Analysis of Fault Generation from the Principle of Combustible Gas Detectors
① Combustible gas detectors are installed in industrial and civil buildings to respond to the concentration of single or multiple combustible gases. Catalytic and semiconductor types are the two most commonly used in daily applications.
Semiconductor combustible gas detectors are mainly adopted in restaurants, hotels, domestic kitchens and other sites using coal gas, natural gas or liquefied petroleum gas. Catalytic combustible gas detectors are primarily used in industrial locations where combustible gases or vapors are released.
② The catalytic type measures combustible gas concentration based on resistance changes of a heated refractory platinum wire. When combustible gas enters the detector, an oxidation reaction (flameless combustion) occurs on the platinum wire surface. The heat generated raises the platinum wire temperature and changes its resistivity. Accordingly, factors such as high ambient temperature will alter the platinum wire temperature and resistivity, leading to deviations in measured readings.
③ The semiconductor type determines combustible gas concentration by detecting surface resistance variations of semiconductor materials. Semiconductor combustible gas detectors adopt highly sensitive gas‑sensing semiconductor elements. During operation, the resistance of the semiconductor drops upon contact with combustible gas, and the magnitude of resistance reduction corresponds to the combustible gas concentration.
④ A combustible gas detector consists of a measurement unit and an alarm unit, featuring both detection and alarm functions. For the measurement unit, the sensor's detecting element, fixed resistors and zero‑adjustment potentiometer form a Wheatstone bridge circuit.
The bridge uses a platinum‑wire catalytic bead element. When powered on, the platinum wire heats up to its operating temperature. Air reaches the element surface via natural diffusion or other means. In the absence of combustible gas, the bridge outputs zero. When combustible gas diffuses onto the sensing element, flameless combustion takes place due to catalysis, raising the element temperature and increasing platinum wire resistance. This unbalances the bridge and generates a voltage signal proportional to the combustible gas concentration. After amplification and analog‑to‑digital conversion, the concentration value is displayed on the liquid‑crystal screen.
For the alarm unit: when the measured combustible gas concentration exceeds the preset threshold, the amplified bridge output voltage is compared with the preset alarm voltage via a voltage comparator. A square‑wave generator then outputs square‑wave signals to drive the audible and visual alarm circuits. The buzzer emits a continuous tone and the LED flashes to trigger the alarm.
It can be concluded from the working principle of combustible gas detectors that electromagnetic interference will distort measurement signals and cause reading errors; collisions or vibration may create open circuits and result in detection failure; excessive humidity or water ingress may lead to short circuits or changes in circuit resistance, triggering detector faults.
