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What are the commonly used gas sensors?

2025-02-25

Common gas sensors can be categorized based on technical principles such as thermal conductivityelectrochemicalcatalytic combustionPIDinfrared, and semiconductor. Let’s dive into the detection principles of each type:


      1. Thermal Conductivity Gas Sensor 
Principle:  Detects gas concentration by measuring differences in thermal conductivity.  
  - Composed of a heating element and a measuring element.  
  - The heating element raises the gas temperature, while the measuring element compares thermal conductivity between heated and unheated states to determine concentration.  



     2. Electrochemical Gas Sensor 

Principle:  Relies on redox reactions between gas molecules and electrodes.  
  - Contains paired electrodes (e.g., working and counter electrodes).  
  - Gas interaction generates a current or voltage proportional to concentration.  
  - Example: Used for detecting CO, H₂S, and O₂.  


3. Infrared (IR) Gas Sensor

Principle:  Exploits gas-specific infrared absorption properties.  
  - Includes an infrared light source and a detector.  
  - Measures absorption intensity at characteristic wavelengths (e.g., CO₂ absorbs 4.26 μm IR light).  
  - Converts light attenuation into concentration values.  


 

     4. Semiconductor Gas Sensor  

- Principle:  Detects gas via changes in semiconductor resistance.  
  - Uses materials like tin oxide (SnO₂).  
  - Gas adsorption alters surface resistance, correlating with concentration.  
  - Common for detecting methane, alcohol, or VOCs.  

5. Catalytic Combustion Gas Sensor

 Principle:   Based on the Wheatstone bridge circuit.  
  - A detection element (catalyst-coated) and a reference element form one bridge arm.  
  - Flammable gas triggers flameless combustion on the catalyst, increasing temperature and resistance.  
  - Voltage imbalance in the bridge reflects gas concentration.  
  - Ideal for methane, propane, and other combustibles.  


      6. Photoionization (PID) Gas Sensor
- Principle: Uses ultraviolet (UV) light to ionize gas molecules.  
  - High-energy UV photons break molecules into ions (positive ions and electrons).  
  - Ion current is amplified and converted to concentration (e.g., ppm-level detection).  
  - Highly sensitive to VOCs and low-concentration toxins.  

Each technology has distinct strengths and limitations:  
- Thermal Conductivity: Simple, durable, but low sensitivity.  
- Electrochemical: High accuracy, but limited lifespan.  
- Infrared: Non-invasive, selective, but higher cost.  
- Semiconductor: Fast response, but susceptible to humidity.  
- Catalytic Combustion: Reliable for combustibles, but requires oxygen.  
- PID: Ultra-sensitive to VOCs, but ineffective for inert gases.