Optical Sensors for Methane (CH₄) and Hydrocarbon (CnHm) Detection with Ultra Low Power Consumption

Optical detection is the staple of gas recognition technologies for a number of reasons: reliability, accuracy, and fitness for a broad range of purposes and areas of application.

Based on the contactless analysis of the concentration of combustible gases, optical sensors measure the difference between reference and measured signals or the energy level of a beam of light of a particular spectrum (typical 3.33 or 3.4 microns for the absorption of hydrocarbon) that passes through a control gas chamber and is reflected onto a sensor.

Compared with other detection technologies, optical gas detection technology by MIPEX, as a minimum, offers the following:

• Minimal signal drift – MIPEX dual-detector infrared gas sensors are designed to minimized signal drift that, in turn, extends calibration and maintenance cycles.
• Immunity to “poisoning” – contamination of the measuring elements of a gas sensor with substances that impair the sensor’s ability to operate with acceptable accuracy. In case of conventional contact-type sensors, high gas concentration may lead to unwanted electrochemical reactions or make them susceptible to the negative effects of the environment that the sensors operate in (presence of dust, grease, sulphur, silicones, etc.).
• Fail-safety – boasting an integrated microcontroller, our dual-beam NDIR gas sensors are capable of running self-diagnostic routines and using special signal processing algorithms for better fail-tolerance, as well as maintaining a linearized output for reliable data reading.
• Quick reaction to growing gas concentration.
• Low maintenance costs, since no parts should be periodically replaced.
• Sensors that contain a metal-ceramic filter, also known as a sinter, should be dismantled for venting or cleaning. MIPEX sensors with a removable filter do not have this flaw.

Innovative optical gas recognition technology by MIPEX

MIPEX leveraged its experience developing high-precision gas sensors to present an all-new line of products that offer a unique combination of ultra-low power consumption, ease of calibration and reliability. MIPEX sensors are already installed in steadily growing number of fixed and portable gas analyzers used at multiple global locations to ensure ultimate safety for people, the environment and sophisticated industrial equipment.

Key advantages of MIPEX infrared gas sensors:

• Extremely low power consumption (under 3 mW across the entire line-up)
• Extended methane measurement range (up to 100% volume concentration)
• High resistance to moisture (negligible reaction up to 98% humidity)
• Long-term stability and ease of calibration
• Integrated controller and a digital interface
• Resistance to catalytic poisons
• Highest level of intrinsic safety (“ia”)
• Absence of the non-removable metal-ceramic filter (sinter)

With tried and tested NDIR technology at their core, MIPEX sensors use advanced optical and electronic components and proprietary designs that give them the competitive edge and make for extended applicability.

In traditional optical sensors, pulsed micro light bulbs are used as the source of light and pyrodetectors as the beam receiver.

MIPEX replaced them with an optron, a special device comprised of a solid LED-based emitter and receiver with an integrated spectral filter, operating within spectral range 3000–4000 nm which resulted in a manifold decrease of power consumption (under 3 mW, about 100 times less than in competing products).

Miniature size of the sensor was obtained by using the systems of effective parabolic mini mirrors with high light transmission efficiency.

Sensor stability in conditions when characteristics (spectrum position, sensitivity and radiation power) of photo detectors and LEDs are subject to serious changes under the action of temperature, was supported by means of development of new LED types, which have optimized radiation spectrum and use of special signal processing algorithm. It provided high stability for sensor within operating temperature range.

Long-term stability of sensors was achieved through the use of photo diodes specially developed for this project based on thin films, which are about 10 times more sensitive than pyroelectric photo detectors and have incomparably higher stability, both temperature and long-term ones, comparing to photonic photo detectors of other types used earlier.

Finally, all MIPEX products offer rich connectivity options via digital, analog and combined interfaces, and can be fine-tuned for specific working environments and operating conditions using specialized software.

All of this makes MIPEX sensors a perfect choice for building new and upgrading existing gas monitoring systems and portable gas detectors adapted for particular gas types and capable of working in the most aggressive environments.

MIPEX IR gas sensors families

The MIPEX line of sensors consists of several families, each optimized for certain device types and/or application scenarios. They are widely used in such safety-sensitive areas as oil and gas extraction, petroleum refining, chemistry and petrochemistry, mining, power generation, wastewater management, biogas extraction and many others.

Our sensors possess a number of unique properties and features that make them the optimal choice for building robust safety systems from scratch and upgrading legacy systems to meet the most stringent technical requirements of today. All of our products offer an exclusively low level of power consumption (up to 3 orders of magnitude in comparison with closes competitors in case of MIPEX-04), support of fully digital (MIPEX-02) and digital/analog connectivity (MIPEX-03), availability in environment-neutral metal or plastic housing for use under any conditions and a lot more.

We are proud of our products and offer them to you: they will provide the optimal combination of performance and resource consumption, a margin of reliability and variability of operating conditions, the possibility of further optimization and the most important – safety.

More information about IR gas sensors by MIPEX and detailed technical specifications can be found in the corresponding sections of our website.

Comparison of Popular Gas Detection Technologies

Catalytic bead sensors, also known as pellistor sensors, have been around for decades. Introduced in the 1960s, it was the first type of combustible gas sensors that replaced caged canaries that had been used by miners since time immemorial. The technology behind these sensors relies on a refractory bead, typically made of alumina, with a porous structure and a platinum wire coil passing through it. The material of the bead is a catalyst that heats up upon contact with a gas due to its combustion. Heating, in turn, changes the electric resistance of the coil, and the drop (relative to the reference bead) is registered as a detection event. Since their introduction to the market around 60 years ago, the design of these sensors remained mostly intact, with some improvements made primarily to the quality of bead coatings and bead size for energy-saving purposes.

