CO2 Sensor Overview and NDIR Working Principle

With growing attention to indoor air quality and environmental health, carbon dioxide (CO₂) concentration has become a key indicator of air freshness. Excessive CO₂ levels can cause drowsiness, reduced concentration, and potentially long-term health effects. Nexisense, a company with over 40 years of gas sensing expertise, is dedicated to developing reliable CO₂ sensor solutions. Often referred to as "the breath perception of air," these sensors capture CO₂ changes in real time, providing essential data for smart ventilation, agricultural control, and industrial safety. This article covers the basic definition, working principle, core technical features, typical applications, and selection considerations to help readers understand this technology comprehensively and apply it effectively.

Working Principle of CO2 Sensors

The mainstream technology for CO₂ sensors is NDIR (Non-Dispersive Infrared), an optical absorption spectroscopy method. CO₂ molecules strongly absorb infrared light at around 4.26 μm wavelength. When infrared light passes through a gas chamber containing CO₂, part of the light is absorbed, reducing the intensity reaching the detector. The sensor calculates CO₂ concentration precisely by comparing the reference and measurement light paths, outputting values in ppm.

This principle relies purely on physical processes, requiring no chemical reaction or oxygen, offering stable measurements and strong resistance to cross-interference. Nexisense optimizes the light source, filters, and detector to maintain high repeatability even in dusty or humid environments. Typical response times range from 10–30 seconds, suitable for scenarios requiring rapid feedback.

Core Technical Features

Nexisense CO₂ sensors are distinguished by high precision and adaptability. Key features include:

High Precision and Long Lifespan

NDIR technology is inherently resistant to interference and is minimally affected by common gases such as CO or VOCs. Accuracy is stable around ±50 ppm. Sensors use high-stability infrared sources and precision optics, with lifespans exceeding 10 years, significantly higher than chemical-based alternatives. Long-term deployment maintains reliable readings and reduces maintenance frequency.

Oxygen-Independent Measurement

Unlike catalytic combustion or some electrochemical sensors, NDIR measurement does not depend on oxygen, performing well in enclosed or low-oxygen environments such as fermentation tanks, underground garages, or greenhouses. This greatly expands application boundaries and prevents failure due to oxygen deficiency.

Wide Monitoring Range

Standard ranges cover 400–5000 ppm, suitable for most indoor and outdoor air quality monitoring needs. Industrial models can extend up to 100% concentration for high-concentration processes. Nexisense product series include TX640-J811 CO₂ Sensor, TX640-J812 Low-Power CO₂ Sensor, Ultra-compact Laser CO₂ Probe, TX750-J122 Infrared CO₂ Gas Sensor, TXZ19D Infrared CO₂ Gas Sensor, TX750-J161 Infrared CO₂ Gas Sensor, TX750-J121 Infrared CO₂ Gas Sensor, TX721-A1 Infrared CO₂ Gas Sensor, TXZ19E Infrared CO₂ Gas Sensor, and TX750-J193 Infrared CO₂ Gas Sensor. These models support multiple output methods (analog, digital, RS485), facilitating system integration.

Low-power versions are ideal for battery-powered or wireless IoT nodes, capable of continuous operation for several months on a single charge.

Typical Application Scenarios

CO₂ sensors demonstrate value across multiple fields:

• Building Energy Saving: Integrated with ventilation systems, sensors increase airflow when indoor CO₂ exceeds 800–1000 ppm, ensuring fresh air while reducing energy waste. Case studies show a 10–20% reduction in HVAC energy consumption and improved occupant comfort and productivity.

• Agriculture and Greenhouses: CO₂ is essential for photosynthesis. Sensors monitor greenhouse concentrations and trigger fertilization systems when levels drop below optimal (typically 800–1500 ppm), promoting plant growth and yield. In livestock farms, sensors regulate ventilation to prevent high CO₂ levels from affecting animal health.

• Industrial Safety: Enclosed spaces such as fermentation facilities, wine cellars, and underground areas are prone to CO₂ accumulation. Sensors provide continuous monitoring, triggering alarms or ventilation if dangerous thresholds (e.g., above 5000 ppm) are approached.

• Environmental Monitoring and Smart Homes: Air quality stations, classrooms, and living rooms display real-time CO₂ levels via apps, coordinating with air purifiers or windows for demand-based ventilation. Low-power models are particularly suitable for long-term, stable operation in these scenarios.

Selection and Usage Recommendations

For industrial-grade applications, NDIR is recommended for accuracy and durability. In home or commercial settings, budget-conscious users may supplement with electrochemical sensors, but NDIR remains more cost-effective long-term. Hazardous environments require intrinsically safe or explosion-proof certified models. Installation should be in central occupied areas, away from vents, heat sources, or windows, with annual calibration recommended.

Nexisense offers customizable solutions, including range adjustment, output protocols (e.g., Modbus), and form factors, helping clients integrate quickly into existing systems. Customization reduces integration difficulty and shortens project deployment time.

FAQ

1. What principle do CO₂ sensors use? Mainly NDIR, measuring CO₂ absorption of specific infrared wavelengths.

2. What is the typical accuracy of NDIR sensors? ±50 ppm, with minimal long-term drift.

3. Why is NDIR suitable for enclosed spaces? Measurement does not depend on oxygen and works in low- or no-oxygen environments.

4. What is a normal indoor CO₂ level? Outdoor ~400 ppm; good indoor air quality is below 800 ppm.

5. How does the sensor function in greenhouses? Monitors and controls CO₂ to enhance photosynthesis and crop yield.

6. How long is NDIR sensor lifespan? Typically over 10 years under normal conditions.

7. How to distinguish NDIR from electrochemical CO₂ sensors? NDIR is more stable, oxygen-independent, and longer-lasting; electrochemical is cheaper but environmentally sensitive.

8. What output interfaces are supported? Analog voltage, 4-20 mA, RS485, digital I²C, etc.

9. Installation considerations? Avoid direct sunlight, heat, and strong airflow; recommended height 1.2–1.5 m.

10. Can custom ranges be provided? Yes, Nexisense supports flexible ranges from hundreds of ppm up to 100% high concentration.

Conclusion

NDIR-based CO₂ sensors, with high accuracy, oxygen independence, and wide monitoring range, are essential tools for modern environmental management and energy optimization. From building ventilation integration to precise greenhouse fertilization and industrial safety, these sensors demonstrate practical value across domains. Backed by extensive expertise, Nexisense offers full-scenario compatible products and customization services, enabling healthier and more efficient space management. Choosing a reliable CO₂ sensor represents not only a technical upgrade but also a commitment to health and responsibility.