Looking to the future of gas sensing a new galaxy of possibilities

Transcription

1 Looking to the future of gas sensing a new galaxy of possibilities What do the latest images from the Hubble Space Telescope have in common with the sensors inside your gas detectors? Gordon Haddow, Chartered Engineer and Technical Specialist in the Gas Sensors and Thermal Imaging Cameras Engineering Group at e2v, surveys the current scene in industrial gas sensing and then looks at where new Above: the Butterfly Nebula captured using e2v imaging sensors on the upgraded Hubble Space Telescope. Credit: NASA, ESA, and the Hubble SM4 ERO Team. Right: e2v metal oxide semiconductor gas sensors, widely used in the automotive industry. technologies are taking us. There are four major gas sensing technologies widely used today for hazardous area safety applications, each type best suited to particular gases and applications: pellistors, infrared sensors, electrochemical cells and metal oxide semiconductors. Pellistors The mainstay of flammable gas sensing since the 1960s has been the simple pellistor bead, basically a coil of platinum wire coated in a catalyst that is then heated to temperatures around 500 C. The change in coil resistance in the presence of flammable gases such as methane and hydrogen allow the gas concentration to be measured, normally using a non-reacting compensator bead to counteract changes in ambient conditions. The relatively low cost and the simplicity of the electronics needed to monitor them means that pellistors continue to be used extensively. However such high coil temperatures mean they consume a lot of power and also cannot be certified intrinsically safe so they have to be mounted behind a flameproof barrier. There are also a number of other operational issues that users need to be aware of. They can easily be damaged ( poisoned ) by exposure to very low levels (parts per billion) of certain vapours, especially silicones, which may easily be present in many everyday environments. Pellistor sensors also tend to drift over time, so the user must have a regular calibration regime to ensure the sensors read correctly. Modern pellistors are designed to be far more resistant to poisoning than their predecessors but still it remains an issue, especially as there is no way of knowing it has happened until the next test. That is why pellistor sensors should be regularly checked to ensure they provide the correct warnings for hazardous area workers. Infrared sensors The demands of fail-safe operation and higher reliability have caused many users to switch to infrared gas sensing. These types of sensor generally incorporate a pulsing source of infrared radiation that is absorbed by certain gases in proportion to the gas concentration. The infrared wavelength is chosen to suit a particular gas such as methane or carbon dioxide. This method of gas detection is normally reliable and fail-safe although the sensor cost is generally higher than a pellistor. However, unlike pellistors, they are available certified intrinsically safe as well as flameproof. In terms of incorporating them into an instrument, they do require well-designed electronics for optimum performance and a microprocessor to perform linearisation and temperature compensation. So for many gas detector companies the jump to infrared can be a steep learning curve[1]. Electrochemical cell sensors The third main gas sensor technology, often used for the detection of toxic gases such as carbon monoxide, hydrogen sulphide and others, is electrochemical cells. Based on fuel cell technology, these use a chemical reaction of the gas in the presence of oxygen to produce a current proportional to the concentration. These are very low power devices and relatively easy to certify for 44 INDUSTRIAL FIRE JOURNAL SECOND QUARTER

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3 THE FUTURE OF PORTABLE GAS DETECTION e2v has a wide range of electrochemical sensors. Notes 1. To make this a much easier process e2v recently launched an Infrared Gas Sensor Evaluation Kit (IR-EK2) so that instrument manufacturers can get started very quickly. Infrared is now well established in the fixed gas sensor market although the fragile nature of the infrared sources has tended to limit the uptake in portable equipment. 2. e2v recently introduced a new Oxygen electrochemical cell with a much longer lifetime and 55 C upper temperature. Unusually for oxygen sensors it has no lead content enabling it to meet the stringent EU RoHS legislation for the Restriction of Hazardous Substances. 3. e2v has its own inhouse MEMS (Micro- Electrical-Mechanical Systems) design facility based in Switzerland for these types of sensors which has supplied over three million devices to the automotive industry. This same technology is now being introduced into industrial markets. e2v has also used another form of MOS sensor in a pellistor bead style device to give a high temperature hydrogen sulphide detector for environments unsuitable for electrochemical cells. 