ADEMCO VISTA-100 Service Manual download pdf (Page 9)

Signaling Line Circuit (SLC): A circuit to which initiating and/or notification appliances are connected. The signal

received does identify the individual device operated. Another commonly used term is addressable loop.

Smoke Detectors: Typically, fires that occur in family living units or office buildings produce detectable quantities of

smoke before they produce detectable levels of heat. Therefore, fire alarm system designers use smoke detectors more

extensively today than heat detectors.

Smoke Detector - Ionization: Ionization smoke detectors are more responsive to sensing invisible smoke particles

produced by flaming type fires, like those produced from flammable liquids. An ionization smoke detector has a small

amount of radioactive material that ionizes the air in the sensing chamber, thereby rendering it conductive and permitting a

current flow through the air between two charged electrodes. When smoke particles enter the chamber, they attach

themselves to the ionized air molecules and decrease the conductivity between the electrodes. When the reduction in

conductivity reaches a pre-set threshold, the electronic circuit will initiate a fire alarm signal.

Smoke Detector - Photoelectric: A light source and a photosensitive sensor are arranged so that the rays from the

light source do not normally fall on the photosensitive sensor. When smoke particles enter the light path, some of the light

is scattered by reflection and refraction onto the sensor, causing the detector to initiate a fire alarm signal. Industry experts

agree that photoelectric smoke detectors are usually more responsive to detecting visible particles of combustion from

burning carpet, furniture upholstery and drapes.

Smoke Detector – Two-wire: Two-wire smoke detectors receive their operating power and initiate an alarm from the

same pair of wires, the Initiating Device Circuit (IDC). Because they receive their operating power from the initiating device

circuit, there are two very important considerations when installing them:

• Detector compatibility with a control panel

• Quantity of detectors per initiating circuit.

Smoke Detector – Four-wire: Four-wire smoke detectors receive their operating power and initiate an alarm from

separate circuits. They receive their operating power from an auxiliary power circuit and they initiate an alarm from the

initiating device circuit. The auxiliary power supply for 4-wire units can either be a separate power supply or integral to the

control panel. Either way, the power supply must be UL listed for fire alarm use and be interruptible for smoke detector reset

Speakers: Speakers are generally operated from audio amplifiers housed in the control panel that delivers a standard

output line levels of 70.7 or 25 volts rms. Speakers are driven by an electronic tone generator, microphone, tape player, or

voice synthesizer and an electronic amplifier.

Spot-Type Detector: A device whose detecting element is concentrated at a particular location. Typical examples are

heat detectors and smoke detectors.

Sprinkler Systems: An automatic sprinkler system consists of sprinkler heads located throughout the building that are

connected to a metal piping system. This piping system is connected to the municipal water supply. When heat produced

from a fire reaches a predetermined fixed temperature it will trip the sprinkler head and discharge water from the piping

system to extinguish the fire. The fire alarm system should monitor the operation of automatic sprinkler systems with listed

fire alarm initiating devices such as water flow switches and supervisory switches.

Wet Pipe Systems: Wet pipe systems are the most common. The piping system is filled with water at all times in

wet pipe systems. Water will only discharge though sprinkler heads that have been activated.

Dry Pipe Systems: Dry pipe sprinkler systems are typically used where there is a potential for the water in the

piping system to freeze such as in unheated warehouse spaces or large commercial freezer rooms. Pressurized air is

maintained in the piping system to hold back the water supply. When a sprinkler head is activated and opens, the air

bleeds out thereby lowering the pressure in the piping system and starting the flow of water to the open sprinkler

head. Water will only discharge though sprinkler heads that have been activated.

Water Flow Switches: When a sprinkler head is tripped by heat produced from a fire, water in the piping system

will start flowing, activating the water flow switch. The activated water flow switch will initiate an alarm signal to the

fire alarm control panel.

Glossary of Terms

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ADEMCO VISTA-100 Service Manual Page 9

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