Keywords: gas sensor, Hanwei, MQ series, air quality sensor, gas detection
Keywords: gas sensor, Hanwei, MQ series, air quality sensor, gas detection
Introduction
Gas sensors are critical components in applications ranging from industrial safety systems to consumer air quality monitors. The ability to detect and quantify specific gases — whether toxic carbon monoxide in a parking garage, combustible methane in a mine, or invisible VOCs in a living room — saves lives and enables healthier environments. The global gas sensor market is projected to reach $4.5 billion by 2030, driven by tightening safety regulations, growing environmental awareness, and the proliferation of smart home devices.
Among gas sensor manufacturers, Hanwei Electronics Group Corporation (汉威科技) stands as China's largest and most established gas sensor producer. Founded in 1998 and headquartered in Zhengzhou, Hanwei has grown from a university spin-off into a publicly listed company (Shenzhen Stock Exchange: 300007) with a comprehensive portfolio spanning semiconductor, electrochemical, catalytic combustion, and NDIR gas sensors. The company's MQ series of semiconductor gas sensors are among the most widely cloned and referenced gas sensor designs in the world, with millions of units deployed annually.
This guide provides a comprehensive overview of gas sensor technologies, detailed coverage of Hanwei's product portfolio, application-specific selection guidance, and practical information on calibration and sensor lifetime. Whether you're designing an industrial gas detection system or a consumer air quality monitor, this guide will help you navigate the complex landscape of gas sensor selection.
Gas Sensor Technologies: A Comparative Overview
Semiconductor (MOS) Gas Sensors
Semiconductor gas sensors, also called metal oxide semiconductor (MOS) sensors, operate on the principle that certain metal oxides change electrical resistance when exposed to target gases at elevated temperatures. The sensing material — typically tin dioxide (SnO₂) or tungsten oxide (WO₃) — is heated to 200–400°C, at which point oxygen adsorption creates a depletion layer on the semiconductor surface. When a reducing gas (CO, H₂, CH₄) reacts with the adsorbed oxygen, electrons are released back to the semiconductor, decreasing resistance. Oxidizing gases (NO₂, O₃) have the opposite effect, increasing resistance.
Advantages: - Very low cost ($0.50–$3.00 per sensor) - Long lifespan (5–10+ years) - Wide detection range (ppm to %LEL) - Simple circuit requirements (voltage divider + ADC) - Robust and tolerant of harsh environments
Disadvantages: - Low selectivity — responds to multiple gases - Requires continuous heating (100–500 mW power consumption) - Warm-up time of 1–10 minutes - Affected by humidity and temperature - Nonlinear response requires calibration
Electrochemical Gas Sensors
Electrochemical gas sensors use a chemical reaction between the target gas and an electrolyte to generate an electric current proportional to gas concentration. The sensor consists of working electrode, counter electrode, and reference electrode immersed in an electrolyte. Target gas diffuses through a membrane and reacts at the working electrode, producing a current.
Advantages: - High selectivity for specific gases - Low power consumption (<1 mW typical) - Linear response over a wide range - Good accuracy (±2–5% of reading) - Direct ppm-level measurement
Disadvantages: - Limited lifespan (1–3 years typical; electrolyte depletes) - Higher cost ($5–$50 per sensor) - Sensitive to temperature and pressure changes - Electrolyte can leak or dry out - Narrow temperature range (-20 to +50°C typical)
NDIR (Non-Dispersive Infrared) Gas Sensors
NDIR sensors exploit the fact that certain gases absorb infrared radiation at specific wavelengths. An NDIR sensor consists of an IR source, a sample chamber, an optical bandpass filter, and an IR detector. The target gas absorbs IR energy at its characteristic wavelength (e.g., 4.26 µm for CO₂), and the reduction in transmitted IR intensity is proportional to gas concentration.
Advantages: - Excellent selectivity (gas-specific absorption wavelengths) - Long lifespan (10–15+ years, no chemical depletion) - High accuracy (±30 ppm for CO₂) - Stable calibration over time - Not affected by other gases
Disadvantages: - Higher cost ($5–$30 per sensor for CO₂) - Larger physical size than semiconductor/electrochemical - Higher power consumption (50–200 mW during measurement) - Limited to gases with IR absorption (CO₂, CH₄, propane, etc.) - Affected by optical contamination
Catalytic Combustion (Pellistor) Sensors
Catalytic combustion sensors detect combustible gases by measuring the heat generated when the gas oxidizes on a catalytic bead. A pair of matched thermistors — one with catalyst (active) and one without (compensating) — forms a Wheatstone bridge. Combustible gas oxidizes on the active bead, raising its temperature and changing its resistance.
