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Gas sensor and its working principle

INTRODUCTION

Gas sensors are crucial devices that detect and measure specific gases in the atmosphere, playing a pivotal role in ensuring safety, environmental protection, and operational efficiency. Whether monitoring air quality in urban settings, detecting toxic gases in industrial environments, or ensuring the safety of workers in hazardous areas, gas sensors are indispensable.

These sensors operate through various principles, including electrochemical reactions, infrared absorption, and thermal conductivity, each tailored for detecting specific gases. From identifying harmful gases like carbon monoxide to quantifying greenhouse gases like methane, gas sensors provide real-time, accurate data critical for decision-making and safety protocols.

An electronic gas sensor is a device that identifies the presence of specific gases and quantifies their levels in the atmosphere. Commonly, these sensors are utilized to track air quality, identify harmful gases, and maintain safety in settings like mines, factories, and healthcare facilities.

The significance of gas detector sensors cannot be overstated, as they deliver accurate, real-time insights into gas levels, thereby safeguarding both the environment and the well-being of employees. Sensors come in several forms, such as electrochemical, infrared, and semiconductor, with each type tailored for the detection of particular gases.

How Gas Sensor works?

A gas sensor functions as a tool that detects and assesses the concentration of designated gases in the surrounding atmosphere. Depending on the type of sensor used, the operational mechanisms may exhibit variations. Each of them is guided by a core principle made up of the subsequent components.

  1. Detection Component

This serves as the key part of the sensor, facilitating interaction with the target gas. The engagement with the sensing material leads to a modification, which can be characterized as either physical or chemical.

  1. Transition to an Electrical Signal

Variations in electrical resistance, current, or voltage are identified and translated into an electrical signal. The intensity of this signal is associated with the level of gas concentration.

  1. Signal Interpretation

Following this, the circuitry within the sensor analyzes and adjusts the electrical signal to generate a relevant output, which indicates the gas concentration in parts per million (ppm).

  1. Result.

The ultimate signal is subsequently shown on a monitoring device or sent to a control system, which can trigger an alarm or activate ventilation systems as required.

The way the sensor operates can differ based on the detection technique that is being used. Examples include electrochemical processes, infrared absorption phenomena, or changes in thermal conductivity.

Categories of Gas Sensors

This overview presents a comprehensive analysis of the key types of gas sensors and the principles that govern their functionality.

  1. Metal Oxide Sensors for Semiconductor Gas Detection

Metal Oxide Sensors for Semiconductor Gas Detection

Functioning Principle

Semiconductor-based gas detection sensors are commonly made from metal oxide compounds. (This may involve materials like tin oxide or zinc oxide), Recognize gases through the measurement of alterations in electrical resistance. The interaction between gases and the sensor leads to the donation or acceptance of electrons by the semiconductor material, which modifies its conductivity. Operating at increased temperatures, the sensor usually exhibits enhanced sensitivity.

  • Regularly Detected Gases:
    • Carbon Monoxide (CO)
    • Nitrogen Oxides (NOx)
    • Methane (CH₄)
    • Ammonia (NH₃)
    • Volatile Organic Compounds (VOCs)
  • Utilizations:
    • Safety Precautions for the Home
    • Automotive Field
    • Products in the Consumer Electronics Sector

2. Gas Sensors Based on Electrochemical Technology

Gas Sensors Based on Electrochemical Technology

Functioning Principle

The detection of gases by these sensors is achieved through a chemical reaction involving the gas and an electrode located in the sensor, creating an electrical signal that is directly related to the level of gas concentration. Within the sensor, there is a sensing electrode (referred to as the working electrode), a counter electrode, and typically a reference electrode, all immersed in an electrolyte medium. As the gas passes through the membrane, it interacts with the electrode, leading to oxidation or reduction processes that create a measurable electrical current.

