New sensor technologies are making it possible to measure variables that until recently were too difficult or expensive to sense. According to experts in the field, three areas may cause a transformation in the next few years: nanotechnology-based sensors, wireless sensors, and 3D vision sensors.
Small sensors are not new; micro electromechanical system (MEMS) pressure sensors, accelerometers, and gyroscopes have been available from some years; the airbags in most cars are triggered by MEMS accelerometers. But now chemical sensors based on nanotechnology show considerable promise. An example is a line of nanotech-based sensors from Nanomix that, says president and CEO David Macdonald, form a universal detection platform capable of detecting a wide array of substances with great specificity and high sensitivity. The company’s Sensation technology sensing element, which draws on research done at UC Berkeley, consists of a random network of carbon nanotubes on a silicon substrate. The nanotubes are coated with a chemical recognition layer that causes the electrical resistance of the network to change when the substance to be sensed is present. It’s possible to build sensors for H2, CO2, CO, H2S, NH3, CH4, glucose, explosives, chemical warfare agents, and specific DNA fragments. By combining several different recognition chemicals it is possible to do a signature analysis and identify a particular group of molecules.
The idea of a sensor that requires no wiring has considerable attraction — still more if it can run for a year or more on battery power. Over the past few years a number of wireless protocols have been developed that make it possible to create mesh networks, in which arrays of short-range wireless devices self-organize into a network that can pass data from unit to unit and thence to a factory network, and automatically reconfigure if one unit in the mesh stops working. Individual nodes in the mesh spend most of their time asleep, waking up anywhere from every few minutes to every few days to transmit a brief burst of data.
The best-known standardized protocol is ZigBee, controlled by the ZigBee Alliance, which has more than 100 members, including most of the companies with proprietary systems. ZigBee equipment is used in building automation and home networking, with some industrial applications. ZigBee’s DSSS (direct sequence spread spectrum) transmission method tends to be less resistant to interference than frequency hopping spread spectrum (FHSS). “ZigBee is designed for the home market,” says Conant. “It does a god job in the home market where the IT manager is the owner of the house, the same person who is responsible for buying new equipment. In an industrial setting it’s entirely different.” A number of industry groups are working to standardize industrial wireless communication. Perhaps in response to the Fieldbus wars, the groups have announced plans to coordinate their activities.
The ISA-SP100 committee states that it is working to establish “standards, recommended practices, technical reports, and related information that will define procedures for implementing wireless systems in the automation and control environment at the field level.” In May the committee announced the establishment of two working groups: SP100.14, for “industrial monitoring, logging and alerting applications,” and SP100.11, for “a wide range of applications optimized but not restricted to the unique performance needs of control applications ranging from closed loop regulatory control through open loop manual control.” Carving out a place with so many other standards in place might prove problematic, and part of the working groups’ mission, according to SP100.11 Working Group Chair Pat Kinney of Kinney Consulting LLC., will be to “address coexistence with other wireless devices anticipated in the industrial work space, such as 802.11x, 802.15x, 802.16x, cell phones, RFID, SP100.14, and Wireless-HART.”
The Sensation technology sensing element consists of a random network of carbon nanotubes on a silicon substrate. The nanotubes are coated with a chemical recognition layer that causes the electrical resistance of the network to change when the substance to be sensed is present.