Advantages: - Detects most combustible gases (LEL measurement) - Linear response in the %LEL range - Fast response time (<10 seconds) - Good stability and repeatability - Wide operating temperature range
Disadvantages: - Can be poisoned by silicones, sulfur compounds, and halogens - Requires oxygen to operate - Moderate power consumption (100–300 mW) - Lifespan of 3–5 years (catalyst degrades)
Technology Comparison Summary
| Parameter | Semiconductor (MOS) | Electrochemical | NDIR | Catalytic |
|---|---|---|---|---|
| Cost per sensor | $0.50 – $3.00 | $5 – $50 | $5 – $30 | $10 – $50 |
| Power consumption | 100 – 500 mW | <1 mW | 50 – 200 mW | 100 – 300 mW |
| Lifespan | 5 – 10+ years | 1 – 3 years | 10 – 15+ years | 3 – 5 years |
| Selectivity | Low | High | Very High | Low (broad) |
| Accuracy | ±20 – 50% | ±2 – 5% | ±2 – 5% | ±5 – 10% |
| Response time | 5 – 30 s | 10 – 60 s | 2 – 10 s | <10 s |
| Best for | Low-cost detection | Toxic gas (ppm) | CO₂, CH₄ | Combustible gas (%LEL) |
Hanwei Electronics MQ Series: The Industry Standard
The MQ series is Hanwei's flagship line of semiconductor gas sensors. These sensors have become the de facto standard for low-cost gas detection in hobbyist, educational, and commercial applications worldwide. The series includes sensors optimized for different target gases, each using slightly different sensing material formulations and operating temperatures.
MQ Series Product Lineup
| Sensor Model | Target Gas | Detection Range | Heater Voltage | Typical Application |
|---|---|---|---|---|
| MQ-2 | Combustible gas (LPG, propane, methane) | 300–10000 ppm | 5.0V | Gas leak detection |
| MQ-3 | Alcohol vapor | 25–500 ppm | 5.0V | Breathalyzer, drunk driving |
| MQ-4 | Methane (CH₄) | 200–10000 ppm | 5.0V | Natural gas leak detection |
| MQ-5 | LPG, natural gas, town gas | 200–10000 ppm | 5.0V | Domestic gas alarm |
| MQ-6 | LPG, butane, propane | 100–10000 ppm | 5.0V | LPG leak detection |
| MQ-7 | Carbon monoxide (CO) | 20–2000 ppm | 5.0V (alternating) | CO detector |
| MQ-8 | Hydrogen (H₂) | 50–10000 ppm | 5.0V | Hydrogen leak detection |
| MQ-9 | CO and combustible gas | 100–10000 ppm | 5.0V (alternating) | Multi-gas detection |
| MQ-131 | Ozone (O₃) | 10–1000 ppb | 6.0V | Air quality monitoring |
| MQ-135 | Air quality (NH₃, NOx, benzene) | 10–1000 ppm | 5.0V | Air quality monitor |
| MQ-136 | Hydrogen sulfide (H₂S) | 1–100 ppm | 5.0V | Industrial safety |
| MQ-137 | Ammonia (NH₃) | 5–500 ppm | 5.0V | Agriculture, refrigerant |
| MQ-138 | Benzene, alcohol, VOC | 5–500 ppm | 5.0V | VOC detection |
MQ Series Circuit Design
All MQ series sensors follow a similar circuit topology:
- Heater circuit: The heater (H-H pins) is powered by a stable 5V DC supply (or 1.4V for low-power versions), maintaining the sensing element at the required operating temperature.
- Signal circuit: The sensing resistor (A-B pins) forms a voltage divider with a load resistor (RL, typically 10kΩ). The output voltage across RL is read by an ADC.
- Calibration: The sensor must be preheated for 24–48 hours of initial burn-in, then calibrated in clean air to establish the baseline resistance (R₀). Gas concentration is calculated from the ratio Rs/R₀, where Rs is the sensor resistance under gas exposure.
