Fault Generation Analysis from the Perspective of Combustible Gas Detector Principle
① Flammable gas detectors are installed in industrial and civil buildings to respond to the concentration of single or multiple combustible gases. The two most commonly used types in daily applications are catalytic bead flammable gas detectors and semiconductor flammable gas detectors. Semiconductor detectors are mainly adopted in restaurants, hotels, household kitchens and other premises using coal gas, natural gas and liquefied petroleum gas. Catalytic bead detectors are widely deployed in industrial sites where flammable gases and vapors are released.
② The catalytic bead flammable gas detector measures gas concentration based on the resistance change of heated refractory platinum wire. When flammable gas enters the detector, an oxidation reaction (flameless combustion) occurs on the platinum wire surface. The generated heat raises the temperature of the platinum wire and alters its resistivity. Therefore, external factors such as high ambient temperature will change the platinum wire temperature and resistivity, leading to deviation in measured readings.
③ The semiconductor flammable gas detector determines gas concentration according to the surface resistance variation of semiconductor materials. It adopts highly sensitive gas-sensitive semiconductor components. Under operating conditions, the resistance of the semiconductor drops upon contact with flammable gas, and the resistance drop is proportional to the gas concentration.
④ A flammable gas detector consists of a measuring module and an alarm triggering module with corresponding functional units. Working principle of the measuring module: The sensor forms a measuring bridge circuit composed of sensing elements, fixed resistors and a zero-adjustment potentiometer. The bridge uses platinum wire as the carrier for catalytic components. After power-on, the platinum wire heats up to its working temperature, and ambient air reaches the component surface via natural diffusion or other sampling methods. When no flammable gas exists in the air, the bridge outputs zero voltage. If flammable gas diffuses onto the sensing element, flameless catalytic combustion takes place, elevating the component temperature and increasing the platinum wire resistance. This unbalances the bridge and generates an output voltage proportional to the flammable gas concentration. The voltage signal is amplified, converted from analog to digital, and the gas concentration value is displayed on the liquid crystal screen.
Working principle of the alarm triggering module: When the measured flammable gas concentration exceeds the threshold, the amplified bridge output voltage is compared with the preset reference voltage through a voltage comparator. A square wave generator then outputs square wave pulses to drive the sound and light alarm circuit. The buzzer emits continuous audible alerts and light-emitting diodes flash to send out warning signals.
It can be concluded from the working principle that electromagnetic interference will distort detection signals and cause reading errors; collisions and vibrations may cause open circuits and complete detection failure; excessive ambient humidity or water ingress into the device can result in short circuits or changes in circuit resistance, ultimately triggering detection malfunctions.
