Striking a balance for plantwide wireless

• By Shuji Yamamoto
• System Integration

Summary

Advantage of two industrial wireless technologies; one for operations and one for infrastructure

By Shuji Yamamoto 

Real life has a way of demonstrating that it is relatively rare to find a case where the phrase “one size fits all” truly applies. Many times, this assertion can be translated as “one size imposes compromises on all,” and so it is with industrial wireless networking. Several options are available, and engineers scrutinize the right combination of installed cost, connectivity, and power consumption to select the winner. However, in many cases choosing two winners may be the best answer.

A primary reason for moving to wireless sensors is to minimize installation cost, because home-run conduit and wire are removed from the equation. But even among wireless options, there are sustaining cost considerations, such as how often batteries need to be replaced.

Some industrial wireless standards, such as ISA100 Wireless, are already established wireless local area networks in many process plants for critical operations like monitoring and control of equipment, or even safety-related automation. This type of industrial wireless must have extremely high reliability and operate in a close to real-time manner for process control and safety applications.

By comparison, the use of Internet of Things (IoT) and Industrial IoT (IIoT) devices throughout facilities is quickly expanding for monitoring and even controlling noncritical infrastructure relating to maintenance and environmental management. For these types of applications, there are many reasons to select a protocol within a networking class known as low-power, wide-area (LPWA) networking. A prominent protocol in this area is LoRaWAN.

Implementing LPWA for IIoT devices in conjunction with a protocol like ISA100 Wireless for process devices lets end users strike an optimal balance between price and performance to achieve advanced, efficient, and safe plant operations. This article examines why LPWA is a compelling choice within a sitewide wireless network architecture for implementing IIoT devices.

Operations and infrastructure overlaps and gaps

When designing or expanding sitewide wireless network architectures, users must categorize the desired service for various field devices. Typical plant or factory wireless needs can be roughly divided into one of four types: safety, operation, maintenance, and environment (figure 1). The first two are considered operational, while the last two are infrastructure related.

Safety is usually considered the most critical application, followed closely by operation. Maintenance and environmental monitoring are most likely somewhat less critical, but important, nonetheless. With this in mind, wireless networking technologies should be selected based on these roles.

To do this, it is helpful to review some specific requirements for operational networks in comparison with infrastructure networks. Weighing these requirements drives the network technology selection, since sometimes the choices are gray rather than black or white. For instance, some characteristics such as "reliability" are always desirable. However, high reliability may be crucial in some applications, while lesser reliability may be acceptable in others.

Operational networks, such as ISA100 Wireless, must directly operate process devices and safety systems. Therefore, these networks are expected to deliver:

• real-time monitoring and command with less than 1-second response
• high reliability of communication infrastructure
• high integrity of data transmission
• excellent security
• medium-range communication
• flexible topologies (redundancy, backbone, mesh, star)
• coexistence with wired systems
• robustness within typical industrial environments

Infrastructure LPWA networks, on the other hand, typically monitor equipment and the environment. Therefore, these networks are expected to have:

• wide-area coverage, kilometers or tens of kilometers
• ultra-multipoint connections, up to 1,000 or even 10,000 points
• variable communication cycles ranging from 60 seconds to 60 minutes to three days
• easy physical installation to minimize field costs
• a possibility for data sharing by multiple top-level systems
• a focus on long-term data as opposed to instantaneous values
• suitability for use in multiple operating conditions
• relatively low cost per point

Based on the listed criteria, almost any conceivable field device can be logically categorized. Setting aside cost and technical details, a significant deciding issue is the poll time required for a signal. Operational devices are associated with immediacy and quick action, while infrastructure devices are often trended over a much longer time base.

A closer look at wireless networking technologies reveals why different types are best suited for certain roles.

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Power struggle

One consistent and common-sense bottom line when evaluating wireless technologies is the trade-off between power consumption and range (figure 2). Common consumer Wi-Fi is a large power consumer with relatively short range, although it delivers massive bandwidth. Low-power networks like Zigbee are finding a place in home automation scenarios, but their extremely low range limits them to personal area network applications. Industrial wireless networking such as ISA100 Wireless occupies a balanced region somewhere in the middle.

This leaves LPWA residing by itself in the low-power, wide-area position indicated by its name. For IIoT implementations, this is the sweet spot for two main reasons. The first is that low-power enables IIoT devices to be operated with just batteries, only needing replacement after years of service. No additional local power conduit and wire, or a local power source such as solar cells, are required, making these devices very convenient for hard-to-reach locations. The power constraint is not about saving power strictly for consumption costs, it is instead about enabling the device to be installed as a truly wireless physical island requiring minimal maintenance.

The second reason is that IIoT devices tend to be widely scattered around a site, so long-range communications are necessary. This also means it is far easier to add future sensors as funding allows without requiring additional components.

At the end of the day, power consumption, range, and the resulting available bandwidth determine where an industrial wireless network technology fits best.

Conventional industrial wireless network efforts were originally focused around supporting the operational type of applications, mostly due to the available underlying technologies at the time. To achieve sufficient performance that results in responsive control (action time less than about 1 second), the design of operational wireless networks is necessarily more heavily engineered up front.

