Going Wireless: Numerous Concerns
Since industrial wireless is still an evolving technology, many manufacturing engineers are reluctant to try it in their plants. Jeremy Bryant, an automation technology specialist at Siemens Energy & Automation Inc. (Alpharetta, GA) says several concerns are hindering widespread implementation, including a perceived higher cost than wired solutions; concern about RF interference; lack of knowledge and experience of the wireless technology; concern about reliability; concern about signal reception, drop outs and blockage; concern about security in wireless solutions; and confusion over standards.
Cost is a big concern, because wireless sensors can be three times more expensive than traditional technology. However, "a lot of companies look at initial cost, rather than overall system lifetime cost," says Jesse Hayes, product manager for automation components at Schunk Inc. (Morrisville, NC). "When you factor in maintenance costs and other issues, wireless technology may actually be more economical."
Jan-Erik Frey, director of wireless technology and business development at ABB Automation Technologies (Vasteras, Sweden), recommends making a full cost analysis and looking at the life cycle of the installation when estimating cost savings. "Many times, when wireless alternatives are disqualified, the reason is that customers focus primarily on the difference in hardware and software costs, thereby neglecting the savings discovered in full cost analyses," he points out.
Some manufacturers are reluctant to embrace wireless technology because of concerns over reliability and interference. According to Kevin Prouty, senior director of manufacturing solutions at Symbol Technologies Inc. (Holtsville, NY), most of the concerns about reliability are the same arguments that held Ethernet back for years. "In the end, wireless will be fully implemented in SCADA and HMI-type applications where reliability at the nanosecond level are not a concern," he points out.
Most industrial wireless applications involve slowly changing variables, such as temperature control or flow control, rather than in automated systems where high-speed machinery is being controlled. "Controlling slow processes also requires less bandwidth, as data rate requirements are lower," notes says Jake Millette, an analyst at Venture Development Corp. (VDC, Natick, MA). "Thus, many of the existing industrial operational real-time control applications using wireless technologies operate in the available RF spectrum bands in the 400-, 800- and 900-megahertz bands where there is adequate channel bandwidth for these applications.
"However, higher speed applications can require more bandwidth, which in turn may necessitate operating in higher microwave frequency bands such as 2.4 gigahertz or 5 gigahertz," adds Millette. "In general, moving to higher frequency bands makes the problem of signal drop outs-blockage worse. With regards to whether interference is better or worse, this depends upon the local environment where the system will operate."
The biggest stumbling block to widespread acceptance of industrial wireless technology is confusion over standards. According to Harry Forbes, a senior analyst at ARC Advisory Group Inc. (Dedham, MA), manufacturers will only make large deployments of wireless devices when they are based on standards. He says several options are currently available, including Bluetooth, IEEE 802.15.14 and ZigBee.
"During the past 2 years, the ZigBee Alliance has generated a huge amount of publicity for the concept of wireless devices," says Forbes. "ZigBee builds upon the IEEE 802.15.14 standard, which defines a short-range, low-power, low data rate wireless interface specifically designed for small devices that have limited power, CPU and memory resources."
"Prior to ZigBee, there were no standards or industry specifications which addressed the requirements of a wireless sensor and control networks," claims Bob Heile, chairman of the ZigBee Alliance (San Ramon, CA). "What was previously available were limited proprietary solutions that solved specific niche applications but could not provide the broad interconnected solution afforded by the ZigBee technology for the wide range of networks found in the home, commercial and industrial space.
"The closest standard out there is Bluetooth, and that falls far short of the performance required for these networks on a number of fronts. Battery life and network size are at the top of the list with cost and complexity not far behind."
According to Heile, the battery life for Bluetooth devices is short, often following the mobile phone recharge model. He also claims that Bluetooth requires constant synchronization to stay running, which results in short battery life.
However, some observers question how effective ZigBee is for industrial applications. They point out that much of the focus has been on home automation applications, which have different needs from assembly lines.
"The low-end devices chosen as targets for ZigBee standardization leaves the current technology with several weaknesses when applied to industrial applications," warns Forbes. "Requirements for very high network reliability, long service life and large numbers of battery-powered nodes are outside of ZigBee's sweet spot."