PPE

analyze the cause of failure from the principle of combustible gas alarm

Combustible gas alarm is a detector installed in industrial and civil buildings, which responds to single or multiple combustible gas concentrations. The most commonly used combustible gas alarms are catalytic combustible gas alarm and semi conductive combustible gas alarm. Semi conductive combustible gas alarm is mainly used in restaurants, hotels, family production rooms and other places where gas, natural gas and liquefied gas are used, and catalytic combustible gas alarm is mainly used in industrial places where combustible gas and combustible steam are emitted

the catalytic combustible gas alarm uses the resistance change of refractory metal platinum wire after heating to measure the concentration of combustible gas. When combustible gas enters the detector, it will cause oxidation reaction (flameless combustion) on the surface of platinum wire. The heat generated will increase the temperature of platinum wire, and the resistivity of platinum wire will change. Therefore, when encountering high temperature and other factors, the temperature of platinum wire will change, the resistivity of platinum wire will change, and the detection data will also change

the semiconducting combustible gas alarm uses the change of semiconductor surface resistance to measure the concentration of combustible gas. Semiconductor combustible gas alarm uses gas sensitive semiconductor element with high sensitivity. When it meets combustible gas in working state, semiconductor resistance decreases, and the decrease value has corresponding relationship with combustible gas concentration

combustible gas alarm is composed of detection and detection, with detection and detection functions. The principle of combustible gas alarm detection part is that the sensor of the instrument uses detection elements, fixed resistance and zero potentiometer to form a detection bridge. The bridge uses platinum wire as carrier to catalyze the element. After power on, the platinum wire temperature rises to the working temperature, and the air reaches the element surface by natural diffusion or other ways. When there is no combustible gas in the air, the output of the bridge circuit is zero. When there is combustible gas in the air and diffuses to the detection element, flameless combustion occurs due to catalytic action, which increases the temperature of the detection element, increases the resistance of the platinum wire, and makes the bridge circuit out of balance. As a result, a voltage signal is output. The voltage is proportional to the concentration of combustible gas, and the signal is amplified, Analog to digital conversion, through the liquid display shows the concentration of combustible gas

the principle of the detection part is that when the combustible gas concentration exceeds the limit value, the amplified bridge output voltage and the circuit detection set voltage are used to output a group of square wave signals through the voltage comparator and square wave generator to control the sound and light detection circuit, the buzzer generates continuous sound, and the LED flashes to send out the detection signal. From the principle of combustible gas alarm, it can be seen that if there is electromagnetic interference, the detection signal will be affected and data deviation will occur; 1f there is a collision, vibration, resulting in open circuit equipment, detection failure will be present; 1f the environment is too humid or the equipment is flooded, it may also cause the combustible gas alarm to have a short circuit, or the line resistance value changes, resulting in detection failure

Back to list