Introduced in the 1960s, Non-Dispersive Infrared (NDIR) sensors have been a staple in the gas detection industry for decades. These sensors work by using infrared light to detect the different wavelengths of flammable gases. Many advantages come with using NDIR technology, but they also come with some drawbacks that any user should consider.
NDIR Technology Overview
Prior to the development of NDIR sensors, catalytic bead sensors were primarily used for detecting gas leaks. NDIR sensors have many advantages over catalytic bead sensors. They are not susceptible to poisoning, do not burn out even when exposed to high concentrations of gases, and rarely require calibration. NDIR sensors also have a fail-safe so that inoperable sensors can be detected.
Additionally, they have a longer life than catalytic bead sensors and can even detect gases in low-oxygen environments. They are also inexpensive and require less power than catalytic bead sensors. Since NDIR technology addressed many of the limitations found with catalytic bead sensors, they were a giant leap forward for gas detection technology, especially when used for detecting methane.
NDIR Sensors & Hydrocarbons
Despite the advantages they have over catalytic bead sensors, NDIR sensors are not without their limitations. Most notably, NDIR sensors cannot detect hydrogen because this gas does not absorb infrared light. Hydrogen is a potentially dangerous gas in many mining and petroleum extraction and processing environments.
NDIR sensors are incredibly accurate at detecting methane, but they do not work well when multiple hydrocarbon-based gases are present. In these situations, they are likely to provide false readings. Unfortunately, in many industries, detecting hydrogen and hydrocarbons is critical in maintaining a safe workplace. Hydrogen is commonly used in petroleum refining, treating metals, producing fertilizer, and processing foods.
And the hydrogen market is projected to grow to exceed $160 billion by 2026, meaning reliable detection methods for hydrogen will become increasingly important.
Hydrogen is a flammable and combustible gas frequently used in the same vicinity as other flammable materials and gases. It has lower ignition energy than gasoline or natural gas and once ignited, it can rapidly spread or lead to a severe fire or explosion. Hydrogen is simply a very dangerous gas. And when hydrogen is present, there is often a greater risk of exposure to other dangerous gases, such as butane and methane.
Exposure to even low concentrations of hydrogen can result in nausea, headaches, delirium, tremors, convulsions, and irritation of the skin and eyes. At higher concentrations, an individual can rapidly lose consciousness, and the effects of hydrogen on the central nervous system make it deadly in a short amount of time.
In order to protect the workplace, its workers, and the profitability of the business, employers in industries that use hydrogen and hydrocarbons need to have reliable and accurate gas detection sensors. NDIR sensors have a severe limitation due to their failure to detect hydrogen entirely, and that they often provide false readings in environments with mixed hydrocarbons.
Other Limitations with NDIR Sensors
In addition to their inadequacies when encountering hydrocarbons, NDIR sensors are susceptible to moderate changes in the environment’s temperature and humidity, freezing their output during temperature transitions. They function poorly in extreme environments or where there is a rapid change in conditions.
The design of NDIR sensors also allows humidity, fog, and ambient infrared light into the open chamber, all of which can cause interference. This interference can impact their reliability, providing another opportunity for these sensors to fail and potentially expose workers to risk. NDIR sensors also typically require a great amount of power to function, and they require frequent calibration which contributes to a higher total cost of ownership.
And since NDIR is a proprietary technology, the sensors themselves can be quite expensive when purchased.
The limitations of NDIR sensors are great, and any potential user should understand the pitfalls of using these sensors before purchasing them. Recent advances in gas detection mean that more suitable products are available to help employers ensure their workplace remains safe and their assets are protected.
Selecting the Right Sensor
Selecting the best sensor for your environment often means understanding the characteristics of each type – including their limitations – and understanding the environmental conditions where it will be in use. Before selecting a hydrogen sensor or detector, several functional parameters should be considered:
- Performance: The optimal performance of hydrogen sensors is best achieved when the most suitable sensor is selected for a specific application. Sensors can be purchased with a wide operating range, optimized sensitivity below the lower flammability limit (LFL) in air, fast response times, continuous operation, and for use in wet conditions. Considering what factors may be present when testing can help you identify the most suitable sensor.
- Lifetime: In order to determine current and future application and operating costs, as well as identify replacement and maintenance needs, a suitable lifetime should be identified.
- Reliability: Sensors must have long-term reliability that produces consistent results. It is also good to gain a full understanding of any testing conditions that can cause false alarms or damage the sensor in a way that will impact its reliability.
- Cost: While some lower-end sensors may come with minimal costs, the performance, reliability, and lifetime value of the sensor should not be sacrificed. The risk that comes with an unreliable sensor is too great to cut corners. And when determining cost, it’s crucial that you consider more than just the initial purchase price; users should also factor in calibration costs, replacement costs, and other associated costs.
All of these factors should be considered before investing in any gas detection technology, including NDIR sensors.
Alternatives to NDIR Sensors
The Molecular Property Spectrometer™, or MPS™, provides the benefits of NDIR sensors while also overcoming its major limitations. It offers the best of both catalytic bead and NDIR sensors without the limitations of either. This sensor uses a micro-electromechanical system (MEMS) transducer to measure changes in the thermal properties of the surrounding air and gases in the near vicinity.
The output reading contains multiple indicators and environmental data to identify the types and concentrations of any flammable, combustible, or hazardous gases nearby.
| Gas | MPS Sensor | NDIR |
| Methane | Detected: 12 seconds
Accurate LEL reading: 20 seconds |
Detected: 12 seconds
Accurate LEL reading: 20 seconds |
| Butane | Detected: 12 seconds
Accurate 50 %LEL reading: 41 seconds |
Detected: 30 seconds
Accurate reading of 50 %LEL: Failed* *Sensor read 125 %LEL |
| Hydrogen | Detected: 12 seconds
Accurate 50 %LEL reading: 40 seconds |
Detected: Failed
Accurate reading of 50 %LEL: Failed* *The sensor read 0 %LEL for the entire test |
MPS gas detection technology is a tremendous leap forward in the capabilities of gas detection sensors. They overcome the limitations of both NDIR and pellistor sensors while offering a greater level of flexibility.
These sensors are more accurate and reliable across nearly all environmental conditions. And accuracy and reliability are of the utmost importance when working with flammable gases. MPS sensors ensure that the workplace stays safe and that users can be alerted to the presence of all flammable gases in their environment.