Common gas sensing technology and comparison
1.1 Semiconductor Gas Sensor
High sensitivity at low concentrations
PPM Level
Oxygen molecules will capture free electrons in the material, thereby reducing the conductivity of special semiconductor materials; if methane is present in the air, methane as a reducing gas will react with oxygen molecules, thereby reducing the ability of oxygen molecules to capture free electrons. The number of free electrons increases, and the conductivity rises.
5%VOL = 50000PPM = 100%LEL —— FOR METHANE GAS
1.2 Catalytic Sensor
Excellent output linearity
Does not react with non-flammable gases
LEL Level
Under the action of the catalyst on the platinum wire, the combustible gas below the explosion limit will be decomposed on the surface of the catalyst. The temperature rise will change the resistance of the platinum wire, and the concentration of combustible gas in the air can be detected by detecting the change of resistance.
1.3 Thermal Transfer Sensor
Suitable for high concentration detection
VOL Level
The thermal conductivity of gas containing methane is different from that of air. Two types of airflows are used to blow the heated platinum wire separately. The difference in methane concentration is reflected in the cooling capacity of the airflow, resulting in a change in the resistance of the platinum wire. The resistance is measured to obtain the methane concentration.
1.4 NDIR（Non-Dispersive Infrared）Sensor
Anti-poisoning
Long-term stability
Wide temperature range detection
The combination of a broad-spectrum light source and a color filter is used to generate infrared radiation in a specific wavelength range. The light penetrates the gas to be measured and reaches the infrared detector. The methane molecules absorb this infrared light and detect the change in light intensity to obtain the concentration level.
1.5 Laser Gas Sensor
Unique Selectivity
PPM / PPB Level
0 - 100%VOL
Response time - Millisecond
Achieve telemetry
Physical detection, can penetrate glass
The laser methane telemeter is a gas detection device for remote measurement of methane gas. The device emits two laser beams, a visible indicating laser is directed to the detection area (red or green), and an invisible infrared laser is used to measure the methane gas present at a long distance and is expressed in unit concentration (ppm.m).
“Methane molecules absorb light at specific wavelengths.”
—— Molecular absorption spectroscopy principle
“There is a linear relationship between the concentration and the absorbance of the solution, which enables the concentration of a solution to be calculated by measuring its absorbance.”
—— Lambert-Beer law
As to methane, the absorption line in the spectrum is distributed as this chart and we are using laser with the wavelength in 1653 nanometer. This absorption line is only effective for methane gas which is not affected by other species like water vapor, carbon dioxide or any other gas components in the atmosphere.
1.6 Features of different sensing technologies and products
Different sensor technology characteristics determine the scope of use of the product:
In traditional gas sensor products - semiconductors, catalytic combustion, and heat conduction together - constitute the low, medium, and high full range coverage from PPM, LEL to VOL devices. NDIR technology has a wider range and faster speed than traditional sensing technology. What more, laser sensors can cover a wide range from ppm to VOL, with the fastest response speed.
According to the different detection limits and response speed of the instrument, different products are suitable for different detection environments and the products complement each other.
