Annunciator panel

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An annunciator panel, also known in some aircraft as the Centralized Warning Panel (CWP) or Caution Advisory Panel (CAP), is a group of lights used as a central indicator of status of equipment or systems in an aircraft, industrial process, building or other installation. Usually, the annunciator panel includes a main warning lamp or audible signal to draw the attention of operating personnel to the annunciator panel for abnormal events or condition.



The annunciator panel of a Cessna 441 aircraft. The illuminated process annunciators are those that are normally lit when the engines are not running, plus one annunciating that the aircraft's door is not locked
Close-up view of the left module of the Cessna 441 annunciator panel in 'test' mode

In the aircraft industry, annunciator panels are groupings of annunciator lights that indicate status of the aircraft's subsystems. The lights are usually accompanied with a test switch, which when pressed illuminates all the lights to confirm they are in working order. More advanced modern aircraft replaces these with the integrated electronic Engine Indicating and Crew Alerting System or Electronic Centralised Aircraft Monitor.

An aviation annunciator panel will have a test switch to check for burned out lamps. Indicator lights are grouped together by their associated systems into various panels of lights. [1]

Lamp colours are normally given the following meanings:

The annunciator panel may display warnings or cautions that are not necessarily indicative of a problem; for example, a Cessna 172 on its after-landing roll will often flicker the "Volts" warning simply due to the idle throttle position and therefore the lower voltage output of the alternator to the aircraft's electrical system.

More complicated aircraft will feature Master Warning and Master Caution lights/switches. In the event of any red or yellow annunciator being activated, the yellow or red master light, usually located elsewhere in the pilot's line of sight, will illuminate. In most installations they will flash and an audible alert will accompany them. These "masters" will not stop flashing until they have been acknowledged, usually by pressing the light itself, and in some cases the audible alert will also continue until this acknowledgement. On some aircraft (most Boeing airliners, for example) the "masters" will also flash briefly and the audible alert will sound whenever the autopilot is disconnected, as an additional reminder to the pilots that manual control is now required.

Process control

In industrial process control, an annunciator panel is a system to alert operators of alarm conditions in the plant. Multiple back-lit windows are provided, each engraved with the name of a process alarm. Lamps in each window are controlled by hard-wired switches in the plant, arranged to operate when a process condition enters an abnormal state (such as high temperature, low pressure, loss of cooling water flow, or many others). Single point or multipoint alarm logic modules operate the window lights based on a preselected ISA 18.1 or custom sequence.

In one common alarm sequence, the light in a window will flash and a bell or horn will sound to attract the operator's attention when the alarm condition is detected. The operator can silence the alarm with a button, and the window will remain lit as long as the process is in the alarm state. When the alarm clears (process condition returns to normal), the lamps in the window go out.

Alarm Annunciator used for process controls Datmeltech Alarm Annunciator 2.jpg
Alarm Annunciator used for process controls
Alarm Annunciators being used in electricity distribution substations Annunciator Substation.jpg
Alarm Annunciators being used in electricity distribution substations
Example of an Alarm Annunciator that would be used in a variety of different plants Apex Annunciator.jpg
Example of an Alarm Annunciator that would be used in a variety of different plants

Annunciator panels were relatively costly to install in a plant because they had dedicated wiring to the alarm initiating devices in the process plant. Since incandescent lamps were used, a lamp test button was always provided to allow early detection of failed lamps. Modern electronic distributed control systems usually require less wiring since the process signals can be monitored within the control system, and the engraved windows are replaced by alphanumeric displays on a computer monitor. [2]

Behavior of alarm systems, and colors used to indicate alarms, are standardized. Standards such as ISA 18.1 or EN 60073 simplify purchase of systems and training of operators by giving standard alarm sequences.

Obsolescence and revival

The introduction of computer monitor based control systems during the 1980s and 1990s saw a wholesale absorption of alarm window displays onto the computer screen. This created a downturn in the sales of the conventional Alarm Annunciator systems, and many of the companies manufacturing these alarm annunciator products were either sold off or went out of business. This has left today a major obsolescence support problem for customers who are still using these Alarm Annunciator systems as part of their safety systems.