4. e2v has been addressing a particular need in this market for measurement of up to 100% volume levels of both methane and carbon dioxide using a special twin channel infrared sensor with this capability (IR15TT-R). intrinsically safe applications but their use is normally limited to environments below 50 C and their chemical nature means a typical lifetime is about three years. Users also need to be careful in the choice of sensor as many devices are cross sensitive to a range of other gases[2]. Metal oxide semiconductor sensors A much newer technology in gas sensing are metal oxide semiconductors (MOS). One form of these uses a miniature integrated circuit heater structure to warm up a sensitive layer whose resistance varies with gas concentration. Although these sensors have much poorer accuracy and stability than other types, they are extremely low cost and fast responding and therefore ideal for rapidly detecting a sudden change in concentration[3]. THE FUTURE What of the next 10 years? What changes are we likely to see in gas sensing before the end of this new decade? Lower power and size The power consumed by pellistor and infrared types of gas sensors has limited their use in portable instrumentation to some extent due to battery capacities. Over the last few years rechargeable technology has developed greatly with battery chemistry migrating from Nickel Cadmium (Ni-Cd) to Nickel-Metal Hydride (NiMH) and now various forms of Lithium-Ion (Li-Ion), which offer the best power to weight ratio. The mobile phone and consumer electronic markets will continue to drive the development of new battery technologies with spin-off benefits to the portable gas sensor industry. New versions of Li-Ion cells will mean that portable instruments will be worn rather than be carried. In parallel with the advancing battery chemistries, there will be growing demand for lower sensor power. This is a great challenge for pellistor and infrared sensors but we are investing in future technologies to make this a possibility. It is likely that future versions of these and other sensor types may be radically different to what people have grown used to. Miniaturisation technologies such as MEMS (microelectromechanical systems) have now become common in games consoles and mobile phones. Here too, spin-offs will allow miniaturisation and new forms of tiny gas sensors that have yet to be imagined. Smaller sensors will use much less power and so it will become easier for instruments using them to achieve the necessary ATEX certification. Looking further to the future, ultra-low power sensors will be able to use energy harvesting techniques grabbing energy from the motion of the wearer for example. Reduced cost In a very competitive market there is a constant pressure to reduce sensor price and manufacturers will be looking to minimise production costs using lean manufacturing techniques, automation or perhaps by manufacturing in low cost economies as is common for consumer electronics. However, many companies will first want to maximise the efficiency of their extensive local investments in materials science, physics and chemistry which must be carefully controlled and monitored in production to ensure quality does not slip. Improved performance Sensor designers continue to strive for improved performance in areas such as accuracy, drift, stability, cross sensitivity to other gases and response to environmental parameters such as temperature, pressure and airflow. In some cases it will be difficult to get better performance out of the basic sensor technology, but there will be further advances using better signal processing and compensation techniques. This may result in additional complexity being built into instruments to compensate for a wider range of inputs and to squeeze every last per cent out of the basic sensor. We are also likely to see different ways of operating sensors such as running at lower duty cycles to reduce power consumption. These techniques will require instruments to contain more complex software, which must be robustly designed and rigorously tested, especially in safety related applications. Different gases With environmental issues becoming more prominent, this will impact on the range of gases that people need to monitor. One example is the increase in biogas generation from anaerobic digestion of organic waste[4]. Environmental air quality is also becoming increasingly important and there will be many future requirements for low-cost, air quality monitoring sensors such as MEMS-based metal oxide Semiconductor sensors which are capable of monitoring pollutants such as ozone, carbon monoxide, nitrogen dioxide and ammonia. Ruggedness Finally, the growth of body worn gas sensors will also demand an improvement in toughness for some sensor types. Technologies such as infrared have struggled to dominate the portable market as most IR sensors use a relatively fragile filament-based infrared source that is susceptible to shock such as dropping an instrument. Conclusions The importance of gas sensing is set to grow with increasing requirements for safety and environmental protection across many industries. The current range of gas sensing technologies has served us well but the future holds many new possibilities. Power and size reductions and an improvement in ruggedness will allow a new generation of body worn devices. Ways will be developed to improve performance whilst at the same time reduce cost; new sensors will be targeted at enhancing environmental protection. And in answer to what the latest images from the Hubble Space Telescope have in common with the sensors inside your e2v gas detectors; the sensors in the gas detectors and the NASA imaging sensors were both designed and manufactured by the same company. As e2v imaging sensors on Hubble look back to the origins of the universe, e2v itself continues to look forward, developing tomorrow s technologies to help people work safely and protect the environment here on Earth. 46 INDUSTRIAL FIRE JOURNAL SECOND QUARTER

