ALARM-INDICATING DEVICES

Alarm-indicating devices are the lights or sounding devices that indicate a fire alarm or abnormal condition. These lights and sounds may also provide information about where the signal originates.

Indicating devices are divided into two major categories: visual (annunciators) and audible (bells, horns, chimes, and so forth).

Annunciators

Annunciators give a visual indication of the "zone" or general area where an alarm originated. In some cases, such as a sprinkler water-flow alarm, the annunciator can be arranged to identify the individual initiating device. In other cases, such as heat detectors, many initiating devices can activate the same indicator on the annunciator.

The annunciator indicator can be operated directly by auxiliary contacts in the initiating device or from a connection to the fire alarm control unit. A trouble or maintenance condition in the system wiring is also frequently annunciated by zone. Usually, a yellow or amber light indicates trouble and a red light indicates an alarm signal.

An annunciator may be incorporated into the fire alarm control unit, in which case it is generally actuated by connection to the control unit. It may also be located at a remote point, in which case it may be actuated either by the control unit or by auxiliary contacts in the initiating devices. Some installations may have a fire alarm control unit with an integral zone annunciator and a remote annunciator provided elsewhere. Frequently, the control unit standby battery is used to provide power for annunciator operation during power failure.

Annunciator visual indicators may be of the drop type or the lamp type. Those of the drop type (which are essentially obsolete) use electromagnetic devices to move a flag into or away from a window to indicate a change in zone condition. Annunciators of the lamp type use pilot light assemblies to indicate an alarm or trouble condition (usually red for alarm, amber for trouble). The more common type of annunciator in use today is the lamp type. Figure 7-17 shows a frequently used incandescent lamp annunciator.

More recent annunciator designs use matrices or arrays of light-emitting diodes (LEDs). The advantages of LEDs are low current, long life, and small size, allowing annunciation of many zones in a small space.

Figure 7-17.\Remote annunciator (weatherproof)

Audible Signal Devices

Any device that sounds an audible signal is classified as an audible signal appliance. The audible signal appliances most frequently used in building alarm systems are bells and horns. In addition, there are chimes, cowbells, buzzers, sirens, speakers, air horns, and steam whistles. Audible signals can be used to indicate either a fire alarm or a system-malfunction (trouble) condition. The audible signal appliances are connected to audible signal circuits for alarm or trouble indication (depending on their function) at the control unit. Figure 7-18 shows some of the commonly used audible signal appliances.

Audible signal appliances have varying levels of sound output. Louder devices are for areas with high ambient sound levels or where the devices cannot be located near the area to be warned. Hospitals might use softer devices, such as chimes, to avoid frightening patients.

Coded building alarm systems normally use single-stroke versions of bells or chimes so the coded signal can be clearly produced. Vibratory bells, chimes, or horns are used for noncoded systems but can also be used in coded systems if the mechanism used can respond rapidly enough to provide an accurate rendition of the code being transmitted.

In a building that uses audible signals routinely, such as bells for announcing class periods in school, the fire alarm audible appliances must have a distinct, easily identified sound. If the fire alarm signal is coded, the coding provides the distinctive sound, and it is feasible (though not normal) to use the same bells for both functions. For a noncoded fire alarm system, necessary distinction of sound can be obtained by using a completely different type of audible signal appliance, such as a horn or siren, for sounding fire alarm signals.