Carbon Dioxide sensors are used in many gas sensing and gas detection products, systems and appliances. These are often called CO2 sensors or CO2 NDIR sensors. These sensors are based on a infra red source (lamp) and photodiode that determines how much IR radiation has been absorbed which correlates to the CO2 detected concentration.
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✅ Low Cost: Have reduced in size and costs over the past 5 years <$20 each NDIR sensor. ✅ Applications: Important for indoor air quality, incubator cell control, hydroponics, and safety. ✅ Lifetime > 5 years: CO2 NDIR sensors last over 5 years. |
⛔ Size: Can get large and bulky and not as small as a thin film semiconducting metal oxide sensor. ⛔ ppm or %vol: Can measure in PPM or %vol. ⛔ Intregrated to Electronics: Needs extra electronics for integration. CO2 NDIR sensor output can be 4-20mA, UART, PWM or 0-5V. |
What is The Principle of Non-Dispersive Infrared?
NDIR stands for nondispersive infrared. It is the most widely used technology for CO2 gas detection. Since CO2 is inert, other chemical techniques (such as electrochemical sensor) cannot be used to sense CO2. These sensors operate by emitting infrared light through a tube or cavity that contains the air sample under test. The air flows towards an optical filter positioned before an IR detector, which measures the light passing through the filter.
NDIR CO2 sensors are designed to emit IR radiation near the 4.26-micron wavelength, which CO2 molecules uniquely absorb. As light travels through the sample tube, CO2 molecules absorb their characteristic IR wavelength, while other wavelengths pass through unaffected.
At the end of the tube, an optical filter blocks all wavelengths except 4.26 microns. The IR detector then measures the remaining light intensity. The reduction in transmitted IR light correlates directly with the CO2 concentration in the sample, allowing for accurate measurement of CO2 levels.
What Are The Components of an NDIR Sensor?
CO2 IR light source
CO2 IR light source is typically an infrared LED or lamp, emits radiation at specific wavelengths, providing the energy needed for CO2 molecule interactions. The gas sample cell, a chamber through which the sample gas passes, allows infrared light to interact with CO2 molecules.
Optical Filters & IR Sensor (usually pyroelectric sensor)
Optical filters select specific infrared light wavelengths known to be absorbed by CO2 molecules, ensuring only the 4.26-micron wavelengths reach the IR sensor, thus enhancing measurement accuracy. The detector, a crucial component, measures the amount of infrared light passing through the gas sample after CO2 molecule interaction, with its signal indicating CO2 concentration.
CO2 Pyroelectric Sensor
The principle of a pyroelectric sensor is based on the pyroelectric effect, which occurs in certain materials that generate a temporary electric potential when exposed to a change in temperature. The pyroelectric sensor has a filter to only absorb CO2 at the 4.26 micron wavelength. When the IR enters, it increases in temperature, inversely proportional to the CO2 concentration.
What is a 4-series CO2 NDIR sensor?
These are standardized sized CO2 sensors that are used in many CO2 meters, CO2 detectors and CO2 analyzers. They are small, consume less energy can allow for standardized design with UART output signal.
Case Study - NDIR CO2 Sensor Circuit
The below circuit illustrates an example NDIR gas sensor circuit utilizing a thermopile detector. While optimized for CO2 detection, this versatile design can accurately measure various gases by simply changing the thermopile's optical filter. This adaptability makes it suitable for a wide range of gas sensing applications beyond just CO2 monitoring.
How Is The CO2 Level Calculated?
The Beer-Lambert Law is fundamental in CO2 detection using infrared sensors and calculating CO2 levels and CO2 concentration. It states that the absorbance of light is directly proportional to the concentration of the absorbing species and the path length of the sample. In CO2 detection, infrared light at a specific wavelength (typically 4.26 μm) passes through a sample chamber. CO2 molecules absorb this light, reducing its intensity. By measuring the difference between the emitted and received light intensity, the sensor can calculate the CO2 concentration. Higher CO2 levels result in greater light absorption, allowing for accurate quantification.
