How MPS™ Sensors Outperform Traditional Technologies

Advancements in Gas Detection: Overcoming the Limitations of Traditional Technologies

For decades, the gas detection industry has relied on two key technologies: the Catalytic Bead Sensor (CAT/Pellistor) and Non-Dispersive Infrared Sensor (NDIR). These sensors have significantly increased safety in environments where flammable gases like methane, hydrocarbons, and hydrogen are present. However, while these technologies have served the industry for many years, new advancements in gas detection technology are now offering superior performance. One such breakthrough is NevadaNano’s Molecular Property Spectrometer™ (MPS™), the first truly innovative gas detection technology to be introduced in over four decades.

The Limitations of Traditional Gas Detection Technologies

Catalytic Bead Sensors (CAT) / Pellistors

Catalytic bead sensors, or pellistors, have been in use for nearly 50 years and are known for their sensitivity to a broad range of hydrocarbons. These sensors contain two beads: one coated with a chemical catalyst, and the other made of an inert material. When hydrocarbon gases come into contact with the catalyst-coated bead, a temperature difference is created that can be measured to determine gas concentration. However, while catalytic bead sensors are relatively inexpensive and robust, they have significant limitations.

One of the most critical drawbacks is their susceptibility to poisoning. When exposed to certain gases like higher hydrocarbons, alcohols, and hydrogen sulfide, catalytic bead sensors can become poisoned, resulting in inaccurate readings. This can be dangerous, as the sensor may appear to be working properly while failing to detect hazardous gases. Additionally, catalytic bead sensors are difficult to calibrate for multiple gases. If calibrated for one specific gas, the sensor will inaccurately measure other gases, posing safety risks in environments with mixed gas compositions.

Key Advantages

• Low cost
• Detects the full range of combustible gases

Key Limitations

• Every gas heats the catalytic bead differently, so calibration to a single gas (e.g., methane) means the sensor will output inaccurately for all other gases. (See charts below)
• As the sensor is “used up,” the device needs calibrating.
• Accurate only for the specific gas it is calibrated to.
• Common chemicals—including silicones, chlorine, and acidic gases—deactivate, or “poison,” the catalyst bead. This can happen gradually or within minutes, depending on the environment.
• Flammable gases at high concentrations can “burn up” the catalyst, deactivating the sensors.
• Prolonged exposure to combustible gases may cause a pellistor LEL sensor’s zero reading to shift (or drift), resulting in inaccurate readings.
• Not fail-safe. Poisoned or burned-out sensors appear to be operating normally. Once discovered (via cumbersome bump check or re-calibration, e.g.), the sensor must be serviced and eventually replaced.

Non-Dispersive Infrared Sensors (NDIR)

Introduced in the 1970s, NDIR sensors operate by using infrared light to detect the different wavelengths absorbed by gases. These sensors are less prone to poisoning than catalytic bead sensors and do not burn out when exposed to high gas concentrations. They also offer a longer lifespan and can even function in low-oxygen environments. However, NDIR sensors are not without their limitations.

A major shortcoming of NDIR sensors is their inability to detect hydrogen, a highly flammable and potentially dangerous gas. Additionally, NDIR sensors are sensitive to environmental changes such as temperature and humidity, which can skew their readings. They also require calibration for each specific gas type, much like catalytic bead sensors, leading to the need for multiple sensors if different gases are present. Moreover, NDIR sensors are more expensive and consume more power than catalytic bead sensors.

Key Advantages

• Long life
• Resistant to contamination and poisoning
• Gases may be sensed in anaerobic conditions

Key Limitations

• Hydrogen cannot be detected (because it does not absorb infrared light).
• The open chamber can allow in humidity, fog, and ambient IR light, all of which cause interference.
• Susceptible to moderate changes (0.6 to 2.0 °C/min) in temperature/humidity (e.g., moving from freezing cold outdoors to warm, humid indoors during winter). Some products freeze their output during temperature transitions.
• Transient environmental conditions can cause gas readings to be inaccurate.
• Every gas has a unique absorption profile, so calibration to a single gas (e.g., methane) means the sensor will output inaccurately for all other gases.

MPS™ Sensors: A Proven, Advanced Solution in Gas Detection Technology

NevadaNano’s Molecular Property Spectrometer™ (MPS™) sensors have been setting new standards in gas detection for over seven years. This established technology has already made significant strides in addressing the limitations of traditional gas detection methods, offering superior accuracy and reliability in a wide range of environments.

The MPS™ sensor uses a micro-electromechanical system (MEMS) transducer, which measures changes in thermal properties of the surrounding gases. This system not only measures gas concentration but also provides environmental data such as temperature, humidity, and pressure. By analyzing these multiple data points, the MPS™ sensor can classify gases into categories such as hydrogen, methane, light gas, medium gas, or heavy gas, and report a true concentration reading.

What sets MPS™ sensors apart is their ability to detect up to 14 different flammable gases with a single sensor. Whether it’s hydrogen, methane, or heavier hydrocarbons, the MPS™ sensor provides accurate, real-time detection of all these gases, without the need for recalibration. This eliminates the need for multiple sensors to monitor different gases, simplifying gas detection in complex environments. Legacy flammable gas detection products like Pellistors and NDIR sensors cannot promise the same combination of accurate and reliable detection of multiple gases across the full environmental range.