Common gas sensors can be categorized based on technical principles such as thermal conductivity, electrochemical, catalytic combustion, PID, infrared, 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.
2025-02-20
2025-01-25