What is the Beer-Lambert Law for CO2 NDIR measurements?
The Beer-Lambert Law equation for CO2 detection can be expressed as:
A = -log(I/I₀) = ε * c * l
Where: A = Absorbance I = Intensity of transmitted light I₀ = Intensity of incident light ε = Molar attenuation coefficient (specific to CO2 at the given wavelength) c = Concentration of CO2 l = Path length of the sample
For CO2 sensors, this is often rearranged to solve for concentration:
c = -ln(I/I₀) / (ε * l)
This equation allows for the calculation of CO2 concentration based on the measured light intensities.
CO2 NDIR Sensor Connecting to Electronics
Electronic engineers use mostly 4 series CO2 NDIR sensor via UART or mA connection.
UART CO2 NDIR Sensor
UART (Universal Asynchronous Receiver/Transmitter) is a widely used serial communication protocol for connecting sensors to microcontrollers. To connect a UART sensor, first identify the TX (transmit) and RX (receive) pins on both the sensor and the microcontroller. Cross-connect these pins: the sensor's TX to the microcontroller's RX, and the sensor's RX to the microcontroller's TX. Ensure the ground pins are connected. Match the baud rates of both devices for proper communication, and verify that the voltage levels are compatible. With these steps, you can establish a reliable UART connection for data exchange.
4-20mA CO2 NDIR Sensor
The 4-20mA current loop is a standard method for transmitting sensor data in industrial applications. In this system, a sensor converts its measurements into a proportional current between 4mA (representing the lowest value) and 20mA (representing the highest value). To connect a 4-20mA sensor, you typically need a power supply (usually 24V DC) and a resistor. The sensor is connected in series with the power supply and the resistor. The voltage drop across the resistor is measured to determine the current, which can then be converted back to the sensor reading. This method is preferred in industrial settings due to its noise immunity and ability to detect connection faults (as 0mA indicates a broken circuit).
Why Is 4.26 Microns Important For CO2 Detection?
The 4.26-micron wavelength is crucial for CO2 detection in NDIR sensors because it corresponds to a strong absorption band of carbon dioxide molecules. At this specific wavelength, CO2 absorbs infrared radiation very efficiently, creating a unique "fingerprint" for detection. This wavelength is chosen to maximize sensitivity and minimize interference from other gases. When infrared light at 4.26 microns passes through a gas sample, the amount absorbed is directly proportional to the CO2 concentration. This precise targeting allows NDIR sensors to accurately measure CO2 levels even in complex gas mixtures or at low concentrations.
How Do Optical Filters Improve CO2 NDIR Sensor Accuracy?
Optical filters in CO2 NDIR sensors significantly enhance accuracy by isolating the specific wavelength of light absorbed by CO2, typically 4.26 microns. These filters act as selective barriers, allowing only the relevant wavelength to pass through while blocking others. This selectivity reduces interference from other gases or environmental factors that could skew readings. By narrowing the detection range, optical filters increase the signal-to-noise ratio, making the sensor more sensitive to small changes in CO2 concentration. Additionally, they help maintain consistent performance across varying conditions, ensuring reliable measurements in diverse environments and applications.
What Is A Waveguide In a CO2 NDIR Sensors?
A waveguide in NDIR sensors is a specially designed path that directs infrared light from the source to the detector. It's a crucial component that allows for miniaturization of sensors while maintaining accuracy. Waveguides often use reflective surfaces or curved designs to extend the optical path length within a compact space. This extended path increases the interaction between light and CO2 molecules, enhancing sensitivity. Modern waveguides may employ folded optics or innovative shapes like "banana" designs to maximize path length in minimal space. By enabling longer light paths in smaller packages, waveguides have been instrumental in developing compact, yet highly sensitive NDIR CO2 sensors.
What Is The Function Of The Reference Channel in a CO2 NDIR sensor?
