How wireless networks are changing industrial environments
Wireless networks are transforming industrial plants and manufacturing operations globally. Based on the standard IEEE 802.15.4, this evolution from wired to wireless networks in industrial, manufacturing, and warehousing applications is primarily driven by the need to reduce costs, improve uptime, save energy, and improve workplace safety.
Those working in warehouses, factories, and industrial facilities are discovering that wireless networks can greatly reduce network installation and maintenance expenses. Because IEEE 802.15.4 wireless can transmit data throughout a plant, penetrating walls and floors, it eliminates wiring costs and cable routing problems, while placing fewer restrictions on the location and placement of equipment.
It’s also faster to install, which is another factor behind the move to wireless, particularly for factory floors that need to reconfigure manufacturing and assembly lines quickly and efficiently to ensure a minimal amount of downtime.
By using wireless to reconfigure or change the physical layout of an assembly line, the plant manager can simply move the machines to new locations and turn on the wireless network, eliminating the need to re-route or install cables.
Maintenance and repair costs are another challenge for plant managers that can be reduced by using wireless communications instead of cabling.
Switches play an essential role in industrial and transportation controls, monitoring the position and presence of doors, booms, and valves. However, wired switches and sensors are often a challenge to install and maintain, particularly in harsh environments or where wiring flexes frequently. In addition, traditional wires can cause tripping hazards or get damaged during normal equipment operation, thus causing expensive downtime.
Wireless switches help reduce maintenance costs because the equipment connections are less complex. By eliminating cabling for sensors and switches, plant managers can simplify troubleshooting. In some cases, using battery-powered switches and sensors removes the need to use any cables at all. Wireless networks also increase system reliability by eliminating the potential for continuity issues caused by wiring or connectors.
Additionally, wireless devices are simpler to replace or reconfigure. For example, there is no need to disconnect and re-attach wiring, which also eliminates the risk of incorrect wire attachment. In many cases, the installation of a new wireless network is less expensive and faster than replacing the existing damaged wire, which takes time to troubleshoot and replace, causing considerable downtime.
Wireless is not just for inside the factory. Wireless is often the best networking technology for outdoor applications, such as shipping centers, warehouse yards, lumberyards, airports, fueling stations, and more. This is especially true in large, open locations where underground cables are at constant risk from harsh environmental elements as well as the travel of heavy vehicles across them. It can take weeks to troubleshoot and repair a broken cable under a large driveway. In contrast, replacing it with a wired network may take hours and is much less expensive.
Industrial wireless backbone
The IEEE 802.15.4 standard is a robust wireless personal area network (PAN) that is specifically targeted toward the low-power, low-bandwidth networks commonly used in industrial monitoring and control.
Here’s how it works: an IEEE 802.15.4 transceiver integrated with an industrial switch or sensor communicates to a monitoring receiver that can handle multiple switches in a star-configuration network. Every network, and each wireless device in the network, has a unique identification number that allows the device and its associated monitor to encode their signals. This ensures that the communications link between them is private and virtually immune to crosstalk from other switches or networks.
These 802.15.4 radios provide reliable connectivity in large indoor open spaces and/or outdoor installations with a relatively open line-of-sight between device and monitor. A 35-dB link margin ensures that minor obstacles or even heavy precipitation will not compromise communications. In some installations and depending on materials, the signal can penetrate intervening walls. This also prevents temporary outages when a truck or other mobile piece of equipment is moved between the sensors and the receiver.
The allowable operating range of an IEEE 802.15.4 radio is greater than 1000 ft (304 m). In extreme conditions such as heavy precipitation, the signal could be reduced by approximately 75 ft (23 m).
Because 802.15.4 devices draw so little power, they can be operated by industry-standard batteries, for reliable operation and varied installation options. They also eliminate the need for situation-dependent, unreliable, and expensive energy scavenging. A wireless sensor or switch may operate for several years without a battery replacement or re-charging, depending on the design.
Typically, the monitor/receiver unit in a wireless network can support either one device or multiple devices. For example, one receiver can support up to 14 remote battery-powered wireless devices. The controller can monitor sensor and switch status, signal strength, and battery levels for each device on its network. If a battery starts to die, or a switch gets blocked, the operator will know instantly and can take corrective measures.
Wireless on/off controllers are also available. Powered by batteries, these wireless operator interface devices can be located for easy operational access without spending a lot of time to connect them to the control network or to a power source.
More wireless industrial photos and links follow on the next page, including information on wireless interference, security, and flexibility.
No interference, security
Because IEEE 802.15.4 is a PAN standard, it operates independently of other common wireless LAN technologies such as Bluetooth, Wi-Fi, and cordless phones. Even though they may be operating in the same 2.4 Ghz spectrum range, this means there is no exchange of information or other interaction between a PAN and the LAN, eliminating the need for corporate IT department involvement.
To ensure secure communications links, IEEE 802.15.4 radios can be set up to require registration with their network monitors. This registration or “pairing” process takes less than five seconds and needs to be performed only once to establish the linkage. Once a device and its monitor have been paired, the two exchange information as long as both have power.
IEEE 802.15.4 security techniques are part of the pairing process. When registration is activated, the monitor provides the switch with several pieces of information. The first is the monitor’s individual 16-bit network identification number, which the monitor selects at power-up to avoid conflict with other networks in the vicinity. The second is a unique 16-bit address for the wireless devices, which the monitor creates. The third piece of data is a 128-bit encryption key that the pair will use to encode future communications. Once the information is exchanged, the switch and monitor use it to address and encode the signals they exchange.
Once established, the pairing is maintained even if the monitor loses power or a battery is replaced in the switch. This ensures a self-healing network and simplifies system maintenance. The monitor can automatically re-establish any dropped link to a registered switch. Replacement or reconfiguration of the devices is performed through a clearing and repairing process.
The combination of addressing and encryption helps to ensure the uniqueness and security of each wireless device’s channel. No two monitors or switches will have the same network address, so the monitors and the sensors/switches will not respond to signals originating from other networks. This means a monitor will not confuse signals within its network, and switches will not respond to signals intended for other switches.
Even if an addressing error occurs somewhere, the network will not react to the erroneous signal because the encryption keys for decoding the message will not match. The use of encryption further ensures that no unregistered node can successfully insert erroneous signals into a network or decode signals from a network, making the network secure from eavesdropping and hacking.
Less cost, greater flexibility
Using an 802.15.4 radio network to connect switches and sensors to a central controller frees industrial and manufacturing equipment developers and users from many of the costs and restrictions of wired solutions. It also expands the range of possible uses and placement of monitoring devices, making it easier and faster to reconfigure the factory floor for new product designs. As a result, the commissioning and lifetime cost of the network drops, while significantly increasing reliability and integrity.
When plant managers evaluate the advantages and drawbacks of wired versus wireless networks, they need to consider cost savings, maintenance issues, ease of installation and configurability, uptime, and security. In many cases, installing a new wireless network is less expensive in hard costs and installation time than trying to replace a faulty or existing wired network. IEEE 802.15.4 based wireless networks have proven themselves reliable, robust, and cost effective for a wide range of industrial, warehousing, and facility applications.
– Todd Hanson is with Honeywell Sensing and Control (S&C). Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering, Plant Engineering, and Consulting-Specifying Engineer, firstname.lastname@example.org.