Classification of fire detectors

There are many types of fire detectors. According to different structures, smoke detectors can be divided into ion smoke detectors and photoelectric smoke detectors.

Here is the content list:

l Ion smoke fire detector

l Photoelectric smoke fire detector

Ion smoke fire detector

The ion smoke detector is composed of two series chambers containing Am241 radioactive sources, field-effect transistors, and switch circuits. The inner ionization chamber is the compensation chamber, which is sealed, and the smoke is not easy to enter; the outer ionization chamber, the detection chamber, is perforated, and the smoke can enter smoothly. When a fire occurs, smoke enters the detection ionization chamber, the alpha rays generated by am241 are blocked, the ionization ability of the fire detector decreases, the ionization current decreases, and the equivalent impedance of the air in the detection ionization chamber increases, and the compensation ionization chamber enters the ionization chamber due to no smoke. The impedance of the two ionization chambers remains the same. Consequently, a change in the ratio of the partial pressures applied across the two ionization chambers is induced. When the voltage at both ends of the ionization chamber detected in the fire detector rises to a certain value, the switch circuit operates and an alarm signal is issued.

Photoelectric smoke fire detector

The photoelectric smoke detector is composed of a light source, a photoelectric element, and an electronic switch. Using the principle of light scattering, the smoke generated in the early stage of the fire is detected, and an alarm signal is issued in time. Different light sources can be divided into four types: general photoelectric type, laser photoelectric type, ultraviolet photoelectric type, and infrared photoelectric type. Generally, photoelectric smoke detectors can be divided into two types: shading type and scattering-type according to their structural characteristics. The shading photoelectric smoke detector is composed of a light source and a photoelectric element installed in a small dark room correspondingly. In the case of no smoke, the light emitted by the light source is concentrated into a light beam through the lens, irradiated on the photoelectric element, and converted into an electrical signal, so that the entire circuit is maintained in a normal state and no alarm is issued. When a fire occurs and smoke enters the fire detector, the propagation characteristics of the light are changed, the light intensity is weakened, the normal state of the circuit is destroyed, and an alarm signal is issued. The positions of the light-emitting diodes and the photoelectric elements of the scattering photoelectric smoke detector are not corresponding. The optoelectronic element is set in a small porous dark room. When there is no smoke, the light cannot be emitted to the photoelectric element, and the circuit maintains a normal state. When a fire occurs, smoke enters the fire detector, and the light reaches the photoelectric element through the reflection or scattering of the smoke particles, and the optical signal is converted into an electrical signal, which is amplified by the amplifier circuit to drive the automatic alarm device to issue an alarm signal. Laser smoke detector. It consists of a laser transmitter and a laser receiver. It utilizes the characteristics of strong laser directionality, high brightness, and good monochromaticity and coherence. In the case of no smoke, the pulsed laser beam hits the photoelectric receiver and is converted into an electrical signal, and the fire detector does not alarm.

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