Definition
A combustible gas detector is a safety monitoring device used to detect the concentration of combustible gases in the environment. It measures gas concentrations in real time and alerts when preset alarm thresholds are reached to prevent fire or explosion accidents. This type of instrument is widely used in industrial and civil places with the risk of combustible gas leakage, and is one of the important technical means to ensure the safety of life and property.
Principle
The core working principle of a flammable gas detector is based on sensor technology. Common working principles include catalytic combustion and infrared absorption. The catalytic combustion sensor uses the Wheatstone bridge structure, in which the detection element coated with catalyst undergoes flameless combustion when it comes into contact with combustible gas, causing the temperature and resistance of the element to change, resulting in the output of an electrical signal proportional to the gas concentration of the bridge, and its basic relationship can be expressed as:ΔV ∝ C, where ΔV is the output voltage change, and C is the gas concentration. The infrared absorption sensor is based on the selective absorption of infrared light at a specific wavelength by gas molecules, and according to Lambert-Beale's law, the gas concentration is estimated by measuring the attenuation of light intensity, and the relationship is:I = I0 e-kCL, where I is the intensity of transmitted light, I0is the incident light intensity, k is the absorption coefficient, C is the gas concentration, and L is the path length.
Measurement method
According to the sampling method, the measurement method can be divided into diffusion type and pump suction type. The diffusion type relies on the natural diffusion of gas to the sensor and is suitable for continuous monitoring of fixed points. The pump suction type actively extracts gas samples through the built-in pump and feeds them into the detection chamber, which is suitable for occasions where remote sampling or detection of hard-to-reach areas are required. Instruments typically use quantitative measurements to display concentrations as a percentage of the lower explosion limit. Calibration is a critical step in ensuring accurate measurements, and regular zero point and range calibration with standard gases is required.
Influencing factors
The measurement performance of the instrument is affected by a variety of environmental and operational factors. Changes in ambient temperature and humidity may affect sensor sensitivity and response time. The presence of substances such as silicides, sulfides, or leadides can cause sensor poisoning or inhibition. Changes in air pressure affect the rate of gas diffusion and sensor readings. Cross-interference from different gases can also cause reading bias. In addition, sensors experience natural aging, and their sensitivity gradually decreases over time, which needs to be compensated for by regular maintenance and calibration.
Application:
Flammable gas detectors perform safety monitoring functions in many fields. In the petrochemical industry, it is used to monitor hydrocarbon gas leaks in production plants, tank farms and pipeline valves. In gas supply systems, natural gas or liquefied petroleum gas is monitored in places such as pressure regulating stations, kitchens, etc. Underground in coal mines, methane accumulation is monitored. Monitor solvent vapor concentrations in coating operations, laboratories, and semiconductor manufacturing environments. These applications help to achieve early warning and provide a basis for control measures such as ventilation and air supply cut-off.
Selection
The selection process needs to take into account the testing needs and environmental conditions. First, the target gas type and its lower explosion limit should be clarified, and the instrument corresponding to the range and sensitivity should be selected. According to the level of potential hazardous areas in the installation environment, determine the explosion-proof level and protection standards required by the instrument. In the presence of multiple interfering gases, the selectivity of the sensor needs to be evaluated. Fixed-mounted instruments are usually used for long-term continuous monitoring, while inspection and emergency testing are suitable for portable equipment. In addition, factors such as the instrument's response time, alarm style, data recording function, and maintenance convenience need to be considered to ensure that the selected instrument matches the specific application scenario.