acknowledged, sometimes lasting longer than 24 hours. Standing alarms often indicate conditions caused by faulty alarm limits and equipment that might be offline or out of service. These alarms clutter the alarm displays and are a source of continuous distraction to the operator.

Consequential or Cascading Alarms: These are the alarms that are triggered as a result of some other alarm. Technically these alarms do not fall under “nuisance alarms” category; however, these can contribute significantly toward alarm overload. Consequential alarms over a very short period of time often lead to a condition called ‘alarm flood’, which can in turn result in a situation where the operator or engineer would not be able to identify true root causes or problem areas.

Redundant Alarms: Alarms that inform about the same action. Redundant sensors, equipment or instrumentation are the reasons behind these alarms. Alarm shelving is the commonly used alarming technique to manage these alarms.
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An alarm system is like a silent guardian keeping a watch over your plant’s processes, equipment and personnel, and effectively alerting control room operators in case of anomalies and abnormal situations. Identifying and eliminating nuisance alarms is one of the most important aspects of effective alarm management. It can help reduce noise in the control room, improve operator efficiency and facilitate smooth run of your plant processes. Alarm management tools like Wonderware Alarm Adviser can be quite helpful here; visit www.alarmadviser.com and see yourself how this brand new alarm analysis software can help you discover the villains of your SCADA alarm system. Remember, ignorance is the most dangerous enemy. Whether it is a battlefield or a manufacturing facility, knowing the enemy is the first step toward winning.

Nuisance alarm elimination is just one part of a much broader alarm management strategy. Alarm rationalization and auditing are other activities that are equally important. In the future blogs we will talk about rationalization, advanced alarming and industry standards on alarm management.

Special thanks to Suman Singh (sumankumar.singh@schneider-electric.com) who contributed to this article.

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