Analog → PLC / DCS
- Voltage signal reads concentration directly
- Matches industrial analog inputs
- No protocol work — wire and read
Best for: fixed online monitoring on PLC / DCS, or retrofitting legacy systems.
Shanghai Yixin G4 / G4(P) / G7 / G8 / NDIR Infrared Gas Sensors
Shanghai Yixin NDIR Infrared Gas Sensors
21 NDIR infrared gas sensors on a dual-wavelength optical path — covering combustible gases (methane / isobutane / acetylene), full-range CO₂ (5000 ppm to 100% VOL across 7 ranges), SF₆ leak detection and indoor air-quality modules. No oxygen dependency, no catalytic poisoning, minimal long-term drift, Ex ia I Ma / IIC T4 Ga dual explosion-proof certification, -40 ℃ to +70 ℃ operating range, 18-month warranty.
- 21 Product Models
- 4 Product Lines
- 100% VOL Maximum Range
- -40~+70 ℃ Operating Temp (combustible)
- 18 mo Warranty
Why NDIR Infrared Over Catalytic Combustion or Electrochemical?
NDIR measures a gas's absorption of its characteristic infrared wavelength — not heat of combustion or an electrochemical reaction. That gives it three things catalytic combustion and electrochemical sensors cannot do: works without oxygen, no poisoning risk, and a range that reaches 100% VOL.
| Aspect | Catalytic / Electrochemical | NDIR Infrared (this range) |
|---|---|---|
| Operating Principle | Catalytic measures heat / electrochemical measures current | Infrared absorption spectroscopy at the gas's characteristic band |
| Oxygen Dependency | Catalytic combustion needs oxygen | No oxygen dependency — works in inert atmospheres |
| Poisoning Risk | Catalytic prone to silicone poisoning / electrochemical may poison | No catalytic poisoning, long-term stable |
| Range Ceiling | Mostly %LEL level | Up to 100% VOL |
| Recalibration Frequency | Requires periodic recalibration | Minimal long-term drift, no frequent recalibration |
| Best For | Conventional combustible-gas alarms | High concentration, harsh industrial, continuous online, SF₆ leak detection |
Selection Guide
Five Steps to Specify an NDIR Sensor
Specifying an NDIR sensor is less about picking a model than about clarifying what level of which gas you measure. Finish the five steps and the model falls out naturally.
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① Fix gas and level
Combustibles (methane / isobutane / acetylene) → G4 combustible family in %LEL or %VOL; CO₂ → G4 CO₂ family across 7 ranges from 5000 ppm to 100% VOL; SF₆ leak detection → G7 / G7C; indoor air quality → G8 series.
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② Choose the output
Analog 0.4 – 2.0 VDC for PLC / DCS; TTL UART (default 9600 bps) for MCU and instruments; G7C supports Modbus RTU for industrial buses.
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③ Check the temperature range
Combustibles / hydrocarbons -40 ℃ to +70 ℃, wide range for outdoor and harsh sites; CO₂ types 0 ℃ to +50 ℃ (extendable to -40 ℃ to +70 ℃). Always confirm the range for outdoor or cold-store applications.
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④ Match the explosion-proof spec
The G4 family carries Ex ia I Ma / Ex ia IIC T4 Ga dual certification and IP65 (optional breathable membrane) for mining and chemical hazardous areas; G8 IAQ modules are non-explosion-proof, indoor use only.
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⑤ Match IAQ module features
G8(S) / G801C are single CO₂ modules with auto-calibration; G805C / G805CE are 5-in-1 (CO₂ + HCHO + PM2.5 + temp/RH) for fresh-air systems and air-quality monitoring stations.
Which Shanghai Yixin Line Do You Need?
Four lines split by application: combustible-gas alarm, full-range CO₂, SF₆ leak detection, and indoor air quality. Decide the scenario first, then the range within that line.
| Specification | G4 Combustible | G4 Full-range CO₂ | G7 / G7C SF₆ Leak | G8 Air-Quality Modules |
|---|---|---|---|---|
| Target Gas | Methane / Isobutane / Acetylene | Carbon Dioxide CO₂ | Sulfur Hexafluoride SF₆ | CO₂ + HCHO + PM2.5 + temp/RH |
| Typical Range | 0–100% LEL / 5% / 100% VOL | 5000 ppm to 100% VOL (7 ranges) | G7 0–1000 ppm (extendable 2000/3000), G7C 0–1500 ppm | IAQ level |
| Resolution | 1% LEL / 0.01% VOL | 1 ppm to 0.01% VOL | see datasheet | see datasheet |
| Response Time T90 | < 20 s (free diffusion) | < 20 s (free diffusion) | see datasheet | see datasheet |
| Operating Temp | -40 ℃ to +70 ℃ | 0 ℃ to +50 ℃ (extendable -40 ℃ to +70 ℃) | see datasheet | 0 ℃ to +50 ℃ |
| Explosion-Proof | Ex ia I Ma / IIC T4 Ga, IP65 | see datasheet | G7C supports Modbus RTU | Non-Ex (indoor only) |
| Output | Analog 0.4–2.0 VDC + UART | Analog 0.4–2.0 VDC + UART | Modbus RTU (G7C) | Analog + UART |
| Best For | Gas alarms / LPG / industrial explosion-proof | HVAC / greenhouse / fermentation / flue gas | Power-grid GIS SF₆ leak detection | Fresh-air systems / air-quality stations |
G4(P) is the upgraded G4 with higher resolution and faster response (T90 < 25 s), covering methane and CO₂ (5000 ppm / 5%VOL / 100%VOL) with full-range temperature compensation.
