For decades, the Catalytic Bead Sensor (CAT/Pellistor) and Non-Dispersive Infrared Sensor (NDIR) have been staples in the gas detection industry. And while they have increased the safety of potentially dangerous working environments, technology is now enabling new, superior gas detection methods.
NevadaNano’s Molecular Property Spectrometer™ (MPS™) is the first truly innovative technology in gas detection to be introduced to the market in over four decades. The MPS sensors address shortfalls in existing technologies, and outperform both Catalytic Bead Sensors and Non-Dispersive Infrared sensors across many dimensions.
Catalytic Bead Sensors (CAT)
CAT sensors have been in use for nearly 100 years. They are popular because they are sensitive to nearly all hydrocarbons, and they are relatively inexpensive. These sensors contain two small beads, one of which is coated with a chemical catalyst while the other has an inert material. When powered on, the beads are heated to a high temperature. If hydrocarbon gas(es) reach the sensing element, the catalyst-coated bead heats up more than the inert one, and the temperature difference can be measured. This temperature difference provides a reading relative to the concentration of the flammable gas present.
And while this is a tried-and-true method of gas detection, there are certain limitations with catalytic bead sensors. They are prone to ‘poisoning,’ which occurs when the sensor comes into contact with higher hydrocarbons, alcohols, ketones, esters, hydrogen sulfide and other sulfur containing compounds. Poisoned sensors often appear to be operating normally – which is an incredibly unsafe hazard for individuals in the area who may be inadvertently exposed to dangerous gases. Calibration of these sensors is also challenging since if it is calibrated to a single gas, the sensor will output inaccurate readings for all other gases.
Non-Dispersive Infrared Sensors (NDIR)
Introduced in the 1960s, NDIR sensors work by using infrared light to detect the different wavelengths of flammable gases. They have an advantage over catalytic bead sensors in that they are not susceptible to poisoning, do not burn out even when exposed to high concentrations of gases, and rarely require calibration. They have a fail-safe so that inoperable sensors can be detected. Additionally, they have a longer life than CAT sensors and can even detect gases in low-oxygen environments. They are more expensive than CAT and require less power than CAT sensors.
But NDIR sensors are not without their limitations. Most notably, they cannot detect hydrogen because this gas does not absorb infrared light. Hydrogen is a potentially dangerous gas across multiple industries, including petroleum extraction and processing environments. They are susceptible to moderate changes in the environment’s temperature and humidity, which can freeze or skew their output during temperature transitions. Their design also allows humidity, fog, and ambient infrared light into the open chamber, all of which can cause interference. And like CAT sensors, if they are calibrated to one gas, the sensor will output inaccurately for all the other gases. NDIR sensors also use proprietary technology, which can make them more expensive than alternatives.
The Distinct Advantage of MPS Flammable Gas Sensors
It is clear that there are drawbacks to both catalytic bead sensors and NDIR sensors for flammable gas detection. The Molecular Property Spectrometer (MPS) introduces real innovation that has distinct advantages over its predecessors. It addresses the shortcomings and combines the best benefits of both the CAT and NDIR sensors.
The MPS sensor uses a micro-electromechanical system (MEMS) transducer, composed of an inert, micrometer-scale membrane with an embedded heater and thermometer. This MEMS transducer measures changes in the thermal properties of the surrounding air and gases in its proximity. The output reading contains multiple measurements – similar to a thermal spectrum – and environmental (temperature, humidity, pressure) data, all of which is used to identify the type of flammable gas present and report a far more accurate concentration.
In short, MPS sensors can measure the concentration of flammable or combustible gases, even mixtures, and classify the detected gas sample into hydrogen, methane, light gas, medium gas, or heavy gas. They can detect the full range of flammable gases quickly, from hydrogen to heavy hydrocarbons. The MPS sensors also have a long-life expectancy (up to five years), and one calibration to methane can deliver an accurate measurement of 12 gases. With NDIR or CAT technology, the user would have to employ detectors for each of these gases individually to get the same results that you can achieve with one MPS detector.
Unlike catalytic bead sensors, the MPS sensors are not susceptible to poisoning since the measurement relies on physical characteristics rather than chemical reactions. They also have a fail-safe and built-in diagnostic capabilities to alert the user if a sensor becomes inoperable or compromised. They also allow for real-time auto-calibration and use less power than CAT sensors and nearly all NDIR sensors. And despite all the advantages that MPS sensors offer, the pricing is still competitive.
The MPS sensor was designed to address the limitations of both CAT and NDIR sensors. It also combines the best features of both. The result is that users can expect the benefits of older technologies without many of the drawbacks. And MPS sensors are flexible, too; they can be installed in both fixed or portable applications. These sensors represent the height of flammable gas detection technology and can reliably alert the user when the level of a single gas or a mixture of gases becomes unsafe. MPS sensors have raised the bar in terms of worker safety expectations in environments where flammable/combustible gases may be present. They are ushering in a new era in gas detection technology.
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