Figure 1: A series of gas sensors.
The gas sensor is used to detect specific gases in a certain area and continuously measure the concentration of gases as well. In the areas of coal, petroleum, chemical, municipal, medical, transportation, family and other safety protection, gas sensors are often used to detect the concentration or presence of gases that are flammable, toxic, or their oxygen consumption. Gas sensors are often indispensable in safety systems thanks to the detection of gases around.
From perspectives of the working principle, characteristics, and measuring technology, as well as materials, manufacturing process, the test object, and the field of application, there could constitute different classification standards, deriving complexity of classification systems. It has been especially united on the issue of classification standards, so it is hard to carry on the strict system.
Detected gas Features |
Types |
||||
Combustible gas sensor |
Catalytic combustion type |
Infrared |
Thermal conductivity |
Semiconductor type |
|
Toxic gas sensor |
Electro-chemical |
Metal semiconductor body |
Light ionization |
Flame ionization type |
|
Harmful gas sensor |
Infrared |
||||
Oxygen sensor |
Paramagnetic type |
Zirconia type |
Table 1: Four types of gas sensors divided by features of the detected gas.
Ways to obtain gases |
Definition |
Diffusion type sensor |
The sensor directly contacts the measured gas through natural diffusion. |
Inhalation gas sensor |
The gas is introduced into the sensor detection element by using the getter pump and other devices. According to the dilute strength of the measured gas, there are full-inhalation type and dilution type. |
Table 2: Definitions of diffusion type sensor and inhalation gas sensor.
Gas composition |
Use |
Single gas sensor |
For specific gases. |
Compound gas sensor |
Simultaneous detection of various gas components. |
Table 3: Single gas sensor and compound gas sensor as well as their uses.
Detection principle |
Thermal sensor |
Electro-chemical sensor |
Magnetic gas sensor |
Optical gas sensor |
Semiconductor gas sensor |
Gas chromatography sensor |
Table 4: Six types of gas sensors divided by the detection principle.
In addition, gas sensors are also divided into portable gas sensors and fixed gas sensors according to the use methods.
The stability of the basic response of the sensor during the whole working time depends on the zero drift and interval drift. Zero drift refers to the change of output response of the sensor when there is no target gas. And interval drift refers to the response change when the sensor is continuously placed in the target gas, which is represented by the decrease of the output signal of the sensor. In ideal conditions, the occurrence rate of the zero drift is less than 10% per year under continuous operation of the sensor.
Sensitivity is the ratio of the change in the output to the change in the measured input of the sensor. It depends on the technology used in the sensor’s structure. Most types of gas sensors are designed based on biochemical, electro-chemical, physical, and optical principles. The first thing is to select a sensitive technology that is sensitive enough to the valve limit or the detection of the percentage of the lowest explosion limit for the target gas.
This can be determined by measuring the sensor response generated by a particular concentration of interfering gas. And the response is equivalent to the sensor response generated by a given concentration of the target gas. This property is important in tracking multiple gases because. An ideal sensor should have high sensitivity and selectivity.
Corrosion resistance is the ability to be exposed to target gases with large volume. In case of severe gas leakage, the probe should be able to withstand 10~20 times the desired gas volume fraction. Sensor drift and zero correction should be as small as possible after returning to normal operating conditions. The basic characteristics of gas sensors are the sensitivity, selectivity and stability, which are mainly determined through sensors’ materials. The selection of appropriate materials and the development of new materials can optimize the sensitivity of gas sensors.
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