Sometimes this involves specifying redundancy options. In cases where operational wireless networks are used in conjunction with classically wired systems, a well-engineered system will handle the two similarly, although of course they would be distinguishable.

There are ways to leverage operational wireless networking to monitor infrastructure-type signals, but the end user would be overpaying for hardware and design efforts every step of the way. Instead, it makes more sense to select a networking technology targeted for infrastructure applications.

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Focused on infrastructure

Contemporary LPWA networks have become available as the core technologies have improved, often based on consumer electronics breakthroughs. Advances in reduced power consumption (such as with handheld devices and consumer Bluetooth wireless) and maximized wireless network bandwidth have translated into similar benefits for industrial applications.

LPWA implementations, such as LoRaWAN, have now reached a practical level where they can be used to integrate thousands of sensors at a site. Additionally, LPWA is extensible beyond an on-premises solution to connect over the cloud, which effectively makes the transmission distance unlimited as long as Internet access is available.

It is worth noting that 3G/4G/5G mobile networking systems are a form of LPWA but are not considered here for industrial networking use due to relatively high service provider costs. This is because they are more aligned as the backbone of commercial communication networks at this time, as opposed to being considered workable for general wireless sensor networks. Also, end users would likely be concerned about building their sensor networks on systems that make them beholden to outside network providers.

For these reasons, LPWA networks and small field devices are an excellent fit for infrastructure monitoring applications. They can easily be used to retrofit existing equipment with instrumentation to support preventive maintenance efforts, and they can minimize personnel exposure by being installed in areas that formally required operator rounds.

The data delivered by IIoT devices in a LoRaWAN system can be used by analytical applications in parallel with operational systems, or it can be cross-connected to operations (figure 3). Many times, IIoT data is processed offline and separately from live operational data, such as to determine when rotating equipment is experiencing increased temperatures or vibration and should undergo preventive maintenance.

When engineers have gained confidence in the IIoT platform, they may choose to use the information to proactively modify active control strategies. This overarching concept of using all available data to produce optimal actions is the ultimate goal of any completely connected industrial enterprise. Next, let's look at a typical application.

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Applying small sensors

IIoT sensors for infrastructure are generally small sensors, easily installed even in remote or difficult physical locations. This allows extremely granular installations, providing condition-based sensing exactly where needed, as opposed to a wired installation where it is more important to centralize devices to minimize the wired infrastructure installation effort.

This granular nature also makes wireless infrastructure monitoring systems very scalable. Users can initially install sensors anywhere to meet immediate needs, and then add more sensors later as funding allows or where experience proves valuable.

Figure 4 depicts a basic IIoT installation and integration. Numerous IIoT field devices are installed as needed in the field and report over a LoRaWAN system to a plug-and-play gateway. This gateway in turn transmits the field data up to an on-premises or cloud-based system, where the data becomes available to any higher-level host or supervisory system. In fact, the cloud connectivity also means there are options to publish the data directly to portable devices, so field personnel can monitor the data from anywhere, especially near the equipment.

Host systems could be one or more of the following: the operational control system, a database and trending package, analytical software, or possibly even a system offering advanced machine intelligence algorithms. IIoT systems provide just the kind of "big data" that analytical software needs to do its work. In fact, the cloud implementation means that applicable data from multiple sites can be aggregated to look for larger trends, or to compare the different facilities against each other.

Process controls have always been the domain of operational technology (OT) personnel, but infrastructure monitoring in recent years has often been dependent on information technology (IT) staff. Although IT staff are proficient at networking and databases, they are often less experienced with industrial concepts and the nature of time-series process data.

Implementing infrastructure condition monitoring with LPWA plug-and-play functionality puts the maintenance and environmental monitoring tasks squarely in the hands of OT personnel, who are best equipped to use it. This results in a far more efficient integration.

One other note is that some IIoT sensors offer near-field communications (NFC) wireless capability. This very short-range (just a few centimeters) wireless link is not useful for ongoing data transmission but does enable common smartphones to act as local configuration and monitoring tools for sensor status. This is yet another case where IIoT devices can save end users money.

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Just right wireless

Conventional industrial wireless operational networks, such as ISA100 Wireless, will continue to experience a growing presence in automation systems for high-performance control and monitoring. However, to truly take advantage of widespread IIoT advancements, it is important to adopt LPWA networking technology such as LoRaWAN to economically integrate multitudes of sensors on a sitewide basis.

LPWA is a just-right fit of cost, power consumption, range, and bandwidth for monitoring infrastructure conditions such as temperature and vibration. This data is key to preventative and predictive maintenance programs. The nature of LPWA devices means they are economical to install initially, since no wiring is required, and they are also cost effective on a long-term basis due to minimal maintenance requirements.

Operational and LPWA infrastructure wireless networking work especially well in conjunction with each other, because the combination covers such a wide range of wireless needs. Used together in a sitewide industrial wireless network, they deliver a comprehensive balance of immediate and proactive plant operations.

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