Smoke detectors are based on what principle to detect fire

Smoke detector is the use of a small smoke sensor response suspended in the atmosphere around the neighborhood of combustion and (or) pyrolysis smoke aerosol (solid or liquid particles) of a fire detector, according to the principle can be divided into ionic and photoelectric type two kinds.

1, ion smoke detector

Ion smoke detector is the use of ionization chamber ion flow change is basically proportional to the smoke concentration into the ionization chamber to detect the fire. A radioactive source (radioactive element: "Americium-241") in the ionization chamber ionizes the pure air in the chamber, forming positive and negative ions. When a voltage is added between the two collection plates, an electric field is formed between the plates, and under the action of the electric field, the ions move toward the positive and negative plates to form an ion stream. When the smoke particles into the ionization chamber, because the diameter of the smoke particles greatly exceeds the diameter of the ionized air particles. Therefore, the smoke particles in the ionization chamber on the ions to produce the dual role of blocking and capture, thereby reducing the ion flow.

2, photoelectric smoke detector

Photoelectric smoke fire detector is the use of smoke can change the propagation characteristics of light and the development of this basic property. According to the smoke particles on the absorption and scattering of light, photoelectric smoke detectors are divided into two types of light-reducing Lee scattered light type.

Smoke detectors by the light-emitting elements, lens and light components, usually the light source (light-emitting elements) issued by the light, through the lens to the photosensitive elements (light components), the circuit to maintain normal, if there is smoke from the barrier, to reach the photosensitive elements of the light flux will be significantly weakened, the photosensitive elements of the change in light intensity is converted into an electrical signal change. Photocurrent relative to the initial calibration value of the change in the amount of people small, reflecting the concentration of smoke, according to which can be processed through the electronic electrical circuit of the fire information, through the amplification circuit to send out the corresponding fire signal.

Scattered light photoelectric smoke detector by the detection of dark room, light-emitting components, light-emitting components and electronic circuits are composed of. Detection of dark room is a specially designed "maze", the external light can not reach the light-emitting element, but the smoke particles can enter it. In addition, the light-emitting element and the light-receiving element are set at a fixed angle in the detection chamber, and a light shield is set up between them so that the light emitted from the light-emitting element cannot reach the light-receiving element directly. Scattered light photoelectric smoke detector working principle shown in Figure 1-3, smoke particles into the photoelectric smoke detector smoke chamber, the light source inside the detector light is scattered by the smoke particles, and the scattered light is in the optical path side of the photosensitive element sensing. The response of the photosensitive element is related to the size of the scattered light and is determined by the concentration of the smoke particles. If the smoke concentration sensed by the detector exceeds a certain limit, the energy of the scattered light received by the photosensitive element is sufficient to excite the detector to act, thus sending out a fire alarm signal.

Line infrared beam smoke detector is a line in the warning range of a line around the smoke particles to respond to the fire detector, but also belongs to a light-reduced smoke detector, as shown in Figure 1-4. It is characterized by a wide monitoring range and a large protection area. It consists of two separate parts, the transmitter and the receiver, and the optical path for measurement is exposed to the protected space and lengthened many times. If smoke spreads into the measurement area, the smoke particles absorb and scatter the infrared beam, so that the light signal reaching the light-receiving element is weakened. When the light signal is weakened to a certain extent, the detector sends out a fire alarm signal.

Traditional photoelectric smoke detectors use forward scattering light acquisition technology, but there is a big flaw is that the black smoke sensitivity is low, the white smoke sensitivity is high. Since most fires emit black smoke at an early stage, this greatly limits the use of such detectors.