Dedicated Alarm Annunciator Panel Evolution - Deserve Renewed Attention

Dedicated Alarm Annunciator Panel Evolution - Deserve Renewed Attention

By Robert Myles

Years ago, dedicated Alarm Monitoring systems with windowed panels were being replaced in favor of PLC/DCS systems with CRT Displays and Monitors for a variety of expressed reasons:

  • Annunciator Panel installations seemed costly, especially where all contact wiring had to be brought to a central location and approved cabling is expensive. 
  • Display panels took up too much space so Control Rooms had to be larger.
  • The lamps they used required routine maintenance. 
  • But the most successful selling angle of all: dedicated alarm systems were not useful for control applications, while PLC/DCS systems could perform both the control and monitoring roles. 

At that time, these seemed like perfectly reasonable arguments—especially the last one.  However, as has been observed in many areas, just because you can do something does not mean that you should!

Dedicated Sequence of Events Recorder + Lamp Box System with DCS

PLC/DCS Disadvantage:

PLC/DCS systems came under the jurisdiction of the Engineering groups and included software engineers who well understood the systems they programmed, but who did not always understand the processes they were monitoring and controlling.  Many events were assigned as alarms or warnings simply because it was easy to do so, leaving it up to the operators to deduce the reason that the alarm occurred and what to do in response.  This resulted in many nuisance alarms that operators learned to ignore, contributing to operator apathy.  When emergency conditions occurred, tens or even hundreds of alarm and warning messages might be displayed, a condition referred to as alarm flooding.  It was the job of the operators to determine which were significant and which could be ignored, often overwhelming the operators with disastrous results.  Moreover, as greater numbers of contacts were being monitored, it was not uncommon for distributed networks to become overloaded with the alarm event reports, thus significantly impacting the response times of the control messages that shared the same paths.  For these reasons, it has become clear that PLC/DCS systems are excellent choices for process monitoring and control, but not the most reliable choices for alarm management.

Over time, an interesting pattern has emerged: in plants where a dedicated, annunciator panel is used in conjunction with PLC/DCS systems, many operators tend to trust the panel to know when and how to respond.  They may use the detailed information available from the PLC/DCS to augment their reaction to the event; but the panel triggers their responses.  So effective is this combination that safety specifications recommend that installations include a dedicated alarm annunciator panel for their most safety critical alarms.  

A New Discipline is Born:

The problem grew to the level that specialized, independent, Alarm Management systems and safety practices dedicated to identifying, prioritizing and handling alarm events to prevent shutdowns and catastrophes were developed.  In fact, it became so prevalent that in 1994, a consortium of manufacturers and industry partners (e.g. Honeywell, Shell Oil) in conjunction with the U.S. Government (NIST) and various universities formed the Abnormal Situation Management (ASM) Consortium whose charter it is to research methods to operate plants at their highest levels of efficiently while maximizing safety and minimizing environmental impact that abnormal situations create.  This group has determined that most traditional DCS systems are not designed to IEC 61508 standards and should not be used for Safety Critical Alarm Management.

Consider Dedicated Annunciator Panels:

A careful review of the Alarm System specifications vis-à-vis any number of specifications (e.g. IEC 61508) reveals attributes that many modern, dedicated, annunciator panels easily meet—especially those that are SIL certified.  They also offer an excellent means for achieving independent, redundant, alarm and data collection to meet regulatory compliance or best practice corporate policies. 

Annunciator Panels in a Modern System:

The following attributes of Dedicated Alarm Annunciator Panels show that the original reasons for replacing them have largely evaporated.  For example:

  • Many Annunciator Panels are networked.  They can be installed adjacent to the process area they monitor while exporting alarm events via serial networks to remote systems, vastly reducing the wiring required and the cost per point.
  • They are scalable and interoperable
  • They are rugged and reliable.  Annunciator systems are available with different mountings and NEMA enclosures for indoor and outdoor applications. Explosion proof annunciators for critical area applications are also available.
  • They are available with LED backlight displays that can be used outdoors where LCD/LED panels cannot.  LEDs also require far less maintenance in most environments.  Lamps are still available for the harshest.
  • Many Annunciator Panels provide IRIG-B or GPS-based Time Stamping of events for event recording at 1 millisecond sampling rates.
  • Dedicated Annunciator Panels provide unambiguous signaling of alarm conditions with higher visibility angles than typical LCD/LED displays.
  • Dedicated Annunciator Panels do not require programming.  The typical field maintenance technician can easily connect and configure an alarm point.
  • Many Annunciator systems support the same protocols as their PLC/DCS counterparts (DNP 3, OPC, Modbus, etc.).  Thus, they can serve as auxiliary data sampling sources for these systems while maintaining their standalone annunciator functionality.
  • Though networked, the alarm function is independent and dedicated; thus they are impervious to network failures or network attacks.

Conclusion:

Given the issues present in large-scale PLC/DCS systems and the advantages offered by Dedicated Alarm Annunciators, the additional cost to include one as a redundant system is well outweighed; particularly when the system or the process they are protecting and the cost of a shutdown (or worse) is taken into account.

Robert Myles is a guest technical writer for Ronan Engineering Company.

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