Principle Analysis of Faults of Combustible Gas Detectors
1. Combustible gas detectors installed and used in industrial and civil buildings are detectors that respond to the concentration of a single or multiple combustible gases. The most commonly used combustible gas detectors in daily life are two types: catalytic combustible gas detectors and semiconductor combustible gas detectors. Places such as restaurants, hotels, and home kitchens that use coal gas, natural gas, or liquefied petroleum gas mainly use semiconductor combustible gas detectors, while industrial places where combustible gases and combustible vapors are emitted mainly use catalytic combustible gas detectors.
2. Catalytic combustible gas detectors measure the concentration of combustible gases by utilizing the change in resistance of a refractory metal platinum wire after heating. When a 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 the resistivity of the platinum wire changes. Therefore, when exposed to factors such as high temperature, the temperature of the platinum wire changes, its resistivity changes, and the detected data also changes.
3. Semiconductor combustible gas detectors measure the concentration of combustible gases by utilizing the change in the surface resistance of the semiconductor. Semiconductor combustible gas detectors use gas-sensitive semiconductor elements with relatively high sensitivity. When in the working state and encountering a combustible gas, the resistance of the semiconductor decreases, and the decrease value has a corresponding relationship with the concentration of the combustible gas.
4. A combustible gas detector consists of two parts: the detection part and the alarm part, and it has both detection and alarm functions. The principle of the detection part of the combustible gas detector is that the sensor of the instrument uses a detection element, a fixed resistor, and a zero-adjusting potentiometer to form a detection bridge circuit. The bridge circuit uses a platinum wire as the carrier catalytic element. After being powered on, the temperature of the platinum wire rises to the operating temperature, and air reaches the surface of the element by natural diffusion or other means. When there is no combustible gas in the air, the output of the bridge circuit is zero. When there is a combustible gas in the air and it diffuses to the detection element, due to the catalytic effect, flameless combustion occurs, causing the temperature of the detection element to rise and the resistance of the platinum wire to increase, making the bridge circuit out of balance. Thus, a voltage signal is output. The magnitude of this voltage is proportional to the concentration of the combustible gas. After the signal is amplified and subjected to analog-to-digital conversion, the concentration of the combustible gas is displayed on the liquid display. The principle of the alarm part is that when the concentration of the measured combustible gas exceeds the limit value, the amplified output voltage of the bridge circuit and the set voltage of the alarm circuit, through the voltage comparator, the square wave generator outputs a set of square wave signals to control the sound and light alarm circuit. The buzzer emits a continuous sound, and the light-emitting diode flashes to send out an alarm signal. From the principle of the combustible gas detector, it can be seen that if there is electromagnetic interference, it will affect the detected signal and cause data deviation; if there is a collision or vibration, resulting in a circuit break of the device, the detection will fail; if the environment is too humid or the device gets water inside, it may also cause a short circuit in the combustible gas detector or a change in the resistance value of the circuit, leading to detection failures.
