Gas Detector


Gas Sensors Types, Working Principles, Application

Gas Sensors Types, Working Principles, Application

A gas sensor detects a specific gas and measures whether the gas is present near the sensor, or its content in the air. Therefore, gas sensors are often indispensable in safety systems. The gas sensor has many different types and can measure different gases. There are sensors that measure non-toxic gases such as oxygen and carbon dioxide, and sensors that detect toxic gases such as carbon monoxide, TVOC, and ammonia. Gas sensors are often used in flammable, explosive and toxic places to protect workers.

What is a gas sensor?

Gas sensor use physical or chemical reactions to convert the concentration of various gases into electrical signals, and output values after calculation. Widely used to detect toxic and natural gas leaks.

The gas sensor is a device used to monitor the presence or level of gas in a stationary environment. Commonly used in coal mines, petroleum, chemical, municipal, medical, transportation, family, and so on. Gas sensors can measure the presence and concentration of combustible, flammable, toxic gases, or oxygen consumption.

Gas sensors types

There are many gas sensors types, in order to choose the most suitable gas sensor, we need to understand the various sensor characteristics. For example: Which sensor can measure toxic gases? Which sensor is convenient to carry? Which sensor measures more accurately? If you know enough about the sensor, you can definitely make the right choice.

According to different gas types: it can be divided into combustible gas detectors (often using catalytic combustion, infrared, thermal conductivity, semiconductor type), toxic gas detectors (generally using electrochemical, metal-semiconductor, photoionization, flame ionization), Harmful gas detectors (often infrared, ultraviolet, etc.), oxygen (often paramagnetic, zirconia) and other types.

According to different usage methods: it can be divided into portable gas detectors and fixed gas detectors.

According to different sampling methods: it can be divided into diffusion sensors (the sensor is directly installed in the measured environment, and the measurement gas is in direct contact with the detection unit through natural diffusion), pumping sensors (through the suction pump, etc., the gas is sucked into the detection unit. According to whether the gas needs to be diluted, it is divided into complete inhalation and diluted inhalation).

According to different functions: it can be divided into a single gas sensor (only one gas can be detected) and a composite gas sensor (can detect multiple gases at the same time).

According to the different detection principles: it can be divided into semiconductor gas sensor, electrochemical gas sensor, NDIR gas sensor, catalytic gas sensor, thermal conductivity gas sensor, magnetic gas sensor and so on.

Classification according to different working principles is currently the most commonly used. The following article will introduce you to seven gas sensor in detail, as well as their principles and applications:

1. Semiconductor Gas Sensors

A semiconductor gas sensor is a device that uses a semiconductor element as a measuring unit. Its working principle is that the gas undergoes a redox reaction on the semiconductor, which causes the resistance value to change. As the gas passes through the measuring cell, it adsorbs on its surface and reacts. Gas levels are measured by causing a change in conductivity or potential characterized by carrier motion.

This is the most common gas sensor, widely used to detect combustible gas leak detection in homes and factories, and suitable for methane, liquefied gas, hydrogen, etc.

2. Electrochemical Gas Sensors

Electrochemical sensors react with the measured gas and generate an electrical signal proportional to the gas concentration. Most electrochemical gas sensors are current sensors, producing a current that is linearly proportional to the gas concentration. 

The electrochemical gas sensors working principle: the gas passes through a diaphragm that prevents condensation, and this diaphragm also has a dust-proof effect. The gas molecules then diffuse through the filter and reach the working electrode. Here, the gas is oxidized or reduced, and this electrochemical reaction causes a change in the current flowing through the external circuit.

This gas sensors are widely used in gas detection in industrial and civil fields. It can detect ozone, formaldehyde, carbon monoxide, ammonia, hydrogen sulfide, sulfur dioxide, nitrogen dioxide, oxygen and other gases. It is often used in portable instruments and gas online monitoring instruments.

3. NDIR Gas Sensors

NDIR (non-dispersive infrared) gas sensors emit infrared light to make the gas molecules vibrate. The working principle is that different gases can absorb different infrared wavelengths. The more gas there is, the less infrared light can pass through. When infrared rays pass through the gas in the measurement area, the infrared rays resonate with the gas molecules and are absorbed by the gas molecules when the molecules vibrate. 

Understanding the Potential of NDIR Sensors

4. Catalytic Gas Sensors

This sensor is actually a gas detector based on a platinum resistance temperature sensor. A high temperature resistant catalyst layer is prepared on the surface of the platinum resistor, and at a certain temperature, the combustible gas is catalytically burned on the surface. Therefore, the platinum resistance temperature increases, resulting in a change in the resistance value.

6. Photoionization Gas Sensors

A Photoionization gas sensor (PID) works by using photoion-ionized gas to detect gas. Simply put, the gas is irradiated with ultraviolet light generated by an ion lamp, and the gas will be ionized after absorbing enough ultraviolet light energy. The measured gas level is calculated by detecting the tiny current generated by the gas ionization. It can detect volatile organic compounds and other toxic gases from 10ppb to 10000ppm. Many hazardous substances contain volatile organic compounds, and PID is highly sensitive to volatile organic compounds.

It is the most sensitive device for detecting organic volatiles, especially for those gas leaks with very low concentrations, which has incomparable advantages compared to other detectors.


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