Pellistor-based sensors are fairly versatile thanks to their ability to react differently to different gases, both in terms of reaction time and its intensity. This happens due to the following reasons:

• Gas-catalyst reactivity. This factor defines the intensity of the chemical reaction between the catalytic coating and the gas that it comes into contact with. Different bead coatings react to different gases with different intensity.
• Speed of gas diffusion due to Brownian motion. Larger molecules, like long hydrocarbon chains, diffuse through the atmosphere and filters slower than smaller ones, and it takes them more time to reach the necessary concentration that will trigger a chemical reaction with the bead.
• Combustion temperature. Different gases burn (combust) with a different heat output, resulting in a varying amount of heat being passed to the bead and, subsequently, a different voltage surge in the sensor’s circuit.
• Lower Explosive Limit volume. Different gases become combustible at different concentrations, so a gas with a higher LEL will produce a more intense reaction with a catalytic bead.

Disadvantages of the older technology

Although simple and relatively inexpensive, this technology has a number of shortcomings. First and foremost, pellistor sensors use a chemical reaction to detect gas, which causes the sensor’s gradual degradation and even complete coil burn-out if the sensor is exposed to the environment with a high concentration of hydrocarbons. As the result, the sensors’ lifespan gets shorter, they require fairly frequent checks and re-calibration, and most manufacturers only guarantee their stable operation for the first 2 or 3 years.

The second serious drawback of the technology is its susceptibility to chemical poisoning by residue formed by compounds that are typical for the gas and oil industry: silicone vapors, various derivatives of hydrocarbons, hydrogen sulfide and many more. These contaminants gradually decrease the sensor’s ability to efficiently detect gas and eventually render it useless, creating a potentially hazardous situation.

The third flaw of the catalytic bead technology is the lack of intrinsic safety. To prevent combustion from the activation of the catalytic bead’s coating, some models use flame arrestors that may have a dramatic impact on the sensor’s sensitivity. Such a sensor may not be able to react to even a fairly high concentration of particular gases.

The fourth downside of pellistor-based sensors is that since the combustion process requires the presence of oxygen, their efficiency is seriously crippled in low-oxygen environments, while inert and airless spaces (that are often found in the oil and gas industry) render them completely unusable. In such conditions, pellistor-based sensors may remain deaf to the growing gas concentration, even if it’s way past LFL/LEL thresholds.

Finally, catalytic bead sensors are known for their high power consumption that drains the gas detector’s battery, substantially undermining its mobility.

NDIR sensors as an alternative to pellistor-based devices

Optical IR sensors emerged as a powerful alternative to the aging catalytic bead technology. Based on an entirely different approach to gas detection, these new-generation sensors relied on the analysis of the spectrum of light radiated from an IR emitter and reflected onto a receiver inside the measurement chamber of a gas sensor. Different gases absorbed light of a particular wavelength and the difference between the reference value and the actual measurement was interpreted as the level of gas present. The latest generation of IR sensors, such as the MIPEX family of products, take this concept even further by using, among other innovations, a modern nondispersive infrared (NDIR) LED emitter boasting exceptionally low power consumption and longevity. Just like their predecessors, these sensors measure a particular light spectrum to rule out false positives due to dust, water vapors and other substances, and are completely immune to substance poisoning of any sort. Since combustion and chemical reactions are not part of the process, NDIR sensors are shock-proof, intrinsically safe and can be used in fully inert and low-oxygen environments without limitations. Some sensor designs feature a dual-beam/dual-receiver configuration for redundancy and fail-safety – in the unlikely event of one of the components failing, the sensor will remain operational. Finally, the most modern NDIR devices, such as aforementioned MIPEX line of sensors, offer extremely low power consumption: under 3 mWt compared with over 200 mWt typical for catalytic bead sensors.

However, the otherwise perfect optical sensors also have flaws. Due to the limitations of the technology itself, NDIR sensors are not as universal as their pellistor-based counterparts. Configured to monitor a limited spectrum of wavelengths, NDIR sensors are really good at detecting large-molecule gases, such as CH4 and most hydrocarbons, but fail to detect gases like hydrogen and acetylene, which, however, still makes them a perfect choice for multi-gas tools with a focus on hydrocarbons.

Summary

Latest-generation NDIR optical sensors are deprived of the operational limitations of their pellistor-based predecessors and offer the following advantages:

• Dramatically lower power consumption for longer maintenance-free operation in portable and stationary units
• Intrinsic safety thanks to the absence of combustive elements
• Possibility to operate in inert and low-oxygen environments
• Shock-resistance and immunity to chemical poisoning
• Substantially longer lifespan and non-serviceable intervals
• Increased sensitivity to gases with large molecules (mostly hydrocarbons)
• Minimal signal drift and digital interfaces
• Applicability for the most compact, portable and autonomous gas detectors (gas clips)

MIPEX offers an entire family of cutting-edge NDIR sensors based on proprietary technologies and technological know-how’s that are suitable for the most demanding designs. From the core MIPEX-02 model to the revolutionary MIPEX-04, these sensors can be used in a broad range of devices created for the most complex environments and application types.