Definition
A combustible gas monitor is a safety device used to detect the concentration of combustible gases in the environment and issue early warnings. Its core function is real-time monitoring, when the gas concentration reaches the preset alarm threshold, the instrument will prompt the risk through sound and light signals to prevent fire or explosion accidents. Such instruments are widely used in industrial and civil places where there is a risk of combustible gas leakage, and are an important technical means to ensure the safety of life and property.
Principle
The core of the combustible gas monitor is the sensor, which is mainly based on two mainstream technologies: catalytic combustion and infrared absorption. The catalytic combustion sensor uses the Wheatstone bridge principle, in which the detection element coated with a catalyst occurs flameless combustion when it comes into contact with combustible gas, resulting in an increase in the temperature of the element and a change in resistance, thereby breaking the bridge balance and generating an electrical signal proportional to the gas concentration. The output signal ΔV can be approximately expressed as:
ΔV ∝ (Rcat - Rref) · I
where RcatTo detect the resistance of the component, RrefTo compensate for the resistance of the component, I is the bridge current. The infrared absorption sensor calculates the gas concentration based on the absorption characteristics of the gas to a specific wavelength of infrared light, and uses the Lambert-Beale law to calculate the gas concentration by measuring the attenuation degree of infrared light after passing through the measured gas, and the relationship can be expressed as:
I = I0 · e-αCL
Equation I0is the incident light intensity, I is the transmitted light intensity, α is the absorption coefficient, C is the gas concentration, and L is the optical path length.
Measurement method
According to the sampling method, the measurement can be divided into diffusion type and pump suction type. The diffusion type relies on natural gas diffusion contact sensors for continuous monitoring of fixed points, easy to install and low maintenance requirements. The pump suction type actively extracts gas samples through the built-in pump and feeds them into the sensor chamber, which is suitable for remote sampling, pipeline detection, or environments where gas is not easy to spread. In operation, instruments usually use quantitative measurement, showing concentration as a percentage of the lower explosion limit. Daily calibration is a key part of ensuring measurement accuracy, and it is necessary to regularly calibrate the zero point and range with standard concentrations of gas.
Influencing factors
The measurement performance of a monitor is affected by a variety of environmental and operational factors. Significant changes in ambient temperature and humidity can affect sensor sensitivity and response speed, and some sensors may experience reading drift in high humidity environments. The presence of hydrogen sulfide, silicide and other substances in the background gas may cause poisoning or inhibition of catalytic combustion sensors, resulting in permanent performance degradation. Changes in air pressure can also affect the rate of gas diffusion and sensor readings. In addition, the natural aging of the sensor, dust clogging, and electromagnetic interference are also factors that need to be considered in practical applications. Therefore, proper installation location, regular maintenance and calibration are essential for maintaining long-term instrument reliability.
Applications
The application of combustible gas monitors is found in numerous industries where there is a risk of combustible gases. In the field of petrochemical and natural gas transmission and distribution, it is used to monitor the leakage of methane, propane, hydrogen and other gases around pipelines, storage tanks, reactors and plants. In the field of municipal gas, it is installed in pressure regulating stations, boiler rooms, catering kitchens and other places to monitor natural gas or liquefied petroleum gas. In addition, such instruments need to be deployed in enclosed or semi-enclosed spaces such as ship cabins, spraying workshops, lithium battery production workshops, landfills, and underground pipe galleries to prevent the risk of gas accumulation. Its deployment is an important part of process safety and occupational health protection.
Selection considerations
Selection is a comprehensive evaluation process based on specific application scenarios and needs. The first step is to identify the type of gas to be measured and its lower explosion limit, among other characteristics, to determine the appropriate sensor type. Secondly, it is necessary to evaluate the monitoring environment, including the level of potential hazardous areas, temperature range, humidity level, and the presence of interfering gases, and select instruments that meet the corresponding protection level and environmental adaptability. The choice of sampling method depends on whether the monitoring point is stationary or requires mobile inspection. The instrument's response time, detection resolution, adjustable range of alarm setpoints, and data logging and output capabilities are also technical parameters to be compared. Finally, compliance with regulations and standards, stability over time, and ease of maintenance and calibration are also considered. Through systematic evaluation, monitoring equipment can be selected that matches specific safety requirements.