Proper Operating Steps and Maintenance for Combustible Gas Detectors
① Combustible gas detectors are installed in industrial and civil buildings to respond to the concentration of one or multiple types of combustible gases. The two most widely used types in practical applications are catalytic combustible gas detectors and semiconductor combustible gas detectors. Semiconductor detectors are mainly applied in restaurants, hotels, domestic kitchens and other sites that consume coal gas, natural gas and liquefied petroleum gas, while catalytic detectors are predominantly used in industrial locations where combustible gases and vapors are released.
② A catalytic combustible gas detector measures combustible gas concentration based on the resistance change of heated refractory platinum wire. When combustible gas enters the detector, an oxidation reaction (flameless combustion) occurs on the surface of the platinum wire. The generated heat raises the temperature of the platinum wire and changes its resistivity. Similarly, high ambient temperature and other external factors will also alter the resistivity of the platinum wire and lead to inaccurate detection readings.
③ A semiconductor combustible gas detector calculates gas concentration by detecting the surface resistance variation of semiconductor materials. It adopts highly sensitive gas-sensitive semiconductor components. Under operating condition, the resistance of the semiconductor decreases when exposed to combustible gas, and the degree of resistance reduction has a corresponding proportional relationship with the concentration of the combustible gas.
④ A combustible gas detector consists of a measurement unit and an alarm unit with corresponding functions. Working principle of the measurement unit: The sensor forms a measuring bridge circuit composed of the sensing element, fixed resistors and zero-adjustment potentiometer. The bridge takes platinum wire as the carrier of the catalytic component. After power is supplied, the platinum wire heats up to its operating temperature, and ambient air reaches the surface of the component through natural diffusion or other sampling methods. When there is no combustible gas in the air, the bridge outputs zero voltage. If combustible gas diffuses to the sensing component, flameless combustion takes place due to catalytic reaction, which increases the temperature of the sensing element and the resistance of the platinum wire. This unbalances the bridge and outputs a voltage signal proportional to the gas concentration. The signal is amplified and converted via analog-to-digital conversion, and the concentration value is finally displayed on the liquid crystal screen.
Working principle of the alarm unit: When the detected combustible gas concentration exceeds the threshold, the amplified output voltage of the bridge is compared with the preset reference voltage by a voltage comparator. A square wave generator then outputs square wave pulses to drive the audible and visual alarm circuit. The buzzer emits continuous sound and the light-emitting diode flashes to trigger the alarm.
It can be concluded from the working principle that electromagnetic interference will interfere with detection signals and cause data deviation; impact or vibration may result in open circuits and detection failure; excessive humidity or water ingress inside the device can lead to short circuits or changes in circuit resistance, thus triggering detection faults.
Combustible gas detectors are calibrated and manufactured according to the specific gases to be monitored on site. They can respond to the concentration of single or multiple combustible gases. Such detectors are required for all premises where flammable and explosive gases may exist.
