For nearly 100 years, pellistor/catalytic bead sensors have served as high-tech canaries in the proverbial coal mine. These sensors alert workers in potentially explosive atmospheres -- especially in the mining, gas and oil industries -- to dangerous levels of flammable gasses. In the 1960s, nondispersive infrared detectors (NDIR) were introduced. While both categories of sensors have made potentially dangerous environments safer, and they improve with each passing year, major advances in combustible gas sensor technology have only recently been announced.
Pellistor/Catalytic Bead Sensors
One of the reasons for the staying power of pellistor/catalytic bead sensors is the fact that they’re sensitive to almost all flammable gasses. Even today, pellistor sensors are a commodity product, commanding 60 percent of the market. Why the staying power? In most circumstances, and with proper maintenance, pellistor sensors are reliable.
“Pellistor sensors respond to any combustible gas and they’re relatively inexpensive,” says Dr. Peter Hsi, co-founder of RAE Systems and an expert in sensor technology. However, pellistor/catalytic bead models also have some disadvantages. One is their susceptibility to poisoning. “The sensor is prone to be poisoned by silicon, sulfur and a few other compounds which reduces its operating life,” says Dr. Hsi, who is based in San Jose, Calif.
In environments where even low levels of silicon, lead or phosphates are present, there’s a risk of sensors degrading and of the sensors ultimately being unable to detect the presences of gasses. In situations where flammable gasses are highly concentrated, pellistor sensors burn out quickly. What’s more, pellistor sensors won’t work in low-oxygen environments, including in confined spaces. The only way to know if a pellistor sensor is not functioning is by testing, and if a rigorous and routine testing protocol isn’t in place, personnel could be endangered.
Other challenges with pellistor sensors include the need to set parameters to accurately measure specific gasses, and these sensors’ inability to accurately measure mixtures of flammable gases. Since pellistor sensors require high power -- a minimum of 70 to 100 mA -- they’re limited by the battery life of portable detectors that carry pellistor sensors.
Nondispersive Infrared (NDIR) Sensors
Like pellistor sensors, NDIR sensors have played a fundamental role in workplace safety and gas detection for many decades. In conditions that aren’t appropriate for pellistor sensors, NDIR sensors have been a reliable option. Unlike pellistor sensors, NDIR sensors require relatively infrequent recalibration, and they are not susceptible to poisoning.
“They also have a longer life -- three to five years -- compared to pellistor -- which are typically one to two years,” says Dr. Hsi. Since NDIR sensors are also able to detect gasses in low-oxygen environments, they’re useful in situations where pellistor sensors are ineffective. They require much less power than pellistor sensors, and they don’t burn out, even when exposed to concentrated gases.
One of the challenges with NDIR sensors is their inability to detect hydrogen, an important and potentially dangerous gas in many mining and gas/oil environments. Since NDIR sensors can be tuned to accurately detect only a single gas, they can be ineffective in mixed gas environments. Finally, since the technology required for NDIR sensors is complex and proprietary, these sensors can also be expensive to run.
New Technologies Improve on Legacy Products
New designs are solving some of the problems inherent in both pellistor and NDIR sensors, and combining the best features found in both. For example, a new sensor designed by NevadaNano can measure the concentration of flammable and combustible gas mixtures and it can classify detected gases and mixtures into hydrogen, methane, or light/medium/heavy gas. “The MPS Flammable Gas Sensor can identify what kind of combustible gas is present,” says Dr. Hsi, “and it’s smaller in size and can be lower cost.”
“We’ve designed the MPS Flammable Gas Sensor to address the limitations of both pellistor and NDIR combustible gas sensors,” says Mark Brandemuehl, Sr. VP of Sales and Marketing. With one calibration, the new MPS Flammable Gas Sensor delivers accurate measurement of 12 gases and provides stable, reliable results for years. The sensor can be installed in fixed and portable applications.
“The critical role of a flammable gas sensor is to reliably alert workers when the level of a single gas or mix of gases has become unsafe,” says Mr. Brandemuehl. “We believe the MPS Flammable Gas Sensor’s functionality and reliability sets a new standard for worker safety.”
About the author
Dana Kilroy is a writer and editor, and co-founder of Fior Partners, a communications consultancy. She has written for noted publications including Fast Company and Inc., the New York Times, and the Los Angeles Times. She is based in Reno, NV.