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Types of Smoke Alarm Sensors

Types of Smoke Alarm Sensors

The types of smoke sensors are ion smoke sensors, photoelectric smoke sensors and gas-sensitive smoke sensors.

1. Ionic smoke sensor

The smoke alarm uses ionized smoke sensing inside. The ionized smoke sensor is a technologically advanced, stable and reliable working sensor, which is widely used in various fire alarm systems.

It has a radioactive source of americium 241 inside and outside the ionization chamber, ionization produces positive and negative ions, each moving to the positive and negative electrodes under the action of the electric field. Once there is smoke fleeing the outer ionization chamber. Interfere with the normal movement of charged particles, the current, voltage will change, disrupting the balance between the inner and outer ionization chamber, so the wireless transmitter sends out a wireless alarm signal to notify the receiving host at a distance, the alarm information will be transmitted. This type of detector will be generated by the formation of uncharged particles after ionization charged particles (ions), so called ion-type smoke detectors.

The air between the electrodes is modulated by DC voltage, and the ions are formed with the help of the radiation source, and the current is generated. Smoke particles attached to ions, the current signal is weakened, and this signal changes in proportion to the amount of smoke particles. Ion detector is suitable for the detection of open fires.

2. Photoelectric smoke sensor

Photoelectric smoke alarm inside an optical maze, installed with infrared pair of tubes, no smoke when the infrared receiver tube does not receive infrared light from the infrared transmitter tube, when the smoke enters the optical maze, through refraction, reflection, the receiver tube receives infrared light, intelligent alarm circuit to determine whether the threshold value is exceeded, if more than the alarm.

3. Photoelectric smoke detector can be divided into subtracted light and scattered light type.

A. Light reduction type photoelectric smoke detector

The detector's detection chamber is equipped with light-emitting devices and light-receiving devices. Under normal circumstances, the light device receives a certain amount of light emitted by the light-emitting device; and when there is smoke, the light-emitting device emits light to be blocked by smoke, so that the light received by the light device reduces the amount of light, light current is reduced, the detector issues an alarm signal.

B. Scattered light type photoelectric smoke detector

The detector is also equipped with a light-emitting device and a light-receiving device inside the detection chamber. Under normal circumstances, the light-receiving device does not receive the light from the light-emitting device, and therefore does not produce photocurrent. In case of fire, when smoke enters the detection chamber, the light emitted from the light-emitting device is diffused due to the effect of smoke particles, and this diffused light is received by the light-receiving device, so that the impedance of the light-receiving device changes and a photocurrent is generated, thus realizing the function of converting the smoke signal into an electrical signal, which is then received by the detector to determine whether an alarm signal needs to be issued.

The internal structure of this type of sensor (detection cavity) is set up with optical sensors (emitting light source and photoelectric receiver), smoke into the detection cavity will block the light emission and scattering, photoelectric receiver will receive the signal due to light scattering and change, and then produce a change in the current signal.

4. Gas-sensitive smoke sensor

A gas sensor is a sensor that detects a specific gas. It mainly includes semiconductor gas sensors, contact combustion gas sensors and electrochemical gas sensors, etc., of which the most used is the semiconductor gas sensor. Its applications are mainly: detection of carbon monoxide gas, detection of gas gas, detection of gas, detection of Freon (R11, R12), detection of ethanol in breath, detection of bad breath in human mouth, etc.

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