JAN-FEB 2019

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32 INTECH JANUARY/FEBRUARY 2019 WWW.ISA.ORG AUTOMATION IT The ISA-18.2 technical reports are as follows: l TR1: Alarm Philosophy l TR2: Alarm Identification and Ratio- nalization l TR3: Basic Alarm Design l TR4: Enhanced and Advanced Alarm Methods l TR5: Alarm System Monitoring, As sessment, and Audit l TR6: Alarm Systems for Batch and Discrete Processes l TR7: Alarm Management when Utiliz- ing Packaged Systems An eighth technical report, TR8: Alerts, Events, Prompts, and Other No tifications, is currently under devel- opment. Four of the technical reports, TR1, TR2, TR3, and TR5, are focused around specific ISA-18.2 life-cycle work processes. The other three, TR4, TR6, and TR7, cover how to apply alarm man- agement in a number of special applica- tions, and are the focus of this article. TR4: Enhanced/advanced alarms TR4 gives guidance on how and when to use enhanced and advanced alarm methods. In ISA-18.2, alarms are bro- ken into two categories: basic alarms and en hanced/advanced alarms. Basic alarms typically consist of a set point or a trigger value, plus on-delay, off-delay, and/or deadband, but have no addition- al logic associated with them. The term "enhanced/advanced alarm" is used for alarms that use special features or pro- gramming. Although both basic and en- hanced/advanced alarms are discussed in ISA-18.2, enhanced/advanced alarming methods are not required in all cases, and are discussed in less detail in the standard. In general, application of the basic alarm practices in ISA-18.2 (as well as in TRs 1, 2, 3, and 5) will improve the valid- ity and consistency of alarm design, avoid inappropriate alarms, and establish long- term viability for most alarm systems. However, the dynamic nature of some processes and related process complexi- ties can lead to the alarm system objec- tives being only partially met using basic alarm design approaches. For example: l Alarm floods, though reduced, may still occur. Individual process events can cause multiple alarms at roughly the same time for a single underlying process event. l A process may have other operating states in addition to the normal steady state, or it may have multiple nor- mal operating states. This means that alarms have to be designed to accom- modate multiple operating states, each of which may need different alarms and/or alarm set points. l Basic alarm capabilities may not deliver the alarm to the person who needs to respond to it on the operat - ing team. Enhanced methods may be needed to route an alarm to the ap- propriate person. The difficulty with using enhanced and advanced alarm methods is that they do add complexity to the alarm system and can be time consuming (and con - sequently costly) to implement. Thus, enhanced/advanced alarms should be reserved for only those situations that truly need them. It is important to first reduce the scope of any enhanced/ad - vanced alarming effort by using basic rationalization and basic alarm design approaches as much as possible. TR4 provides guidance and examples on the selection, design, and implemen- tation of enhanced/advanced alarm methods. Specific situations in a number of areas are discussed, along with solu- tion methods and examples. Some of the topics covered by TR4 include: Dynamic alarm attributes: Various examples are provided for where alarm attributes are automatically and dynam - ically changed by the control system based on the current operating state of a process. In fact, both the advanced/ enhanced alarming TR4 and the batch- process oriented TR6 have multiple ex- amples of dynamic alarm attributes. Information linking: Information em- bedded in the alarm itself (e.g., tag, de- scription, and set point) may not always be enough to help guide the operator's response. Often the appropriate guid - ance has already been identified during the alarm rationalization stage but not built into the primary alarm presenta - tion. Information linking within the alarm system can be used to present additional information to an operator when an alarm is triggered. State-based alarming: A number of methods are discussed for handling alarms during changing the plant state and operating conditions in order to minimize alarm floods or inappropriate alarms. This can occur for planned oper- ating states, such as startup, shutdown, batch phases, and different feedstocks; or it can occur due to unplanned events, such as a compressor trip. Techniques discussed include: first-out alarming, designed suppression, state-driven alarm attribute changes, and dynami- cally calculated alarm set points. Figure 2 shows an example of calculated alarm set points, which is touched on in TR4 and Figure 2. An example of advanced alarming for a batch process (figure 15 from TR6)

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