The proliferation of wireless networks in industrial plants and facilities has provided substantial benefits to end users in the form of improved operations, but has also raised some potential issues. Fortunately, these can be addressed by correct network design, aided by software-based tools. These tools help users design networks correctly, monitor networks through their lifecycle, and troubleshoot problems.
Although this column will focus on WirelessHART®, the world’s leading industrial wireless network for industrial IoT applications, many of the principles espoused are applicable to other types of wireless RF networks used in industrial plants and facilities.
WirelessHART is supported by dozens of vendors and administered by the independent FieldComm Group organization (https://fieldcommgroup.org/). Emerson alone has installed over 30,000 WirelessHART networks, with more than 10 billion hours or operation.
WirelessHART networks consist of several transmitters which measure process parameters such as pressure, level, temperature, flow, etc. Each of these transmitters communicates to one or more gateways through a wireless mesh network. One or more gateways are connected to control and monitoring systems through a hardwired digital data link, usually serial Modbus or Ethernet.
Design for Success
The most important step in managing any network, wired or wireless, is designing it correctly up front. A poorly designed network will present a host of challenges throughout its lifecycle as users try to correct errors made in initial design. On the other hand, a well-designed network will require minimal maintenance, with most issues due to changes in the network or its surroundings. These issues are usually easy to address for a well-designed network, but extremely difficult if errors were made in initial design.
There are three key steps when designing a wireless device network:
- Scope – Determine the method to distribute WirelessHART gateways across the site. This can either be on a geographic and spatial basis, or more commonly driven by the logical arrangement of the plant; i.e. by process area or unit.
- Design – Apply design rules to ensure optimum connectivity of field devices back to the WirelessHART Gateway.
- Fortify – Use tools to identify and correct any potential weaknesses in the network design.
A wireless mesh network gets its reliability from multiple communication pathways, so ensuring each device has multiple neighbors within range will result in the most dependable network. To achieve this, a minimum of five wireless devices should be within effective range of each gateway. Each wireless device in the network should have a minimum of three other devices with potential communication paths.
Below are three basic classifications for calculating effective range in industrial plants and facilities:
- Heavy Obstruction – Range of 100 feet. This is the typical heavy density plant environment.
- Medium Obstruction – Range of 250 feet. This is an area with less density, with lots of space between equipment and infrastructure.
- Light Obstruction – Range of 500 feet. Typical of tank farms. Despite tanks being large obstructions, there is typically lots of space between, which makes for good RF propagation.
Planning tools are available to assist with these network designs, such as Emerson’s AMS Wireless SNAP-ON application (Figure). This application allows users to upload a plot plan of the plant, and then design the wireless network for the designated area. The application can then check proposed designs against industry best practices.
Once the wireless network is designed, the application can monitor the network after installation to ensure correct ongoing operation. This monitoring includes troubleshooting tools driven by graphical displays and predictive network diagnostics, and reports of key network operating parameters. Using the software, network performance can be monitored and maintained by balancing wireless network usage and gateway capacity.
If an issue can’t be solved using the network management application, some suppliers offer a service whereby network operating data can be captured by the gateway and emailed to the supplier for detailed analysis, followed by recommendations to resolve the issue.
Emerson’s wireless planning tool, or a similar tool from another supplier, can be used to verify the wireless network complies with basic design and range rules. If any issues are detected, solutions to strengthen designs include:
- Adding repeaters, which are simply wireless devices used as reinforcing radios in the network.
- Placing gateways in locations that maximize connections within the network. Working with the application administrator to identify all potential gateway integration points is a useful process to determine optimal gateway locations.
Planning tools can also be used to stress test the network and identify weak spots. This can be done by reducing the effective range against which all the design recommendations are tested. This process builds confidence in the design.
References 1 and 2 go into much more detail regarding network design.
Once a wireless network is installed, it’s important to provide proper cybersecurity. IIoT wireless cybersecurity must be addressed upfront, starting with selection of a network with the required security features. Once the proper network is selected, users must be vigilant to ensure ongoing cybersecurity. If these steps are taken, the network will be sufficiently secure for the most critical applications. See Reference 3 for more detail on this subject.
Wireless networks are becoming more widespread in industrial plants and facilities. Correct initial design of these networks is critical for reliable operation, and automation software-based tools exist to aid in these efforts.
automation.com Oct 2015, Wireless Device Network Planning and Design, Moazzam Shamsi: http://www.automation.com/automation-news/todays-featured-news-headlines/wireless-device-network-planning-and-design
System Engineering Guidelines, IEC 62591 WirelessHART: http://www.emerson.com/documents/automation/79900.pdf
CiO Story Aug 2017, IIoT Wireless Cybersecurity, Bob Karschnia: http://ciostory.com/technology/security/iiot-wireless-cybersecurity/