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5 THE FUTURE OF PORTABLE GAS DETECTION When less does more Similarly to the evolution of the mobile phone which started off life as a giant brick only to evolve into the small, highly functional devices we see today the ongoing metamorphosis of portable gas detection promises much more, writes Steve Forrest, Strategic Telemetry features will find their way into the portable gas detectors of the future. Aspects such as the addition of GPS will allow total visibility on portable device location. Marketing Director, Honeywell Analytics EMEAI. The technology boom of the 80s and 90s has helped to drive down essential component costs, affording gas detection suppliers the opportunity to develop competitive solutions with added value functionality. As a result, today s portable gas detection is small, unobtrusive and highly functional and capable of delivering aspects that make the device easier and quicker to use, thus helping to reduce training requirements and ongoing costs. Aspects like multi-gas capabilities, auto calibration functionality, automatic data logging and plug-andplay pre-calibrated sensors all help to reduce the ongoing cost of gas detection by up to 40% over a three year operating life; an attractive prospect for today s emergency responder. Today s trends, driving tomorrow s devices So what will the future hold for portable gas detection? An examination of current trends provides guidance as to where the biggest innovations in portable gas detection might be; a key trend within the industry is the drive towards enhanced safety and performance. It is likely that there will be some harmonisation across performance standards in an effort to provide tighter controls over how portable products are developed and produced. And when it comes to emergency response, enhanced safety and performance is a highly attractive prospect. Wireless technology will also be instrumental in delivering enhanced safety and helping to reduce ongoing costs. Wireless technologies not only remove the need for wiring, but facilitate automatic communications. Aspects now included in every day devices like the 3G iphone will also find their way into the portable gas detectors of the future. Aspects like the addition of GPS will allow total visibility on portable device location, which is another useful addition that will improve the safety of emergency responders using portable equipment. There are also plans for future devices to include motion sensors so they can alert to a man down situation, should the emergency responder fall to the ground, further improving safety and ensuring that unforeseen incidents are dealt with quickly. Aside from the introduction of new technology currently used in other industries (such as telecommunications), the future of portable gas detection will also include evolutions in current aspects that are already popular. Sensor technology developments have seen improvements in stability, autorecognition of cartridges and pre-calibration functionality, which all reduce the operator s time when changing sensors and calibrating or maintaining the device. Developments in calibration and maintenance will also enable operators to focus on getting the job done, rather than being distracted by non-core activities like equipment maintenance. The use of docking and auto calibration stations such as the MicroDockII from BW Technologies by Honeywell will help operators save time and money by providing a single button solution to bump testing and calibration. Features like this will become increasingly valuable as new regulations are enforced, such as having to always bump test a unit before each use. Portable units like the Impact Pro from Honeywell Analytics, that offer fully portable automatic bump testing, are also expected to become more prevalent. When used with the Enforcer automatic calibrator, calibration of an Impact Pro can be carried out in less than two minutes. Following the trend being seen in the fixed gas detection market place, portables will also move towards IR detection for hydrocarbon and flammable gas detection, rather than catalytic bead. IR offers fail-to-safety operation so as IR costs fall, more and more portable devices will integrate this sensing principle. Multi-gas monitors will become more ubiquitous, as the cost of detecting multiple hazards is reduced through a fall in component costs. It is expected that advances in technology will allow more freedom for the user in terms of defining how monitoring is carried out by the device (continuous monitoring of hazards) and how data can be displayed. As our technological maturity has increased, portable devices have become more intelligent and ergonomic in design. Developments in plastics, gas sensor technology and the design of electronic components have helped evolve the portable monitor. This is a trend that will continue, enabling devices to be less obtrusive, lighter and easier for emergency responders to use. This is excellent news for the responder, who requires a device that does not interfere with any important activities being undertaken but still provides the performance and functionality expected. Whatever the future holds for gas detection, the end user will be instrumental in driving changes. Industry responds to market demands and it appears that the good news for emergency response teams is the drive towards safety; and more simple and intuitive devices that help to reduce ongoing costs, enhance operator ease of use, and deliver enhanced performance. 48 INDUSTRIAL FIRE JOURNAL SECOND QUARTER