Over the last five years the Alarm Annunciator has seen a resurgence in popularity especially for use in IEC 61508 SIL 1 and SHE (Safety Health and Environmental) alarm monitoring applications. [ citation needed ] The modern trend is to identify critical alarms and return them from the computer screen to discrete alarm windows. This is being done for two reasons. Firstly, alarm annunciators offer pattern recognition to the operators in the form of LED alarm fascias instead of just providing an exhaustive list of alarms and events which the operators have to scroll through and in some instances alarms can be overlooked. Secondly, the analysis of plant failure modes is leading to the separation of critical alarm monitoring and process control systems for safety reasons.

Discrete annunciators vs SCADA alarm systems

SCADA systems were formerly[ when? ] considered the preferred alternative to discrete annunciators. A software-based solution, with almost endless ability to analyze, present and process alarms, has the potential for replacing discrete alarms switches altogether.

However, software carries its own reliability risks. Reliance on a software program to trigger an alarm assumes that the analog signal, the programmer's logic code and HMI, the PLC or PC running the programs, and the interaction between all of the above, are all entirely trustworthy. This is exacerbated by frequently changing computer hardware & firmware platforms and the need to modify existing software. Alternatively new annunciator panels are utilizing long lasting and bright LEDs that significantly reduce the cost and maintenance of the panels. These new versions of the traditional system are still preferred over computer based systems especially in critical plants like nuclear power generation, oil and gas.

In addition to the above, the latest annunciator designs now feature clever electronics to give them very high immunity to noise, and can therefore reduce the amount of false alarms due to noise.

Fire alarm panel

In large buildings, a central fire alarm annunciator panel is located where it is accessible to fire-fighting crews. The annunciator panel will indicate the zone and approximate physical location of the source of a fire alarm in the building. The annunciator will also include lamps and audible warning devices to indicate failures of alarm circuits. In a large building such as an office tower or hotel, the fire annunciator may also be associated with a control panel for building ventilation systems, and may also include emergency communication systems for the building.

See also

Related Research Articles

Instrumentation is a collective term for measuring instruments that are used for indicating, measuring and recording physical quantities. The term has its origins in the art and science of scientific instrument-making.

Supervisory control and data acquisition (SCADA) is a control system architecture comprising computers, networked data communications and graphical user interfaces (GUI) for high-level process supervisory management, while also comprising other peripheral devices like programmable logic controllers (PLC) and discrete proportional-integral-derivative (PID) controllers to interface with process plant or machinery. The use of SCADA has been considered also for management and operations of project-driven-process in construction.

Alarm device Type of signal (or device) that alerts people to a dangerous condition

An alarm device is a mechanism that gives an audible, visual or other kind of alarm signal to alert someone to a problem or condition that requires urgent attention.

A distributed control system (DCS) is a computerised control system for a process or plant usually with many control loops, in which autonomous controllers are distributed throughout the system, but there is no central operator supervisory control. This is in contrast to systems that use centralized controllers; either discrete controllers located at a central control room or within a central computer. The DCS concept increases reliability and reduces installation costs by localising control functions near the process plant, with remote monitoring and supervision.

Dead mans switch

A dead man's switch is a switch that is designed to be activated or deactivated if the human operator becomes incapacitated, such as through death, loss of consciousness, or being bodily removed from control. Originally applied to switches on a vehicle or machine, it has since come to be used to describe other intangible uses, as in computer software.

Fire alarm notification appliance

A fire alarm notification appliance is an active fire protection component of a fire alarm system. A notification appliance may use audible, visible, or other stimuli to alert the occupants of a fire or other emergency condition requiring action. Audible appliances have been in use longer than any other method of notification. Initially, all appliances were either electromechanical horns or electric bells, which would later be replaced by electronic sounders. Most of today's appliances produce sound pressure levels between 45 and 120 decibels at ten feet.

Engine-indicating and crew-alerting system

An engine-indicating and crew-alerting system (EICAS) is an integrated system used in modern aircraft to provide aircraft flight crew with instrumentation and crew annunciations for aircraft engines and other systems. On EICAS equipped aircraft the "recommended remedial action" is called a checklist.

Alarm management is the application of human factors along with instrumentation engineering and systems thinking to manage the design of an alarm system to increase its usability. Most often the major usability problem is that there are too many alarms annunciated in a plant upset, commonly referred to as alarm flood, since it is so similar to a flood caused by excessive rainfall input with a basically fixed drainage output capacity. However, there can also be other problems with an alarm system such as poorly designed alarms, improperly set alarm points, ineffective annunciation, unclear alarm messages, etc. Poor alarm management is one of the leading causes of unplanned downtime, contributing to over $20B in lost production every year, and of major industrial incidents such as the one in Texas City. Developing good alarm management practices is not a discrete activity, but more of a continuous process.

