[Tip] Analysis of the failure from the principle of flammable gas alarm

Flammable gas alarms are detectors installed in industrial and civil buildings that respond to single or multiple combustible gas concentrations. The most frequently used combustible gas alarms are catalytic flammable gas alarms and semi-conductor flammable gas alarms. The use of gas, natural gas, and liquefied gas in hotels, guesthouses, and family production rooms mainly uses semiconductor-type flammable gas alarms, and catalytic flammable gas alarms are mainly used in industrial sites that emit combustible gases and flammable vapors.

Catalytic flammable gas alarms measure the concentration of combustible gas using the change in resistance after the refractory metal platinum wire is heated. When the flammable gas enters the detector, an oxidation reaction (flaming combustion) occurs on the surface of the platinum wire. The heat generated by the oxidizing gas causes the temperature of the platinum wire to increase, and the resistivity of the platinum wire changes, so when high temperatures are encountered, etc. When the temperature of the platinum wire changes, the resistivity of the platinum wire changes, and the detected data also changes.

Semiconductor type combustible gas alarms measure the combustible gas concentration using semiconductor surface resistance changes. Semiconductor gas combustible gas detector with high sensitivity of the gas-sensitive semiconductor components, it encountered a combustible gas in the working state, the semiconductor resistance decreased, the decline in the concentration of flammable gas and a corresponding relationship.

Combustible gas alarm consists of detection and detection of two parts, with detection and detection capabilities. The principle of combustible gas alarm detection part is that the sensor of the instrument adopts a detection element, a fixed resistance and a zero adjustment potentiometer to form a detection bridge. The bridge uses a platinum wire as the carrier to catalyze the element. After the power is applied, the temperature of the platinum wire rises to the working temperature, and the air reaches the surface of the element by natural diffusion or other means. When there is no flammable gas in the air, the bridge output is zero. When the flammable gas is contained in the air and diffused on the detection element, flameless combustion occurs due to catalysis, so that the temperature of the detection element is increased and the resistance of the platinum wire is increased. The bridge circuit is out of balance and there is a voltage signal output. This voltage is proportional to the concentration of flammable gas. The signal is amplified and converted by analog to digital. The concentration of flammable gas is shown through the liquid display.

The principle of the detection part is that when the measured flammable gas concentration exceeds the limit value, the amplified bridge output voltage and circuit detection set voltage, through the voltage comparator, a square wave generator outputs a square wave signal to control the sound, In the light detection circuit, a continuous sound occurs in the buzzer, and the light emitting diode emits a bright signal, which emits a detection signal. From the principle of flammable gas alarms, we can see that if electromagnetic interference will affect the detection signal, data deviation will occur; if there is a collision or vibration, it will cause the device to break and the current detection failure will occur; if the environment is too humid or the equipment enters water, it may also cause A short circuit occurs in the flammable gas alarm, or the line resistance value changes, and a detection failure occurs.