MQ Series Performance Characteristics
While MQ series sensors are inexpensive and widely available, engineers should understand their limitations:
- Selectivity: MQ sensors respond to multiple gases. The MQ-2 responds to LPG, methane, propane, alcohol, and smoke. Software algorithms or additional sensor fusion (with temperature/humidity sensors) can partially compensate.
- Accuracy: Typical accuracy is ±20–50% of reading, adequate for threshold alarming but not for precise concentration measurement.
- Repeatability: Unit-to-unit variation can be significant (±30%), requiring individual calibration for consistent performance.
- Long-term drift: Sensor resistance baseline shifts over time, requiring periodic recalibration (typically every 6–12 months).
Hanwei Electrochemical Sensor Lineup
For applications requiring higher accuracy and selectivity, Hanwei offers a range of electrochemical sensors under the ME and MEMS-ehemical series:
| Sensor Model | Target Gas | Range | Resolution | Lifespan | Application |
|---|---|---|---|---|---|
| ME2-CO | Carbon monoxide | 0–1000 ppm | 1 ppm | 2 years | Industrial CO detection |
| ME2-O2 | Oxygen | 0–30% Vol | 0.1% | 2 years | Confined space entry |
| ME2-H2S | Hydrogen sulfide | 0–100 ppm | 0.1 ppm | 2 years | Sewer, oil gas |
| ME2-NO2 | Nitrogen dioxide | 0–20 ppm | 0.1 ppm | 2 years | Automotive, industrial |
| ME2-SO2 | Sulfur dioxide | 0–20 ppm | 0.1 ppm | 2 years | Industrial emissions |
| ME2-NH3 | Ammonia | 0–100 ppm | 1 ppm | 2 years | Agriculture, refrigeration |
| ME2-CL2 | Chlorine | 0–10 ppm | 0.1 ppm | 2 years | Water treatment |
| ME2-ETO | Ethylene oxide | 0–100 ppm | 1 ppm | 2 years | Sterilization monitoring |
Electrochemical Sensor Advantages Over MQ Series
- Specificity: Each ME sensor is designed for a specific gas, with minimal cross-sensitivity
- Accuracy: ±2–5% of reading vs ±20–50% for MQ series
- Power: <1 mW vs 100–500 mW — enables battery-operated portable detectors
- Linear output: Simplifies calibration and concentration calculation
- Trade-off: Higher cost ($10–$30 vs $1–$3) and shorter lifespan (2 years vs 5–10+ years)
Air Quality Monitoring: PM2.5, CO₂, and VOC
PM2.5 Particulate Sensing
While not a gas sensor per se, particulate matter (PM2.5) sensing is a critical component of air quality monitoring systems. Hanwei offers laser-based PM2.5 sensors that use light scattering to count and size particles:
| Model | Range | Resolution | Lifespan | Interface | Cost |
|---|---|---|---|---|---|
| HPMA115S0-XXX | 0–1000 µg/m³ | 1 µg/m³ | 20,000 hours | UART | $8 – $15 |
| HPMA115C0-XXX | 0–1000 µg/m³ | 1 µg/m³ | 20,000 hours | UART/I2C | $10 – $18 |
These sensors compete with the Plantower PMS5003 and Sensirion SPS30, offering comparable performance at competitive pricing.
CO₂ Sensing (NDIR)
Hanwei's NDIR CO₂ sensors offer an alternative to popular sensors like the Sensirion SCD30 and Senseair SCD41:
| Model | Range | Accuracy | Interface | Cost | Application |
|---|---|---|---|---|---|
| MH-Z14A | 0–2000 ppm | ±50 ppm | UART/PWM/Analog | $8 – $15 | HVAC, indoor air |
| MH-Z14B | 0–5000 ppm | ±50 ppm | UART/PWM/Analog | $10 – $18 | Industrial air |
| MH-Z19B | 0–5000 ppm | ±50 ppm | UART/PWM | $5 – $12 | Consumer air quality |
| MH-Z19C | 0–5000 ppm | ±30 ppm | UART/PWM | $6 – $14 | Improved MH-Z19B |
| MH-711A | 0–5000 ppm | ±50 ppm | UART | $10 – $20 | HVAC, agricultural |
The MH-Z19 series is one of the most popular low-cost NDIR CO₂ sensors globally, widely used in DIY and commercial air quality monitors. Its accuracy of ±50 ppm is adequate for indoor air quality applications (where 400–1000 ppm is the typical range of interest) but insufficient for industrial process control.
