Industrial wireless selection and implementation
Industrial wireless networks require a lot of planning and preparation because there are many elements that can hamper or interfere with manufacturing operations.
Industrial environments have many common attributes: they are dirty, electrically noisy, and present many obstructions or disruptions to RF propagation. The use of consumer-grade wireless equipment will not work in the long term. Equipment must be tailored to the environment in which it will operate – industrial installations do not follow the standard rules of design. Field surveys are useful, but the presence of electrical noise and moving equipment, large metal structures or even the presence of water in an industrial process will have a large impact on signal propagation.
Industrial wireless access points
An industrial installation requires more wireless access points than an office installation because of the presence of numerous signal disrupters. The use of directional antennas also could become a necessity because of the topology of the industrial facility. A warehouse, for instance, requires directional antennas be used to direct radio frequency (RF) down narrow aisles between metal shelving, likely filled with metal or some material that will absorb RF.
A machine shop is full of motors and moving objects such as forklifts and overhead cranes. Some manufacturing equipment requires liquid coolants that create vapors, sprays or splashing that can disrupt propagation or cover the wireless equipment in grease or water. Some processes require arc welding, which produces a powerful broad-spectrum noise signature that can disrupt many RF signals.
The first parameter to consider is the working environment. Considering the above, the most obvious concern is the equipment enclosure. Choosing the correct enclosure is the first and most basic specification and protects the access point from being damaged by environmental factors.
Industrial enclosures as defined by NEMA or using the IP classification system simplifies the design specification, but it will require the specific area in which the equipment is to be installed be classified by the facility engineering section. Guessing at proper enclosure is not the proper approach and will lead to early and unexpected failures of the system. All industrial environments are different and need to be assessed on a case-by-case basis.
Another option is to place the wireless equipment outside of the harsh environment and install a distributed antenna system (DAS) to provide RF to the needed areas; however, this is often not practical and will add significant cost to the installation. DAS requires a through understanding of signal propagation through the DAS and operates through a system of cabling and directional signal splitters or couplers, the design of which can be daunting.
A single antenna driven by a single access point is another option, but it requires multiple access points be used across the facility at each controlled process. This can be a good option for small shops, but will be a problem for larger shops. A DAS is economical in that one transmitter can drive multiple antennas, but care must be taken to ensure that adequate power is available for the DAS. The principle attenuation factors are the cable (by length) and the directional splitters, which by nature present directional attenuation.
Antennas are a crucial factor in the design of an industrial wireless network. In an office environment, simple dipole antennas, such as those on a home wireless router, are sufficient for providing propagation to the area. Taking one example, such as a warehouse environment, we can see where the selection and placement of the proper antenna is essential to the reliable operation of the network. Aside from considerations of bandwidth and capacity, propagation is the major consideration here.
Warehouses have large storage shelving with long aisles and moving equipment. Inventory on the shelves will absorb and reflect RF depending upon material; a water bottling facility, for example, may have pallets full of bottled water stored on metal shelves. This is a worst-case scenario because the water in the bottles will attenuate the signal while the metal shelving will reflect it. Moving equipment, like forklifts or stock pickers, can have wireless devices on board. However, a common reception problem is caused by the metal cage protecting the operator. The metal cage can severely attenuate the RF signal; an antenna external to the cage is recommended for best performance. Industrially-hardened access points are expensive, but they are designed for use in these applications and will get the job done.
Directional antennas come in several configurations, the most important parameters being beam width and amplification. Beam width is the angle of the RF propagation from the antenna and is shown on a polar chart. The beam width of a Yagi antenna, for example, is narrow and directional in the direction of transmission; this is measured at the -3dB points on the polar chart.
Amplification determines the distance the signal will propagate for a given frequency. Directional antennas also serve to avoid sources of attenuation or disruption by focusing RF on a specific area, and, being as antenna performance is reciprocal, signal reception from the focused area also will improve and inherently reject surrounding sources of electromagnetic interference (EMI).