Three Typical Ways to Interface an NDIR Sensor
The same NDIR sensor offers different outputs and protocols depending on what it connects to. Pick the downstream first, then back into the model — easier than shopping the spec table cold.
UART → MCU / Instrument
- Digital concentration value directly
- Default 9600 8N1
- Suits self-developed instrument MCUs
Best for: self-developed gas detectors and main boards needing digital calibration and logging.
Modbus RTU → Industrial Bus
- Standard Modbus RTU protocol
- Multi-drop networking supported
- Suits SCADA and protection relays
Best for: multi-point SF₆ leak monitoring in power GIS rooms, interfacing SCADA / protection systems.
The G8 IAQ family also offers auto-calibration and 5-in-1 (CO₂ + HCHO + PM2.5 + temp/RH) configurations — see each product page and datasheet.
21 NDIR Infrared Model Matrix
Grouped by target gas across combustible, CO₂, SF₆ and air-quality lines. Click any model for its datasheet.
Methane
Carbon Dioxide
- Carbon Dioxide NDIR Infrared Gas Sensor G4441 Datasheet →
- Carbon Dioxide NDIR Infrared Gas Sensor G4442 Datasheet →
- Carbon Dioxide NDIR Infrared Gas Sensor G4443 Datasheet →
- Carbon Dioxide NDIR Infrared Gas Sensor G4444 Datasheet →
- Carbon Dioxide NDIR Infrared Gas Sensor G4445 Datasheet →
- Carbon Dioxide NDIR Infrared Gas Sensor G4446 Datasheet →
- Carbon Dioxide NDIR Infrared Gas Sensor G4447 Datasheet →
- Carbon Dioxide NDIR Infrared Gas Sensor (Upgraded) G4(P)-CO2 Datasheet →
- Carbon Dioxide NDIR Infrared Gas Sensor G8(S) Datasheet →
- Carbon Dioxide Infrared Sensor Module G801C Datasheet →
Sulfur Hexafluoride
NDIR Infrared Sensor FAQs
What's the difference between NDIR and catalytic combustion?
Catalytic combustion measures the heat a combustible gas releases when it burns — it needs oxygen, is prone to silicone poisoning, and tops out around %LEL. NDIR measures the gas's absorption of its characteristic infrared wavelength — no oxygen dependency, no poisoning, range up to 100% VOL. So pick NDIR for inert atmospheres, high concentrations or long calibration-free runs; catalytic combustion still works for conventional alarms on a tight budget.
How do I choose between G4, G4(P), G7 and G8?
By scenario: combustible-gas (methane / isobutane / acetylene) alarms → G4 combustible family; for higher resolution and faster response (T90 < 25 s) → G4(P) upgrade; power-grid GIS SF₆ leak detection → G7 / G7C (G7C with Modbus RTU); indoor air quality and fresh-air systems → G8 family (G8(S)/G801C single CO₂, G805C/CE 5-in-1).
How do I size the CO₂ range?
Size by application ceiling: indoor air quality 5000 ppm; greenhouse and fermentation 1% – 5% VOL; flue gas and high-concentration processes 10% – 100% VOL. The G4 CO₂ family offers 7 ranges — 5000 ppm / 1% / 2% / 5% / 10% / 20% / 100% VOL. Pick to your maximum concentration; leave headroom rather than over-ranging.
Why use NDIR for SF₆ leak detection?
SF₆ is strongly electronegative — neither electrochemical nor catalytic principles fit it. NDIR detects SF₆ at its characteristic infrared absorption band: high sensitivity and immune to electric-field interference, the standard approach for power-grid GIS SF₆ leak detection. G7 range 0–1000 ppm (extendable to 2000/3000); G7C 0–1500 ppm with Modbus RTU for protection systems.
What does Ex ia I Ma / IIC T4 Ga mean?
Ex ia is intrinsic safety (the highest protection level); I Ma is the underground mining rating; IIC T4 Ga is the highest surface gas-environment category (IIC includes hydrogen and acetylene) with T4 temperature group (≤ 135 ℃) and Ga equipment protection level. Dual certification means the G4 family works in both underground mining and chemical hazardous areas, with IP65 and an optional breathable membrane.
How often does it need recalibration?
NDIR has minimal long-term drift and needs no frequent recalibration. The G8 IAQ family carries auto-calibration (ABC algorithm) — essentially maintenance-free in normal indoor settings. For G4 / G7 in harsh industrial or high-precision settings, periodic zero and span checks are recommended; see each datasheet for the interval.
How do I get a quote, samples and datasheets?
Every datasheet is downloadable from its product page on this site. For samples and volume pricing, send us the target gas, range, explosion-proof requirement and annual volume through the contact form or by email, and we will quote the matching model with lead time.
Need Help Choosing a Model?
Send us your target gas, range and explosion-proof requirement — we will match the model and quote it. Datasheets for all 21 NDIR infrared sensors are available to download now.