VOC Sensing
For volatile organic compound (VOC) detection, Hanwei offers both semiconductor (MQ-135, MQ-138) and electrochemical sensors. The MQ-135 is a general air quality sensor that responds to NH₃, NOx, benzene, smoke, and CO₂. While not truly selective, it provides a useful "air quality index" for consumer applications.
For more accurate VOC measurement, the Bosch BME688 or Sensirion SGP40/SGP41 offer superior performance with built-in algorithms for VOC index calculation — though at higher cost and with dependency on vendor libraries.
Industrial Safety Applications
Combustible Gas Detection (%LEL)
For combustible gas detection in industrial environments (oil and gas, mining, chemical processing), Hanwei offers both catalytic combustion and semiconductor sensors:
Catalytic combustion sensors (for %LEL measurement): - PR-01 (Pellistor): 0–100% LEL for methane, propane, butane, hydrogen - Lifespan: 3–5 years - Cost: $10–$25 - Best for: Industrial gas alarms, portable detectors
Semiconductor sensors (for ppm-level detection): - MQ-2, MQ-4, MQ-5, MQ-6: Low-cost leak detection - Best for: Domestic gas alarms, low-cost industrial alarms
Toxic Gas Detection (ppm)
For toxic gas detection in industrial environments, Hanwei's electrochemical ME series is recommended:
Common industrial toxic gas applications:
| Gas | OSHA PEL | Sensor | Range | Alarm Points |
|---|---|---|---|---|
| CO | 50 ppm TWA | ME2-CO | 0–1000 ppm | 25/50 ppm |
| H₂S | 10 ppm TWA | ME2-H2S | 0–100 ppm | 5/10 ppm |
| NO₂ | 5 ppm Ceiling | ME2-NO2 | 0–20 ppm | 2/5 ppm |
| SO₂ | 5 ppm TWA | ME2-SO2 | 0–20 ppm | 2/5 ppm |
| NH₃ | 50 ppm TWA | ME2-NH3 | 0–100 ppm | 25/50 ppm |
| Cl₂ | 0.5 ppm Ceiling | ME2-CL2 | 0–10 ppm | 0.3/0.5 ppm |
Confined Space Entry Monitoring
Confined space entry requires multi-gas monitors that typically measure: - Oxygen (ME2-O2): Ensure 19.5–23.5% O₂ - Combustible gas (PR-01): <10% LEL - CO (ME2-CO): <25 ppm - H₂S (ME2-H2S): <5 ppm
Hanwei provides all four sensor types, enabling the construction of complete 4-gas confined space monitors. Several Chinese manufacturers produce complete 4-gas detectors using Hanwei sensors at $50–$150 — significantly less than Western equivalents ($300–$800 from Honeywell, Dräger, or MSA).
Calibration and Sensor Lifetime
Semiconductor Sensor (MQ Series) Calibration
MQ series sensors require two calibration steps:
-
Burn-in: New sensors must be powered continuously for 24–48 hours to stabilize the sensing material. During burn-in, the sensor resistance will drift significantly before settling.
-
Baseline calibration: In clean air (known environment), measure the sensor resistance (Rs) and record it as R₀. Gas concentration is then calculated as:
ppm = a · (Rs/R₀)^b
Where a and b are calibration constants from the datasheet sensitivity curve.
- Periodic recalibration: Every 6–12 months, re-establish R₀ in clean air. If the sensor has been exposed to high gas concentrations or operated in humid/dusty environments, more frequent recalibration may be needed.
Electrochemical Sensor Calibration
Electrochemical sensors require span calibration using certified gas:
- Zero calibration: Apply zero gas (clean air or nitrogen) and record the zero output.
- Span calibration: Apply certified calibration gas at 50–80% of full scale and record the output.
- Linearity check: For high-accuracy applications, verify linearity at 2–3 intermediate points.
Calibration interval: Every 3–6 months for industrial safety sensors, or as required by local regulations.
NDIR Sensor Calibration
NDIR sensors are factory-calibrated and have excellent long-term stability. Most NDIR CO₂ sensors require recalibration only every 12–24 months. Some models (MH-Z19C) include automatic baseline correction (ABC), which continuously adjusts the zero point based on the assumption that CO₂ levels periodically return to background (~400 ppm).