The reference channel in NDIR sensors serves as a baseline for accurate CO2 measurements. It typically uses a wavelength not absorbed by CO2, providing a constant signal for comparison. This channel helps compensate for variations in light source intensity, detector sensitivity, and environmental conditions like temperature and pressure. By comparing the measurement channel (absorbing CO2) with the reference channel, the sensor can isolate the effect of CO2 absorption from other factors. This dual-channel approach enhances accuracy, stability, and long-term reliability of the sensor. The reference channel also aids in self-calibration processes, helping maintain sensor performance over time without frequent manual adjustments.
How Do NDIR Sensors Maintain Calibration?
NDIR sensors maintain calibration through several mechanisms. Many incorporate self-calibration algorithms that periodically adjust baseline readings, often using the lowest detected CO2 level over time as a reference point. Dual-channel designs with a reference wavelength help compensate for drift in light source intensity or detector sensitivity. Some sensors use sealed reference cells containing known gas concentrations for comparison. Temperature and pressure compensation algorithms adjust readings based on environmental conditions. Advanced sensors may include automatic baseline correction features. Regular exposure to fresh air can help maintain accuracy in some designs. For high-precision applications, periodic manual calibration using certified gas mixtures may still be necessary to ensure long-term accuracy.
How Do NDIR Sensors Compare To Other CO2 Detectors?
NDIR sensors offer several advantages over other CO2 detection methods. Compared to electrochemical sensors, NDIR sensors have longer lifespans and are less prone to interference from other gases. They're more stable than chemical sensors, requiring less frequent calibration. NDIR sensors are faster and more accurate than thermal conductivity detectors for CO2. While slightly less precise than gas chromatography methods, NDIR sensors are more compact and suitable for continuous monitoring. They're more cost-effective and robust than tunable diode laser sensors for many applications. NDIR technology provides a good balance of accuracy, reliability, and cost, making it the preferred choice for many CO2 monitoring scenarios.
How are CO2 NDIR Sensors Used in Real Life?
They are incorporated into various CO2 detectors, CO2 analyzers and CO2 appliances for various applications. These include:
- Industrial situation such as brewery CO2 safety
- Laboratory applications such as incubators operation
- Business and home for Indoor Air Quality
- Leak Detection Applications
- Food and Packaging for Headspace Analysis
- Occupational CO2 Exposure Safety
- Industrial Safety, refrigeration and CO2 dry ice
Can The NDIR (Non-Dispersive Infrared) CO2 Sensor System Produce A Detectable Odor?
No, NDIR CO2 sensor systems do not produce any odor during operation. These infrared-based detection systems work through light absorption rather than chemical reactions.
Final Words
- NDIR CO2 sensors offer reliable, accurate CO2 measurement using infrared absorption at 4.26 microns.
- Technological advancements have led to compact, energy-efficient, and versatile sensor designs.
- Innovations include LED light sources, improved waveguides, and advanced signal processing.
- Environmental challenges are addressed through compensation algorithms and reference channels.
- Improved manufacturing processes are making NDIR sensors more accessible and cost-effective.
- Emerging technologies like photoacoustic spectroscopy promise further miniaturization and sensitivity.
- NDIR sensors are crucial in various applications, from indoor air quality to industrial process control.
About The AuthorDr. Kos Galatsis ("Dr.Koz") is the President of FORENSICS DETECTORS where the company operates from the scenic Palos Verdes Peninsula in Los Angeles, California. He is a subject matter expert on gas sensor technology, gas detectors, gas meters and gas analyzers. He has been designing, building, manufacturing and testing toxic gas detection systems for over 20 years.  Everyday is a blessing for Dr. Koz. He loves to help customers solve their unique problems. Dr. Koz also loves spending time with his wife and his three children going to the beach, grilling burgers, and enjoying the outdoors. Read more about Forensics Detectors here. Email: drkoz@forensicsdetectors.com |