Comparison of MOS, NDIR and TDLS sensors

The image visually compares three gas sensing technologies—MOS (Metal Oxide Semiconductor), NDIR (Non-Dispersive Infrared), and TDLS (Tunable Diode Laser Spectroscopy)—using planetary and sun illustrations to symbolize differences in precision and detection capability.

Axetris Know-How

The world of gas sensors features various technologies, each with their own strengths and weaknesses. This article sets out the differences between MOS (Metal Oxide Semiconductor), NDIR (Non-Dispersive Infrared) and TDLS (Tunable Diode Laser Spectroscopy) sensors and shows why TDLS is considered the leading measuring principle, followed by NDIR and MOS.

Author: Michael Krause, Sales Manager GAS, Axetris AG

MOS (Metal Oxide Semiconductor) sensors

Mode of operation: MOS sensors measure the change in the electrical resistance of a metal oxide when it comes into contact with gases. This change in resistance is used to determine the concentration of the gas.

Advantages:

Economical: MOS sensors are inexpensive to manufacture and are therefore widely used.
Simple design: They are robust and easy to integrate.

Disadvantages:

Low selectivity:MOS sensors can be affected by various gases, leading to inaccurate measurements.
High energy consumption: They often require a constant heat source, which increases energy consumption.
Slow response time: The response time may be slower compared to other technologies.

Potential uses: MOS sensors are often used in cost-intensive applications such as household appliances, air quality monitoring or simple industrial applications.

An artistic illustration of the solar system represents MOS (Metal Oxide Semiconductor) gas sensor technology, symbolizing broad-spectrum detection and the ability to sense multiple gases within a complex environment.

MOS sensors detect gases, but with less precision – like distant celestial bodies that you can see without recognizing details. Ideal for simple applications.

NDIR (Non-Dispersive Infrared) sensors

Mode of operation: NDIR sensors measure the absorption of infrared light by gas particles. An infrared beam is passed through a gas chamber and the absorption is measured to establish the concentration of the gas.

Advantages:

Good precision: NDIR sensors offer reliable and accurate measurement for many gases.
Long lifespan: NDIR sensors are durable and require little maintenance.
Wide range of applications: Measure a variety of gases such as CO₂ and methane.

Disadvantages:

Limited selectivity: There may be cross-sensitivities with other gases.
Average response time:The response time is faster than with MOS, but slower than with TDLS.

Potential uses: NDIR sensors are used in environmental monitoring, industrial process controls and indoor air quality measurement.

This illustration of the solar system features the sun prominently, representing NDIR (Non-Dispersive Infrared) gas detection technology—a method that measures gas concentrations using controlled infrared light absorption, symbolized here by the focus on the sun as a source of infrared energy.

NDIR sensors can look much closer: They detect individual “planets” in the gas mixture and deliver more precise results.

TDLS (Tunable Diode Laser Spectroscopy) sensors

Mode of operation: TDLS sensors use a tunable laser to detect specific absorption lines of a target gas. The concentration is measured by the change in light intensity caused by the gas.

Advantages:

High precision and sensitivity: Measurements are very precise and reach ppb (parts per billion) ranges.
Fast response times: TDLS sensors enable real-time measurements.
Low cross-sensitivity: Interference from other gases is minimized by the specific wavelength setting.

Disadvantages:

High costs: Procurement and implementation are cost-intensive.
Complexity: The systems are more complex and require specialist knowledge for operation and maintenance

Potential uses: TDLS sensors are used in demanding areas such as environmental monitoring, industrial process control, leak detection and trace gas monitoring.

The image represents TDLS (Tunable Diode Laser Spectroscopy) gas sensing technology, illustrated by an intense, close-up view of the sun to symbolize high precision and selective measurement using focused laser light.

TDLS sensors get very close – like a telescope that recognizes fine structures on the sun’s surface. This allows them to accurately measure even tiny quantities of gas.

Conclusion

TDLS sensors offer the highest accuracy and sensitivity, but are also the most expensive option. NDIR sensors represent good value for money and are versatile in use. MOS sensors are the most cost-effective solution, but with limitations in terms of accuracy and selectivity. The choice of the right sensor depends on the specific requirements of the application.

However, as TDLS sensors are becoming increasingly compact and cheaper, these sensors are being more and more widely used, and the range of applications is increasing compared to MOS sensors. Axetris AG offers IR emitters for NDIR systems as well as TDLS sensors. We stand for maximum precision and top quality.

Interested in the various technologies from Axetris? Then get in touch.

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