Evaluating IoT wireless protocols for industrial applications
Do IoT-based wireless technologies designed for municipal, building, and residential sensor networks offer anything for industrial users? How about 5G?
- Developing a wireless protocol for process instrumentation applications is a time-consuming and expensive undertaking.
- Technologies emerging from the Internet of Things (IoT) are being promoted as ways to connect industrial and building automation sensors.
- There is no single wireless protocol that solves all application problems and that will continue even in the 5G era.
When approaching technical evaluations, engineers must compare tradeoffs, such as weighing pros and cons of a Coriolis versus an ultrasonic flowmeter for a specific application, if a wired or wireless communication should be used, or what kind of wireless protocols to use. When making these types of comparisons, few situations are more complex than industrial wireless protocols due to the factors involved and the many possibilities.
Looking at the list of industrial wireless protocols, each is optimized in a specific way to balance interacting characteristics. These include:
- Power consumption: Wireless functions require power, but adding capabilities increases overall consumption, which reduces battery life.
- Bandwidth: Sending small amounts of data, such as a single process variable, is much easier to design and implement since increasing bandwidth increases power consumption.
- Update rate: How often must the device send its data? Once per day or six times per minute? Multiply sending frequency times bandwidth for total power consumption.
- Distance: Increasing transmission distance calls for more power, but can be helped with effective antenna design and placement.
- Bidirectionality: A device that only transmits data is simpler to design and less power hungry, but lacks many useful capabilities.
- Reliability: Critical data requires a mechanism to verify a transmission with a return acknowledgment. Otherwise, it must send the data again until it is successful.
- Security: Only the intended recipient should be able to understand the data.
Operation for an industrial wireless device is further complicated by its fixed location. Both ends of a communication are locked in place and can’t move around the side of the building for better reception.
Specific use case examples
Consider two functional extremes: a smartphone and a water-meter reporting device. The smartphone has every function imaginable: It’s bidirectional, has multiple radios and can handle large amounts of data, but its reliability is low. Calls get dropped and downloading a file can be hit-or-miss. It’s up to the user to try again. A smartphone also has very short battery life.
The water-meter reporting device sends a very small packet of data, maybe only once a month, so the battery can last 10 years. It has no bidirectional capability so if the receiving system misses a transmission, it can try again tomorrow.
Industrial applications fall somewhere between these two extremes and need to find the right balance.
Optimized for field devices
For more than 13 years, WirelessHART (adopted by the International Electrotechnical Commission as IEC 62591) has served industrial users as the most widely deployed wireless protocol for process instrumentation, actuators and other advanced field devices (Figure 1). It optimizes the tradeoffs discussed for this specific and critical application.
WirelessHART is a secure, multi-vendor, interoperable wireless standard designed to provide highly reliable, low latency connectivity for process monitoring and automation applications.
WirelessHART uses IEEE 802.15.4 radio technology with deterministic scheduling, plus frequency, temporal, and path diversity to achieve reliable, deterministic data transport using very little power. WirelessHART instruments have an expected 10-year battery life with update periods of 30 seconds and also supports low-latency downstream communications without sacrificing battery life, and it works with most existing handheld field devices to support calibration and diagnostics in the field.
Its range is relatively short, but its self-organizing mesh technology can pass messages from one instrument to another, or via a repeater, to cover long distances or circumvent network disruptions. The network’s short range and low bandwidth extend battery life, even with frequent updates. The battery can also power a sensor, such as for measuring pressure or temperature, that likewise has low power consumption. This makes it possible to manufacture pressure, temperature and other transmitters as native instruments in a single unit, requiring no external wiring of any kind. Any HART-enabled instrument can be converted to WirelessHART by adding an adapter (Figure 2).
The number of WirelessHART instruments has grown over the years, extending the catalog of process instruments and basic analyzers.
Extending applications and markets for wireless protocols
Developing a wireless protocol and going through all the approval procedures is a time-consuming and expensive undertaking. Developers often explore other possible applications and customers before moving into the world of industrial instrumentation.
Some of the more complex process analyzers create large amounts of data and use industrial Ethernet or Wi-Fi outputs, but their energy consumption is not suitable for battery power. The idea of extending an internet connection and an IP address to large populations of individual instruments hasn’t caught on, either.
Extending IoT networks
Technologies emerging from the Internet of Things (IoT), such as LoRaWAN, are being promoted as ways to connect industrial, building automation and even residential sensors in a wide variety of applications (Figure 3).
