Managing alarms effectively
Many SCADA systems have built-in features that can be used to improve alarm handling, operator response times, and root cause analysis
Has managing alarms at your facility become a problem? Are operators missing critical alarms that could lead to unscheduled downtime or incidents because they’re inundated with too many low-priority alarms? Once alarms are acknowledged, does it take too long to find the root cause?
Conditions change continually in a manufacturing or process plant. Some changes are routine, such as when a motor stops or starts in response to normal operations. Others can be mission critical, such as a temperature rising above maximum limit. Operators are constantly monitoring conditions to prevent problems and achieve maximum efficiency and productivity.
Benefits of using an alarm management system include:
- Ensure critical alarms get a timely response
- Avoid operator fatigue from too many low-level alarms
- Send real-time data to operators for immediate response
- Get detailed information from alarm worksheets
- Identify root causes quickly through alarm filters with string tags.
The introduction of computer-based SCADA systems and the great technological leaps that followed have significantly reduced the cost of alarming, making it almost free to add an alarm point. Most plants are controlled by one or more automation systems, and these systems provide a wealth of data to the SCADA system, data that can be used to monitor nearly every aspect of a plant’s operation. With modern automation and SCADA systems, alarms can be added to a screen without incurring the expense of adding a hardwired alarm point and a panel-mounted indicating device.
While nearly free alarms can provide great benefits, care must be taken in SCADA system design each time an alarm point is added. For example, adding too many alarms can create alarm fatigue for operators who may be distracted by low-priority items at the expense of identifying the root cause problem.
A SCADA system should clearly show appropriate alarms indicating possible problems, but it shouldn’t cry wolf for every routine change in plant operations. It’s easy to blame the SCADA system for alarm overload and other alarm-related issues, but it’s only a tool. Plant personnel need to use this tool correctly by selecting and implementing systems that avoid alarm overload while making sure critical events are addressed in a timely fashion.
Creating an alarm management system
The key to preventing alarm flooding from distracting operators is a proper design of the SCADA system, specifically its alarm handling features. A well-designed system will prioritize alarms to prevent serious alarms from being overlooked as a result of an alarm overload involving a large number of low-priority alarms. It will also offer other advantages, such as the ability to more easily diagnose the root cause of a problem.
The first step in designing a SCADA alarm system is developing a comprehensive plan that determines alarm criteria. This design step should be accomplished with a team consisting of plant operators, plant engineers, and others who have a deep understanding of how the plant actually works. This team will determine and document:
- How alarms should be prioritized
- What type of operator intervention is required for each alarm
- How much time should be allowed for an operator to respond to an alarm
- Operator alarm handling and escalation procedures
- How to structure the system to handle various routine alarms.
The importance of alarm limits in configuration
Most modern SCADA systems are PC-based, and the selected system should include built-in features to allow low-cost and straightforward implementation of an effective alarm management regime. A properly designed SCADA-based alarm management system should help operators distinguish between high-priority and low-priority alarms, respond properly to each alarm, and quickly determine alarm root cause. The alarm management system should contain tools to implement these features—including, but not limited to, configurable alarm limits, alarm displays, and most importantly, filters.
When selecting a new SCADA system it’s important to look for features that will make it possible to prioritize alarms and messages by setting limits and providing sorting capabilities. Creating worksheets with alarm limits is one of the best ways to begin the alarm management process. Alarm limits define high and low values along with deviation set points, creating betting alarm management by helping operators to quickly determine the alarm priority with a glance at the screen.
These alarm limits can be properties of tags, and shouldn’t count against the total number of tags in the SCADA system. This is important as SCADA software is often priced based on total tags.
For example, a tag can be created called “Temperature” that has a setpoint value of 100 degrees. The HiLimit tag property might be set at 110 degrees, and the LoLimit tag property might be set at 90 degrees.
When creating alarm limits, some or all of the following items are typically included:
- HiLimit, the first high alarm point reached on an increasing value
- HiHiLimit, the second high alarm point reached on an increasing value, indicating an escalating condition
- LoLimit, the first low alarm point reached on a decreasing value
- LoLoLimit, the second low alarm point reached on a decreasing value, indicating an escalating condition
- DevSetpoint (Deviation), the allowable deviation or variation above and below the desired setpoint
- Dev+Limit, the allowable deviation plus the alarm limit
- Dev-Limit, the allowable deviation minus the alarm limit
- DeviationDeadband, the range through which a deviation can occur without initiating an alarm.
There are many ways to set alarm limits and display them. Alarm limits can be set for each of the items listed above, and more. Alarm limits can be displayed on SCADA screens using numerical values, or via graphical representations such as sliders. With many SCADA systems, alarm limits can also be saved in separate worksheets with tag names, making it easy to view and adjust settings as necessary.
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