Smoke point detectors – Smoke point detectors react following the spread of smoke in their study environment, constantly monitor changes in the luminous flux it. Detector is activated at variance above a certain threshold level of light from smoke particles caught in the sensor device – smoke chamber. The latter consists of light source (LED) and photo-receiver, not directly visible to each other. In the ingress of smoke particles in the photo-receiver chamber, reflected light beams fall onto the receiver. The higher the concentration of smoke particles in smoke chamber, the more variation in light flux due to scattering of light rays. The source of light in modern smoke point detectors operate in pulse mode of light emission, which provides low power consumption, longer life and better resistance to confounding factors. This type of detectors are characterized by high sensitivity.
Point temperature detectors – These detectors measured temperature values and changes. Most often include sensor element – thermistor, which is thermosensitive semiconductor resistor, responding to temperature changes. European Standard EN54 categorize temperature detectors depending on the time and the maximum temperatures of bedding.
Maximum temperature detectors thermocouple (fixed temperature) – activated at elevated temperature above a predetermined threshold. They are suitable for use only in cases where slow temperature increase is expected. Otherwise the detector will be triggered too late, when the room temperature is significantly higher than that of bedding.
Thermo-differential detectors – respond to rapid change in the temperature. Usually are with combined action – activated when a certain temperature is reached and at exceeded rate of increase in temperature above a predetermined limit. These detectors are not effective at very slow changes of temperature.
Multi-sensor (combined) point detectors – They react to more than one of the parameters associated to fire, by combining two or three sensors in a detector. Usually thermo-optic chamber is combined with temperature element. These detectors are activated when bedded in either of the sensors and allow further reduction of false bedding.