Working principle of ionization sensor:
In the sensor of ionization type smoke alarm, a small amount of α radioactive substance (am241) is between two charged plates. Under the impact of α particles, the air causes ionization and produces a large number of positively charged ions and electrons. When a certain voltage is applied at both ends of the ionization chamber, the positive and negative ions in the air move towards the opposite electrode to form a current. Once smoke enters the ionization chamber, If the normal movement of charged particles is disturbed, the current will change. The detection circuit amplifies the electrical signal of the change, and when the change reaches the alarm point, the alarm will enter the alarm state.
Principle of photoelectric smoke sensor:
Photoelectric smoke alarm is composed of infrared light-emitting tube, infrared induction tube and a darkroom. In the absence of smoke, the light of the infrared light-emitting tube cannot reach the infrared light sensing tube. When there is smoke entering the small dark room, these small smoke particles cause the light emitted by the infrared light-emitting tube to scatter, resulting in part of the light being received by the infrared sensor tube and converted into an electrical signal. The detection circuit amplifies the electrical signal, and when the alarm point is reached, the alarm enters the alarm state.
There are two types of pre fire combustion:
Smoldering type
Smoldering fires do not produce flame, they produce larger smoke particles (3 to 5 microns), smoldering fires produce slower flow and dispersion of smoke. Because these kinds of fires burn very slowly and the smoke diffuses very slowly, these smoke particles have enough time to stick to each other and combine, just like the smoke particles grow up. In this way, the smoke particles will become larger. The larger smoke particles have a strong diffusion of light, so the photoelectric detection technology can be used to detect such fires.
Open fire type
Flames (open flames) exist in all kinds of fires, and produce a large number of extremely small smoke particles (which may have negatively charged ions). These particles are very small, (0.5-3 microns), which are invisible to the human eye. For example, the smoke produced by natural gas combustion is this kind of smoke. The detection of open fire (fast burning fire) using the ion type smoke alarm has a better effect.