  • Regularly Detected Gases:
    • Carbon Monoxide (CO)
    • Hydrogen Sulfide (H₂S)
    • Oxygen (O₂)
    • Chlorine (Cl₂)
  • Utilizations:
    • Workplace Safety in Industrial Chemical Surroundings
    • Ecological Oversight
    • Medical Care 

3. Infrared Technology-Based Gas Sensors

Functioning Principle

Gas detection is achieved by these sensors through the measurement of how specific wavelengths of infrared light are absorbed by gas molecules. Gases absorb light at distinct wavelengths, and the sensor evaluates the intensity of light before it interacts with the gas sample and after it has passed through. Changes in light intensity are employed to evaluate the level of gas concentration.

  • Regularly Detected Gases:
    • Carbon Dioxide (CO₂)
    • Methane (CH₄)
    • Hydrocarbons
  • Utilizations:
    • Assessment of Greenhouse Gas Emissions
    • Heating, Ventilation, and Air Conditioning Automation
    • Control of Industrial Processes

4. Catalytic Bead Sensors (Pellistor)

 

Functioning Principle

Catalytic Bead Sensors, commonly referred to as Pellistors, are devices used for detecting combustible gases. This sensor is equipped with two beads, where one bead serves as a catalyst and the other is inert. As the oxidation reaction takes place on the catalytic bead, it produces heat that results in an increase in temperature, subsequently affecting the resistance of the bead. The measurement of resistance disparity between the two beads is proportional to the level of the combustible gas present.

  • Regularly Detected Gases:
    • Methane (CH₄)
    • Propane (C₃H₈)
    • Hydrogen (H₂)
    • Other hydrocarbons
  • Utilizations:
    • Identifying Combustible Gases
    • Coal Mining

5. Photoionization Measurement Devices

Functioning Principle

Ultraviolet (UV) light is employed by Photoionization Detectors to ionize gas molecules. When UV photons are absorbed by a gas, the gas undergoes ionization, producing both positive ions and electrons.  The generated current is proportional to the amount of ionized gas present. The sensitivity of PIDs allows for the detection of gases at remarkably low concentrations, specifically at parts per million (ppm) levels.

  • Regularly Detected Gases:
    • Volatile Organic Compounds (VOCs)
    • Benzene
    • Toluene
  • Utilizations:
    • Environmental Oversight
    • Industrial Chemical Hygiene
    • Management of Hazardous Materials Emergencies

6. Sensors for Measuring Thermal Conductivity

Functioning Principle

The detection of gases by thermal conductivity sensors is based on the understanding that different gases exhibit varying levels of heat conduction. The sensor assesses the thermal conductivity of the target gas by comparing it to that of a reference gas, generally air. When the target gas flows over the heated element in the sensor, it triggers a response to fluctuations in thermal conductivity, which in turn modifies the temperature and resistance of the element.

  • Regularly Detected Gases:
    • Hydrogen (H₂)
    • Helium (He)
    • Methane (CH₄)
    • Argon (Ar)
  • Utilizations:
    • Gas Detection Solutions for Industrial Applications
    • Petro Chemical Process Regulation
    • Hydrogen Manufacturing

7. Acoustic Wave Sensors

Functioning Principle

The operation of acoustic wave sensors involves identifying alterations in the speed or attenuation of sound waves as they move through or along the surface of a sensing material. The engagement of gas with the surface leads to alterations in the mass or properties of the material, thereby influencing the characteristics of the acoustic waves.

  • Regularly Detected Gases:
    • A range of gases is employed, contingent upon the sensing material used and the particular application involved.
  • Utilizations:
    • Ecological Sensing
    • Surveillance of Petrochemical Manufacturing Processes

Conclusion

In various sectors, gas sensors are indispensable technologies that help maintain safety standards, protect the environment, and improve the efficiency of operations. Their ability to detect toxic gases and evaluate air quality is vital for the protection of human life and the smooth functioning of industrial processes.

As technological developments occur, gas sensors are improving, delivering greater accuracy and flexibility in a wide range of environments.