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Sep 27,2021

What are the principles of smoke detectors, gas detectors, and carbon monoxide detectors?

From an internal principle perspective, smoke alarms achieve fire prevention by monitoring the concentration of smoke.

Smoke detector: Smoke detector

From an internal principle perspective, smoke alarms achieve fire prevention by monitoring the concentration of smoke. It has a radioactive source of americium-241 inside and outside the ionization chamber, and the positive and negative ions generated by ionization move towards the positive and negative electrodes under the action of an electric field. Under normal circumstances, the current and voltage inside and outside the ionization chamber are stable. Once smoke escapes from the outer ionization chamber. Interference with the normal movement of charged particles causes changes in current and voltage, disrupting the balance between the inner and outer ionization chambers. As a result, the wireless transmitter emits a wireless alarm signal to notify the remote receiving host and transmit the alarm information.

Natural gas alarm: gas detector

Natural gas alarms generally detect their flammability, so catalytic combustion gas sensors are used for natural gas alarms. The working principle of catalytic combustion natural gas alarm is to use the resistance change of refractory metal platinum wire after heating to determine the concentration of combustible gases. When combustible gas enters the detector, it causes oxidation reaction (flameless combustion) on the surface of the platinum wire, and the heat generated increases the temperature of the platinum wire, causing a change in its electrical resistivity. Therefore, when encountering high temperature and other factors, the temperature of the platinum wire changes, and the electrical resistivity of the platinum wire changes, resulting in a change in the detected data.

Carbon monoxide detector: Carbon monoxide detector

The carbon monoxide gas alarm uses a carbon monoxide sensor to convert the concentration signal of carbon monoxide gas in the air into a weak current or internal pressure signal. After one or two stages of signal amplification, it is transmitted to the microcontroller for signal comparison and processing. If the capacitance exceeds the predetermined threshold, the microcontroller will emit an audible and visual alarm signal to drive the LED light, horn or buzzer.