The LoRa Alliance describes the protocol: “LoRaWAN network architecture is deployed in a star-of-stars topology in which gateways relay messages between end-devices and a central network server. The gateways are connected to the network server via standard IP connections and act as a transparent bridge, simply converting RF packets to IP packets and vice versa. The wireless communication takes advantage of the long-range characteristics of the LoRa physical layer, allowing a single-hop link between the end-device and one or many gateways. All modes are capable of bi-directional communication, and there is support for multicast addressing groups to make efficient use of spectrum during tasks such as firmware over-the-air upgrades or other mass distribution messages.”
A handful of industrial LoRaWAN devices have come onto the market with a range of one mile. That coverage, however, comes at the expense of battery life with the devices promising just four years, even with an update rate of one hour. The long update rate limits this approach to monitoring of very slow moving process variables.
5G application beyond smartphones
The latest generation of cellular connectivity, 5G, is reaching into the industrial world. Most general discussion centers on enhanced mobile broadband (eMBB) for smartphones and tablets, with major improvement as compared to 4G for virtual reality media and UltraHD video. eMBB supports data rates up to 20 Gbps with up to 10,000 times higher traffic than 4G systems.
Two other areas have drawn industrial users’ attention:
- Ultra-reliable low-latency communications (URLLC) provides support for critical systems requiring extremely low latency, such as self-driving vehicles and machine control. URLLC offers transport latency of less than 1 ms with data rates up to 10 Mbps. Like eMBB, URLLC relies on the use of the 5G New Radio (5G NR).
- Massive machine-type communication (mMTC) supports machine-to-machine communication with data rates up to 100 kbps. mMTC applications include municipal metering and smart city deployments where extremely low data rates (e.g., once per day or less) and high latency are acceptable.
Suitable for instrumentation, process networks?
Is there reason to expect 5G or LoRaWAN wireless process networks supplanting WirelessHART or other industrial instrument networks, primarily ISA 100? Anything is possible, but so far, nothing indicates WirelessHART has reached its technical limits, or that the newer offerings have leaped ahead with useful functionality. The sophistication of advanced instrumentation continues to improve and WirelessHART has kept pace.
Options for backhaul
WirelessHART instruments and field devices send their data to a gateway which passes the data on to an automation host system (for process instruments) or the maintenance department (for asset health monitoring). In most typical process plant environments, these connections are via Modbus or industrial Ethernet.
In a large facility, such as a refinery, multiple networks may operate in parallel, potentially one or more for each production unit, resulting in many gateways. In such situations, the plant’s wired Ethernet networks may need to be extended, or gateways can interface with a Wi-Fi router, passing accumulated data along to the places that need it.
This is simple enough, but WirelessHART’s versatility allows it to be installed in a wide variety of applications outside of typical plants. For example, a remote oil or gas wellsite (Figure 4), pipeline compressor station, or similar installation might have a dozen or more WirelessHART instruments. How does data get from the gateway to the systems and people who need it? There have been various options from satellites to cellular over the years.
5G looks like it offers possibilities to provide this critical backhaul function for individual plants or remote locations, enabling short- or long-range transmission of WirelessHART data to the cloud or a private network (Figure 5).
Numerous gateways are already connected to cellular modems, enabling operational process monitoring and control, plus remote predictive maintenance of critical plant assets. 5G will improve this existing capability.
Proven performance and availability
A new technology can’t be viable in the marketplace until vendors are convinced there is sufficient customer demand to justify investing in product development. WirelessHART had to prove its technical capabilities before vendors would take the next steps and begin filling the product pipeline.
Process manufacturers are generally conservative, but gradually became convinced of WirelessHART’s reliability and started adopting it, a bit at a time initially, but then more broadly. This quickly launched an upward spiral of growing numbers of networks and devices—driving development of more devices, more vendors, more network management tools, and more satisfied users.
Today, with more than 45,000 networks in operation connected to millions of individual devices from a wide variety of vendors, WirelessHART is a mature technology, but it is still growing.
Neither 5G cellular nor LoRaWAN instrumentation is likely to replace WirelessHART instrumentation for typical industrial process automation applications in the foreseeable future. In fact, the outlook for HART and WirelessHART instrumentation remains strong as input/output (I/O) densities continue to increase with the size and complexity of new and existing facilities. Users appreciate its low-latency downstream communications, long battery life and the ability to work with most existing handheld field devices to support calibration and diagnostics in the field.
In today’s industrial environment, no wireless protocol can solve all applications. Many equipment vendors and end user companies are looking forward to the coexistence industrial protocols such as WirelessHART with 5G and possibly other wireless protocols, working together to transform the future of global industry.
Keywords: WirelessHART, process instrumentation, field instrumentation
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