General Introduction
The A1R, BR and CR (rate-of-rise) heat detectors opeartae by using
a matched pair of thermistors to sense heat. One thermistor is exposed
to the ambient temperature, the other is sealed. In normal conditions,
the two thermistors register similar temperatures recorded by the
exposed thermistor will increase rapidly. resulting in an imbalance,
causing the detector to change inot the alarm state. Rate-of-rise
detectors are designed to detect a fire as the temperature increases,
but they also have a fixed upper limit at which the detector will
go into alarm if the eate of temperature increase has been too slow
to trigger the detector earlier.
General Introduction
The Sensing part of the detector consists of two chambers - an open,
outer chamber and a semi-sealed refernce chamber within. Mounted
in the reference chamber is a low activity radioactive foil of Americium
241 which enables current to flow between the inner and outer chambers
when the detector is powered up.
An intergrating ionisation detector, suitable for
use in areas where transient levels of smoke may be expected is
also available.
General Introduction
Optical smoke detectors incorporate a pulsing LED located in a chamber
within the housing of the detector. The chamber is designed to exclude
light from any external source. At an angle to the LED is a photo-diode
which normally does not register the column of light from a fire
entering the chamber, the light pulse from the LED will be scattered
and hence registered by the photo-diode.
