Machine, skid, and robot builders typically incorporate various sensors into their products. They range from simple discrete devices such as pressure sensors to complex multi-variable analog transmitters. Sensors are accessed via hard-wired outputs, digital bus outputs, and/or wireless protocols.
Although the overall market for sensors of all types is expected to exhibit slow growth over the foreseeable future, there are certain sensor technologies that are experiencing rapid growth. One of these areas is wireless sensors.
A September 2002 report from Venture Development Corp. (www.vdc-corp.com) forecasts product shipments for wireless monitoring and control in discrete and process manufacturing applications will increase from $109 million in 2001 to $752 million in 2006, an impressive growth rate in any market.
Wireless sensors can open up new application areas because they can be installed in places that are difficult or impossible to reach with wires. Moving parts in rotating machinery, robot arms, and lift mechanisms are examples of components that are natural fits for wireless technology.
Wireless advantages are compromised or lost if power wiring is needed, so advances in power supply technologies are needed. "Wireless sensors need new power sources that will enable long-term (10 years) operation," says Cleopatra Cabuz, director of global technology in the sensors laboratory for Honeywell Automation and Control Solutions (www.honeywell.com/acs). "New advances in micro fuel cells, micro generators, battery chemistries, and photovoltaics are moving the technology forward, but there is still a long way to go."
Cabuz addresses the power supply side of the wireless-sensor equation, but equally important is power usage. Millennial Net (www.millennial.net) just received $6 million in financing for research and product development of low-power and low-data rate wireless networking technologies.
The company claims wireless networks built with its sensor networking protocol and i-Bean computing devices will be 30 times more power-efficient than Bluetooth wireless systems. The i-Bean is an extremely small and very-low-power self-organizing wireless sensor networking device.
In addition to its own networking protocol, Millennial Net uses a portfolio of radio technologies, including micro-power narrowband solutions as well as IEEE 802.15.4 wireless personal area network (WPAN) components. Market researchers predict the 802.15.4 WPAN market to reach $1.7 billion by 2007.
If wireless sensors with 10-year or more battery life can be economically produced, a host of applications readily could be found. "We foresee maintenance-free wireless networks that are self-correcting and that automatically detect new sensors to optimally route data and information," says Cabuz. "We also envision mobile robots doing intelligent sensor-based wireless data gathering and monitoring for maintenance of large and potentially hazardous industrial operations."
Unmanned aircraft were widely used in the recent war in Iraq, and Cabuz predicts industrial applications for these vehicles. "Micro air vehicles equipped with physical, chemical, and infrared analyzers will fly over refineries, chemical plants, farms, and municipal water and sewage treatment facilities to monitor for leaks, upsets, spills and overall operational and environmental safety," Cabuz predicts.
On the hard-wired front, multivariable sensors are expected to exhibit strong growth. Multivariable pressure-sensing devices combine a pressure output with one or more other types of sensing output (most often temperature) in one unit. The growth rate of these products is expected to be much higher than the industry average.
Thermocouples and other analog sensors are expected to change dramatically because of the IEEE P1451.4 standard. "IEEE P1451.4 will allow vendors to embed calibration and scaling information on a sensor and will provide a protocol to receive and translate this information via a serial digital signal," says Joe Pearson, data acquisition product manager with National Instruments (www.ni.com). "The digital signal will be transmitted via a mixed-mode interface connection that accommodates both the analog measurement signal and a serial digital channel."
Manufacturers incur substantial expense to manufacture thermocouples conforming to designated letter standards such as types J, K, and T. Even the simplest of thermocouple temperature sensors requires a high level of skill to produce, according to a recent white paper by William Schuh and Nathan Frost of Watlow Electric (www.watlow.com).
The white paper says that most thermocouple production problems are the result of calibration constraints placed on the finished product by existing standards. Separating these calibration constraints from basic material performance constraints through the use of the IEEE P1451.4 standard would ease the manufacturing process resulting in lower cost, increased availability, and easier reproducibility.
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