Ready for real-time wireless control?
A large percentage of those using wireless technology in industrial applications are applying it to control applications, or both control and monitoring, according to a recent study by Venture Development Corp . (VDC). Further analysis indicated that control applications are largely in setup/maintenance; and reliability concerns are inhibiting adoption for operational real-time usage.
Input of study respondents on the question of “industrial monitoring” vs. “control applications” found:
What applications use which wireless products? Data communication, controller programming, and controller maintenance were the three most identified, both currently and planned. So wireless use in machine- and process-setup and troubleshooting is far more common than for operational real-time control.
Users also identified wireless control of cranes/hoists—over 25 years a well-established industrial market for wireless operational real-time control. While it’s “operational real-time” control, it’s not fully automatic—the operator is an integral part of the control loop.
Two big problems inhibit operational real-time control. True real-time automated control poses a much greater concern to implementers than monitoring control applications. Two most identified user problems encountered in RF/microwave wireless industrial monitoring and control are:
ound in applications with slowly changing variables, such as temperature and flow control of slowly fluctuating processes, or for operator-based control, rather than in automated systems where high-speed machinery is being controlled.
Controlling slow processes—with lesser data rates—requires less bandwidth. Therefore many existing, industrial, operational real-time wireless-control applications function in the 400 MHz, 800 MHz, and 900 MHz bands that provide adequate channel bandwidth. Higher-speed applications can require more bandwidth, necessitating higher frequency bands, such as 2.4 GHz or 5 GHz. Generally, moving to higher frequency bands makes signal drop-outs/blockage worse. Interference varies with the local environment.
A key justification of wireless is wiring cost reduction; savings tend to be greater for large distributed systems (often slow process-type applications, rather than high-speed machinery). Thus, there may be little savings in wiring for many discrete manufacturing operations, and use of wireless technology for operational real-time control may not be attractive. Furthermore, higher RF/microwave frequency band operation may be needed to ensure adequate bandwidth. Usually, as the frequency goes up, so does RF/microwave component cost. However, wireless technology may still be attractive for use with portable operator interface terminals for machine setup/troubleshooting.
It appears that the greatest near-term potential for operationalreal-time usage will be for slow-moving, process industry applications, where data transmission faults don’t pose a serious risk. For these, VDC analyst Jake Millette points out, “Wireless operational real-time control holds many potential advantages over wired solutions, but even here small steps must be taken as mistakes can be expensive.”
It’s expected RF/Microwave wireless technology in operational real-time control will eventually extend into other applications in discrete and process manufacturing.
For more on wireless trends and technology, also see Control Engineering ’s “
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— Richard Phelps, senior editor, Control Engineering