Bob Karschnia, VP of Wireless, Emerson Automation Solutions [NYSE: EMR]Industrial process plants have unique needs and requirements for their wireless infrastructure, making these networks very different from their commercial counterparts such as Wi-Fi and Bluetooth. Although these commercial networks have their place, particularly Wi-Fi which is often used for mobile worker applications in industrial facilities, a different type of wireless network is needed for Industrial Internet of Things (IIoT) installations.
The IIoT in process plants requires very reliable and consistent connectivity from hundreds or even thousands of sensors to host systems. The sensors measure plant operating parameters including temperature, pressure, level, flow, vibration and many others. This measurement data is sent via a wireless network to a host system where it’s converted to actionable information used to help plants increase uptime and throughput, reduce energy use, improve safety, and make other operational improvements.
Wireless networks in industrial facilities must overcome a host of challenges, most of which aren’t found in commercial and office installations. These challenges include:
• Deal with multiple obstructions in the form of equipment, metal buildings and structures, trucks, etc.
• Cover very large areas, up to a few square miles for mining operations or big chemical plants
• Operate for years without any maintenance, often in very harsh outdoor environments
• Deliver data at consistent update rates regardless of network loading
"Industrial wireless networks require stable update rates, defined as how often a sensor transmits data to a gateway"
Decades of research and real-world application experience have shown the best way to meet these challenges is with a self-organizing and self-healing mesh network, such as WirelessHART™ (Figure). These IIoT mesh networks connect a number of wireless sensors to a gateway, and the gateway is then hardwired to the plant’s networking infrastructure. Each wireless sensor can act as a repeater, allowing the network to automatically and continuously select the best communication path to the gateway.
Larger installations require multiple gateways as each gateway can accommodate about 100 sensors. In these installations, each gateway communicates with the main gateway via the wireless network, with only the main gateway hardwired to the control and monitoring systems.
Although a mesh network inherently handles obstructions by creating multiple communication paths among sensors and the corresponding gateway and dynamically selecting the best route, it does not have a particularly long communication range. But when communications do need to span longer distances, over about 300m, there are two ways to address the issue. The first is by adding repeaters, either in the form of sensors or dedicated repeaters. The second is to use a powered antenna.
Another big difference between industrial and commercial wireless networks is required uptime. The ability to run for years without maintenance is critical for industrial facilities as many operate 24/7/365, with maintenance shutdowns typically scheduled years apart. This requirement is made even more difficult by the harsh environments often found in industrial plants where wide temperature swings, heavy vibration, corrosive atmospheres, and other adverse conditions are common.
The wireless sensors, gateways and antennas must be able to operate for years in these environments without any required maintenance. Gateways are connected to the plant power system, but sensors often are not, and therefore must provide their own operating power for years.
This is done by equipping each wireless sensor with a specially designed power module, consisting of a battery and ancillary components. The power module allows the sensor to operate for up to 10 years with no maintenance, depending on update rates. Power modules are also available with energy scavenging, which allows the module to harvest energy from ambient conditions such as heat and vibration, permitting operation for decades.
Update or communication rates are another area where industrial and commercial wireless networks differ. The communication rates of most commercial wireless networks slow significantly as more users join the network, and as users load the network with more traffic. This can slow the network to the point where use is impractical.
Industrial wireless networks require stable update rates, defined as how often a sensor transmits data to a gateway. Typical update rates for sensors range from one to thirty seconds, and the update rate at each sensor can be set individually. Once set, the update rate will be stable regardless of network loading, although design modifications may be required as the number of sensors grows, which typically consist of adding more gateways.
Once a WirelessHART™ or other industrial mesh network is installed, plants and facilities can begin to realize the operational benefits of the IIoT. The initial wireless network installation requires careful design, planning and training—a process simplified by working with experienced suppliers. Once the network is installed, adding new sensors is quick, easy and inexpensive, so plants can quickly expand their IIoT installations to meet new operational challenges.
Industrial wireless networks face many challenges typically not found with commercial installations, but WirelessHART™ and other industrial wireless mesh networks were designed from the ground up to address these issues. This allows their use in the harsh environments found in industrial plants and facilities with the required performance, reliability and longevity.
