Flammable Gas Detectors ‑ Operation & Maintenance
① Combustible gas detectors are installed in industrial and civil buildings to respond to the concentration of single or multiple flammable gases. The two most commonly‑used types in daily applications are catalytic‑bead combustible gas detectors and semiconductor‑type combustible gas detectors. Semiconductor‑type detectors are mainly adopted in restaurants, hotels, domestic kitchens and other sites using coal gas, natural gas and liquefied petroleum gas. Catalytic‑bead combustible gas detectors are primarily used in industrial premises where flammable gases or vapors are released.
② A catalytic‑bead combustible gas detector measures flammable‑gas concentration based on resistance variation of a heated refractory platinum wire. When flammable gas enters the detector, an oxidation reaction (flameless combustion) takes place on the surface of the platinum wire. The generated heat raises the temperature of the platinum wire and changes its resistivity. Therefore, high‑temperature conditions will alter the platinum‑wire temperature and resistivity, which further leads to deviation in measured readings.
③ A semiconductor‑type combustible gas detector determines flammable‑gas concentration by detecting surface‑resistance changes of semiconductor materials. It adopts highly‑sensitive gas‑sensing semiconductor components. Under operating conditions, the resistance of the semiconductor drops upon contact with flammable gas, and the magnitude of resistance reduction corresponds to the concentration of flammable gas.
④ A combustible gas detector consists of a measuring unit and an alarm unit, featuring both detection and alarm functions. For the measuring unit: the sensor's detecting element, fixed resistor and zero‑adjustment potentiometer form a measuring bridge circuit. The bridge uses platinum‑wire‑based catalytic elements. After power‑on, the platinum wire rises to operating temperature, and air reaches the element surface via natural diffusion or other approaches. When no flammable gas exists in ambient air, the bridge outputs zero signal. If flammable gas diffuses onto the detecting element, flameless combustion occurs due to catalytic effect, raising the element temperature and platinum‑wire resistance, which unbalances the bridge and generates a voltage signal proportional to flammable‑gas concentration. After amplification and analog‑to‑digital conversion, the concentration value is displayed on the liquid‑crystal screen.
For the alarm unit: once the measured flammable‑gas concentration exceeds the threshold value, the amplified bridge‑output voltage is compared with the preset circuit voltage by a voltage comparator. A square‑wave generator outputs square‑wave signals to drive acoustic‑optical alarm circuits. The buzzer emits continuous sound and light‑emitting diodes flash to trigger alarm notifications.
As can be seen from the working principle, electromagnetic interference may distort detection signals and cause reading errors. Collision or vibration may trigger open‑circuit faults and result in alarm failure. Excessive humidity or water ingress may cause short‑circuit or line‑resistance variation and bring about detector malfunctions.
