Heat detector can either work on a fixed temperature basis, where it will trigger an alarm if the temperature exceeds a pre-set value or they can work on the rate of change in temperature.
Commonly Heat detectors work in a similar way to an electrical fuse, the detectors contain a eutectic alloy which is heat sensitive when a certain temperature is reached the alloy turns from a solid to a liquid which in turn triggers the alarm.
There are three basic types of smoke detectors including:
– Ionization
– Light Scattering
– Light Obscuring
Ionization Smoke detector generally contains two chambers. The first is used as a reference to compensate for changes in ambient temperature, humidity or pressure. The second chamber contains a radioactive source, usually alpha particle, which ionizes the air passing through the chamber where a current flows between two electrodes.
The light scattering smoke detector operates on the Tyndall effect; a photocell and light source are separated from each other by a darkened chamber such that the light source does not fall on the photocell. The passage of smoke into the chamber causes the light from the source to be scattered and fall on the photocell. The photocell output is being used to initiate an alarm.
In the Light obscuring smoke detector, smoke interferes with a light beam between a light source and photocell. The photocell measures the amount of light it receives. The variation in photocell output, is being used to initiate an alarm.
The Multi-sensor detectors combine inputs from both optical and heat sensors and process them using a sophisticated algorithm built into the detector circuitry.
When polled by the control panel the detector returns a value based on the combined responses from both the optical and heat sensors. They are designed to be sensitive to a wide range of fires.
Manual Fire Alarms
A Manual Call Point or Break Glass Call Point is a device which enables personnel to raise the alarm by breaking the frangible element on the fascia; this then triggers the alarm.