Sensor Lifetime Management
| Sensor Type | Typical Lifespan | Failure Mode | End-of-Life Indicator |
|---|---|---|---|
| MQ series (semiconductor) | 5–10 years | Sensitivity loss, baseline drift | Rs/R₀ ratio >3× original value |
| ME series (electrochemical) | 1.5–2 years | Electrolyte depletion | No response to calibration gas |
| NDIR (MH-Z series) | 10–15 years | IR source degradation | Span drift >10% per year |
| Catalytic (PR-01) | 3–5 years | Catalyst poisoning | Response <50% of original |
FAQ
What is the difference between MQ-2 and MQ-4 gas sensors?
The MQ-2 is a general combustible gas sensor sensitive to LPG, propane, methane, alcohol, and smoke. The MQ-4 is specifically optimized for methane (natural gas) detection with higher sensitivity to CH₄ and lower cross-sensitivity to other gases. For natural gas leak detection, the MQ-4 is preferred; for general-purpose combustible gas detection, the MQ-2 offers broader coverage.How accurate are Hanwei MQ series gas sensors?
MQ series sensors typically achieve ±20–50% accuracy of the reading, which is adequate for threshold alarming (e.g., "gas concentration exceeds safe level") but insufficient for precise concentration measurement. For applications requiring higher accuracy, Hanwei's electrochemical ME series offers ±2–5% accuracy, and NDIR sensors offer ±2–5% accuracy for gases like CO₂.How long do electrochemical gas sensors last?
Electrochemical gas sensors typically last 1.5–2 years in continuous operation. The electrolyte gradually depletes as it reacts with the target gas, and the electrode catalyst loses activity over time. High gas concentrations, elevated temperatures, and low humidity can accelerate degradation. Most manufacturers specify the lifespan based on continuous exposure to 50% of full-scale concentration at 25°C and 50% RH.Can Hanwei gas sensors be used in safety-critical applications?
Hanwei sensors are used in numerous safety-critical applications, including industrial gas detection systems that comply with Chinese national standards (GB standards). However, for applications requiring SIL (Safety Integrity Level) certification, ATEX hazardous area approval, or IECEx certification, engineers should verify that the complete sensor module (not just the sensing element) carries the appropriate certifications. For the highest safety integrity levels, sensors from Honeywell, City Technology (Honeywell), or Dräger may be preferred.What is the best sensor for indoor air quality monitoring?
For comprehensive indoor air quality monitoring, a multi-sensor approach is recommended: NDIR CO₂ sensor (MH-Z19C, $6–$14) for ventilation effectiveness, PM2.5 sensor (HPMA115S0, $8–$15) for particulate pollution, and a VOC sensor (MQ-135 for low-cost or BME688 for higher accuracy) for chemical contamination. Temperature and humidity sensors (BME280) should be included for environmental compensation.How do I compensate for temperature and humidity effects on gas sensors?
Temperature and humidity significantly affect gas sensor readings. For semiconductor sensors, humidity increases typically reduce sensor resistance, simulating higher gas concentrations. Compensation methods include: (1) Mathematical correction using a co-located temperature/humidity sensor, (2) Active baseline tracking that adjusts R₀ based on environmental conditions, (3) Using sensors with built-in compensation (some digital sensors include this). For electrochemical sensors, temperature compensation is usually linear and specified in the datasheet.References
- Hanwei Electronics. (2024). MQ Series Gas Sensor Product Catalog. Retrieved from https://www.hanwei-electronics.com/category.php?cid=12
- Hanwei Electronics. (2024). ME Series Electrochemical Gas Sensors. Retrieved from https://www.hanwei-electronics.com/category.php?cid=13
- Zhengzhou Winsen Electronics. (2024). MH-Z19 NDIR CO₂ Sensor Datasheet. Retrieved from https://www.winsen-sensor.com/sensors/co2-sensor/mh-z19b.html
- Occupational Safety and Health Administration (OSHA). (2024). Permissible Exposure Limits (PELs). Retrieved from https://www.osha.gov/annotated-pels
- Bosch Sensortec. (2024). BME688 Gas Sensor with AI. Retrieved from https://www.bosch-sensortec.com/products/environmental-sensors/gas-sensors/bme688/
Meta Description: Comprehensive Hanwei Electronics gas sensor selection guide covering MQ series semiconductor sensors, electrochemical sensors, and NDIR CO₂ sensors. Includes technology comparison, air quality monitoring applications, industrial safety guidance, calibration methods, and sensor lifetime management.