Fault Generation Analysis Based on the Working Principle of Combustible Gas Detectors
① Combustible gas detectors are installed in industrial and civil buildings to respond to the concentrations of single or multiple combustible gases. Catalytic and semiconductor types are the two most commonly used in routine applications.
Semiconductor combustible gas detectors are mainly deployed in restaurants, hotels, domestic kitchens and other premises using coal gas, natural gas or liquefied petroleum gas. Catalytic combustible gas detectors are primarily used in industrial sites where combustible gases or vapors are released.
② The catalytic type measures combustible gas concentration by means of resistance variation of a heated refractory platinum wire. When combustible gas enters the detector, an oxidation reaction (flameless combustion) occurs on the surface of the platinum wire. The heat generated raises the temperature of the platinum wire and changes its resistivity. Therefore, factors such as high ambient temperature will alter the temperature and resistivity of the platinum wire and lead to deviations in measured data.
③ The semiconductor type determines combustible gas concentration based on changes in the surface resistance of semiconductors. Semiconductor combustible gas detectors adopt highly sensitive gas‑sensing semiconductor elements. During operation, the resistance of the semiconductor decreases upon exposure to combustible gas, and the magnitude of resistance reduction correlates with the combustible gas concentration.
④ A combustible gas detector consists of a detection unit and an alarm unit, with both measurement and alarm functions. For the detection unit, the sensor's detecting element, fixed resistors and zero‑adjustment potentiometer form a detection bridge circuit.
The bridge adopts a platinum‑wire catalytic carrier element. When powered on, the platinum wire heats up to its operating temperature, and air reaches the element surface via natural diffusion or other approaches. In the absence of combustible gas in the air, the bridge output is zero. When combustible gas diffuses onto the detecting element, flameless combustion occurs due to catalysis, which raises the element temperature and increases the resistance of the platinum wire. This unbalances the bridge and produces a voltage signal proportional to the combustible gas concentration. After amplification and analog‑to‑digital conversion, the concentration of combustible gas is displayed on the liquid‑crystal screen.
As for the alarm unit: when the measured combustible gas concentration exceeds the threshold, the amplified bridge output voltage is compared with the preset alarm voltage through a voltage comparator. A square‑wave generator then outputs square‑wave signals to control the audible and visual alarm circuits. The buzzer emits a continuous tone and the light‑emitting diode flashes to send out an alarm signal.
It can be seen from the working principle of combustible gas detectors that electromagnetic interference will affect detected signals and cause data deviation; collisions and vibration that result in an open circuit may lead to detection failure; excessive ambient humidity or water ingress into the device may trigger a short circuit or change the resistance of circuits, thus causing detection faults.