Both factors can be used to determine the proper antenna for the application. Bar code readers require a stable and continuous connection to properly transmit the inventory information back to the facility’s servers. To avoid bandwith issues, a general rule of thumb is installing directional antennas at each end of the aisle to ensure that the entire length of the aisle has adequate coverage and gradually adjust power levels to provide well defined cones of propagation without creating interference. This is an oversimplification, however, because all facilities differ in configuration and inventory.
Electrical noise’s impact on the signal
In a manufacturing environment, electrical noise and moving equipment are the chief disruptors to the propagated signal. Using wireless technology to monitor and control equipment is very forward thinking and disruptive in a social sense. Entire facilities can be operated unmanned as is being done with wired networking technology, wireless technology offers more flexibility in equipment placement and lower implementation costs.
Electrical noise, depending on the frequency used, will have a greater or lesser effect on signal disruption. At the higher frequencies (GHz), EMI will have a negligible effect unless the noise is the result of wide-band noise generators, like arc generating equipment, which generate EMI in a very wide spectrum.
Lower frequency bands (VHF and UHF) are more susceptible to noise generated by motors, solenoids and the like, and the harmonics generated. Shielding bad offenders is a technique that works in isolated cases. A room full of arc welders or variable frequency drive (VFD) motors can wreak havoc on wired and wireless networks if proper separation is not observed. Other equipment, such as line reactors, can and will magnetically couple to antenna cabling and cause real damage to transmitting equipment. Speak to a wireless integrator about how their equipment deals with noise and their methods of noise rejection.
Proper placement of the access point or antenna, such as above a manufacturing area containing controlled or monitored equipment, will focus the RF onto that area. This placement will avoid interference of reflection of signals from forklifts or other equipment. Of course, placement of the access point (AP) local to the equipment is a good option and avoids cabling costs. For crucial processes, a Faraday Cage can be placed around the processing area (or the source of EMI), along with the wireless access point.
The area would be electromagnetically isolated from the surrounding facility and wireless connectivity would be stable and continuous. This is an expensive option, however, and would only be used for crucial processes and where conventional network cabling is not practical.
Pre-implementation facility surveys for industrial situations do not follow the rules for office surveys. In an office survey, the object is to provide coverage and capacity, while identifying areas and sources of attenuation, such as concrete elevator shafts and microwave ovens. Illegal, or rogue APs are also a primary reason for primary and follow-up surveys. Industrial site surveys are focused on coverage and capacity, but also identifying potential sources of EMI, which can result in signal disruption, periodic disruptions and reflections from moving equipment, and process-specific materials, liquids and processing equipment movements must also be identified in order to design around them.
Care should be taken to separate the industrial wireless network from the corporate network. Cybersecurity and proper cyberhygiene are essential parts of the overall system design. The use of a robust firewall to provide controlled access will allow authorized personnel to upgrade equipment or load new programming into machine tools or scanners.
An intrusion detection system (IDS), whether integrated or overlay, is a good investment for an automated or networked facility. Layers of defense based on training, equipment selection, and monitoring will provide adequate protection of the facility from attack. However, this is not a substitute for surveillance and vigilance.
As wireless technology becomes more robust and inexpensive, its use will become more prevalent. The elimination of wiring affords great opportunities: flexibility, efficiency, improved bottom line — these are all possible using a wireless network. Machinery or production equipment can be moved without worrying about network cabling and can be grouped in more efficient, space savings ways.
A robust and stable wireless network can be installed and operated in an otherwise hostile environment based upon a properly conducted survey with informed design decisions. Using a trained and certified wireless professional is essential from the standpoint of reliability and liability. Disruption of a vital process can result in a large and unexpected expense and material loss. Taking the time to thoroughly understand the industrial environment and properly matching wireless equipment to that environment is the formula for a successful implementation.
Daniel E. Capano is senior project manager, Gannett Fleming Engineers and Architects, and on the Control Engineering Editorial Advisory Board. Edited by Chris Vavra, associate editor, Control Engineering, CFE Media and Technology, firstname.lastname@example.org.
KEYWORDS: Cybersecurity, industrial networking, radio frequency (RF)
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