FIRE ALARM SYSTEM

Fire alarm system consist of fire detectors ,manual call points ,Bells ,Fire alarm control panels ,Fire alarm cables .
There are 2 types of fire detectors ,smoke detectors & heat detectors . Also there are 2 kinds of smoke detectors which are ionisation detectors and light scattering detectors .From these 2 types light scattering type detectors are most probably used in construction industry .

Light Scattering smoke detector -:

According to the construction of detector it consist of light source ,reflector and photo cell. The light beam does not fall on to a photo electric cell at normally .When smoke enters the detector , some of the light beam is deflected upwards on to the photo electric cell. An electric current is thus produced which actuates the alarm .

Heat Detector -:

Heat detectors not active as smoke detectors . where the places heat detector use ,smoking is allowed .Some heat detectors have predetermine temperature ,when temperature goes above this predetermine value it's activated .Some heat detectors activate to rate of rise temperature .

Bi-metal coil detector is the popular detector for heat detectors among ELV engineers . In the bi-metal coil detector , heat from the fire passes through the cover to the bi-metal coils and the lower coils receives greater heat initially than the upper coil .The lower coil quickly makes contact with the upperv coil to complete the electricalcircuit and sound the alarm.

Manual call point -:

Manual call point use to awarw peoples about a fire .When fire occurs a person can press m.c.p & run away from fire .Due to this press bells start to ringing .

FAC (Fire Aclarm Control ) Panel -:

FAC panel comprise of software & hardware . FAC panel release signals according to the information it received by the detectors .If there are more than 1 FAC panel ,which are interconnected by network cards .FAC panel works 12v dc voltage .

Cables Used in Fire Alarm Systems -:

Fire cables consist with 2 covers for (+) & (-) and one sheath to obtain noise .The outer insulation layer is withstand to fire .