Security alarm System that detects unauthorised entry

A security alarm is a system designed to detect intrusion, such as unauthorized entry, into a building or other areas such as a home or school. Security alarms used in residential, commercial, industrial, and military properties protect against burglary (theft) or property damage, as well as personal protection against intruders. Security alerts in neighborhoods show a connection with diminished robbery. Car alarms likewise help protect vehicles and their contents. Prisons also use security systems for the control of inmates.

Electronic flight instrument system Display system in an aircrafts cockpit which displays flight information electronically

In aviation, an electronic flight instrument system (EFIS) is a flight instrument display system in an aircraft cockpit that displays flight data electronically rather than electromechanically. An EFIS normally consists of a primary flight display (PFD), multi-function display (MFD), and an engine indicating and crew alerting system (EICAS) display. Early EFIS models used cathode ray tube (CRT) displays, but liquid crystal displays (LCD) are now more common. The complex electromechanical attitude director indicator (ADI) and horizontal situation indicator (HSI) were the first candidates for replacement by EFIS. Now, however, few flight deck instruments cannot be replaced by an electronic display.


A push-button or simply button is a simple switch mechanism to control some aspect of a machine or a process. Buttons are typically made out of hard material, usually plastic or metal. The surface is usually flat or shaped to accommodate the human finger or hand, so as to be easily depressed or pushed. Buttons are most often biased switches, although many un-biased buttons still require a spring to return to their un-pushed state. Terms for the "pushing" of a button include pressing, depressing, mashing, slapping, hitting, and punching.

Fire alarm control panel

A fire alarm control panel (FACP), fire alarm control unit (FACU), or simply fire alarm panel is the controlling component of a fire alarm system. The panel receives information from devices designed to detect and report fires, monitors their operational integrity and provides for automatic control of equipment, and transmission of information necessary to prepare the facility for fire based on a predetermined sequence. The panel may also supply electrical energy to operate any associated initiating device, notification appliance, control, transmitter, or relay. There are four basic types of panels: coded panels, conventional panels, addressable panels, and multiplex systems.

Building automation

Building automation is the automatic centralized control of a building's HVAC, electrical, lighting, shading, Access Control, Security Systems, and other interrelated systems through a Building Management System (BMS) or Building Automation System (BAS). The objectives of building automation are improved occupant comfort, efficient operation of building systems, reduction in energy consumption, reduced operating and maintaining costs, increased security, historical performance documentation, remote access/control/operation, and improved life cycle of equipment and related utilities.

Emergency vehicle equipment

Emergency vehicle equipment is any equipment fitted to, or carried by, an emergency vehicle, other than the equipment that a standard non-emergency vehicle is fitted with.

Tell-tale (automotive)

A tell-tale, sometimes called an idiot light or warning light, is an indicator of malfunction or operation of a system, indicated by a binary (on/off) illuminated light, symbol or text legend.

Front panel

A front panel was used on early electronic computers to display and allow the alteration of the state of the machine's internal registers and memory. The front panel usually consisted of arrays of indicator lamps, digit and symbol displays, toggle switches, dials, and push buttons mounted on a sheet metal face plate. In early machines, CRTs might also be present. Prior to the development of CRT system consoles, many computers such as the IBM 1620 had console typewriters.

Industrial control system (ICS) is a general term that encompasses several types of control systems and associated instrumentation used for industrial process control.

A gas detector is a device that detects the presence of gases in an area, often as part of a safety system. A gas detector can sound an alarm to operators in the area where the leak is occurring, giving them the opportunity to leave. This type of device is important because there are many gases that can be harmful to organic life, such as humans or animals.

Stack light

Stack lights(aka: signal tower lights, indicator lights, andon lights, warning lights, industrial signal lights, or tower lights) are commonly used on equipment in industrial manufacturing and process control environments to provide visual and audible indicators of a machine's status to machine operators, technicians, production managers and factory personnel. It is a form of andon - systems in manufacturing which identify errors as they happen.

IEC 62682 is a technical standard titled Management of alarms systems for the process industries.


  1. Photos: British Aerospace BAe-146-200A Aircraft Pictures |
  2. Béla G. Lipták (ed), Instrument engineers' handbook: Process software and digital networks, Volume 3, CRC Press, 2002 ISBN   0-8493-1082-2, page 289