some different types of gas sensors

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.

Types of Gas Sensors

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.

Characteristics of Gas Sensors

Stability

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

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.

Cross Sensitivity

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

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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