Detailed explanation of the use and maintenance of laboratory combustible gas detectors

　　1. Combustible gas detectors are detectors installed and used in industrial and civil buildings that respond to the concentration of single or multiple combustible gases. The most commonly used combustible gas detectors are catalytic combustible gas detectors and semiconductor combustible gas detectors. Semiconductor combustible gas detectors are mainly used in restaurants, hotels, home workshops and other places that use coal gas, natural gas, and liquefied gas, while catalytic combustible gas detectors are mainly used in industrial places that emit combustible gases and combustible vapors.

　　2. Catalytic flammable gas detectors use the resistance change of refractory metal platinum wire after heating to measure the concentration of combustible gas. When the combustible gas enters the detector, it causes an oxidation reaction (flameless combustion) on the surface of the platinum wire. The heat generated by the reaction raises the temperature of the platinum wire, and the resistivity of the platinum wire changes. Therefore, when encountering factors such as high temperature, the temperature of the platinum wire changes, and the resistivity of the platinum wire changes, and the detected data will also change.

　　3. Semiconductor-type flammable gas detectors use the change in semiconductor surface resistance to measure the concentration of flammable gas. Semiconductor flammable gas detectors use highly sensitive gas-sensitive semiconductor elements. When they encounter flammable gas in the working state, the semiconductor resistance decreases, and the decrease value corresponds to the concentration of flammable gas.

　　4. The combustible gas detector consists of two parts: detection and detection, and has detection and detection 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 zeroing potentiometer to form a detection bridge. The bridge uses platinum wire as a carrier catalytic element. After power is turned on, the temperature of the platinum wire rises to the working temperature, and the 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 is zero. When the air contains combustible gas and diffuses to the detection element, flameless combustion occurs due to catalysis, which increases the temperature of the detection element, increases the resistance of the platinum wire, and causes the bridge to lose balance, thereby outputting a voltage signal. The magnitude of this voltage is proportional to the concentration of the combustible gas. The signal is amplified and converted to analog to digital, and the concentration of the combustible gas is displayed through a liquid display. The principle of the detection part is that when the concentration of the combustible gas being measured exceeds the limit value, the output voltage of the amplified bridge circuit is compared with the circuit detection set voltage, and a set of square wave signals are output through the voltage comparator and the square wave generator to control the sound and light detection circuits, the buzzer makes continuous sounds, the light-emitting diode flashes, and sends out a detection signal. From the principle of the combustible gas detector, it can be seen that if electromagnetic interference occurs, it will affect the detected signal and cause data deviation; if there is a collision or vibration that causes the equipment to be disconnected, the detection will fail; if the environment is too humid or the equipment is flooded, it may also cause the combustible gas detector to short-circuit, or the line resistance value may change, resulting in a detection failure.

　　2. Failure analysis and countermeasures of users using combustible gas detectors

　　1. Improper use by users

　　When the user uses the detector, the air conditioner and heating equipment are installed close to the combustible gas detector. When the air conditioner and heating equipment are used, if the cold and warm air flows directly through the combustible gas alarm, it may cause the resistivity of the platinum wire of the combustible gas alarm to change and cause errors. Therefore, the combustible gas alarm should be kept away from the air conditioner and heating equipment to avoid malfunctions caused by improper installation. Users should also pay attention to electromagnetic interference when using the combustible gas detector. The installation position, installation angle, protective measures and system wiring of the combustible gas alarm should be prevented from electromagnetic interference. There are three main ways in which the electromagnetic environment affects the combustible gas alarm: electromagnetic wave interference in the air, narrow pulse groups on the power supply and other input and output lines, and human static electricity. For example: when the combustible gas alarm is installed close to the air conditioner, it will cause the system's detection to deviate; if the detection line is close to the power line, lighting line and other strong power lines, and no anti-electromagnetic interference measures are added, the system will also produce detection deviations. When using the combustible gas detector, users should pay attention to factors that are prone to cause malfunctions, such as dust, high temperature, humidity, rain, etc. When an exhaust fan is required to be installed in the place where a combustible gas alarm is installed, if the exhaust fan is installed adjacent to the combustible gas detector, the leaked combustible gas will not be able to fully diffuse to the vicinity of the combustible gas alarm, resulting in failure to detect in time and missed opportunities. In addition, users should also pay attention to the installation of combustible gas detectors in explosion-proof places. For example, Class A factories that emit combustible gases should use explosion-proof combustible gas alarms, and their explosion-proof levels should not be lower than the corresponding explosion-proof level requirements of the current specifications. Users using combustible gas detectors should also pay attention to avoid places where high temperature, high humidity, steam, and oil smoke can reach. Do not place or hang objects on the detector. The installed combustible gas detector cannot be moved arbitrarily. When using combustible gas alarms, users should try to use products with replaceable sensor probes for ease of use.

　　(II) Irregular construction process

　　Irregular construction process will cause the combustible gas detector to detect faults during use. If the combustible gas detector is not located near the equipment where combustible gas is easy to leak, or is installed adjacent to the exhaust fan during installation, the leaked combustible gas cannot be fully diffused to the vicinity of the combustible gas detector, so that the leakage risk cannot be detected by the combustible gas detector in time. For residential combustible gas detectors, they should be installed near the gas pipelines and stoves in the kitchen. When residents use natural gas, the gas detector is installed within 300mm from the ceiling; when residents use liquefied petroleum gas, the gas detector should be installed within 300mm from the ground. If the combustible gas detector is not reliably grounded, electromagnetic interference cannot be eliminated, which will inevitably affect the voltage and cause inaccurate detection data. Therefore, the combustible gas detector should be reliably grounded during construction. The combustible gas detector and the wiring terminals are located in places that are prone to collision or water ingress, causing the electrical circuit to be broken or short-circuited. Welding must use non-corrosive flux, otherwise the joints will corrode and become detached or the line resistance will increase, affecting normal detection. Do not drop or throw the detector to the ground. After construction, debugging should be carried out to ensure that the combustible gas alarm is in normal working condition.

　　(III) Maintenance

　　In order for a flammable gas detector to detect flammable gas information, the detector must communicate with the detection environment. Therefore, it is inevitable that various pollutants and dust in the environment enter the detector, which objectively damages the working conditions of the detector. The working environment of flammable gas detectors is relatively harsh, and many are installed outdoors. Poor maintenance will cause errors or no detection in the flammable gas alarm. Therefore, regular cleaning and maintenance of flammable gas detectors is an important task to prevent malfunctions.

　　Grounding should be checked regularly. If the grounding does not meet the standard requirements or is not grounded at all, the combustible gas detector will be susceptible to electromagnetic interference and cause failures. Prevent component aging. Considering reliability, practice has proved that the failures caused by component aging in systems with a service life of more than 10 years tend to increase. Therefore, if the service life exceeds the requirements of the use regulations, it should be replaced in time.