Industrial wireless instrumentation is rapidly becoming the technology of choice for a growing class of applications. A wireless deployment saves significant costs compared to an equivalent wired installation, resulting in savings of 20 to 30 percent in simple configurations. Cost reductions can be even more compelling in scaled installations or in remote locations. Where wiring is cost prohibitive or infeasible, wireless enables best-practice instrumentation wherever it is needed for efficient and safe industrial operation.

The cost advantages of wireless instrumentation improve with scale. In a wired system, the cost of each additional instrument requires extra wiring and the associated labor, equipment, and maintenance. A wireless system, if designed for scalability, can accommodate additional devices with the same infrastructure and no additional wiring. For the first time, applications with hundreds or thousands of measurement points can be reasonably contemplated.

Until fairly recently, most users and experts viewed wireless instruments as intrinsically inferior to their wired counterparts, with wired instrumentation always being preferred when feasible. As experience with wireless technology grows, this attitude is shifting, with wireless becoming the default user selection for well-proven applications. Today, major users require cost justification for wired instrumentation in applications where wireless has been demonstrated to exceed user requirements.

Figure 1: Christensen innovation model adapted for industrial wireless

In Clayton Christensen’s model of innovation, adapted in figure 1, low-cost products initially take a beachhead position with simple applications at the lower end of a market. From that starting point, they work their way up-market. A tipping point occurs when mainstream users discover that the low-cost products can be used in high-end applications. Today, most major users are in the “mainstream adoption” zone, which is shown as an oval to indicate that adoption rates vary from user to user.

Wired versus wireless instrumentation

Major advantages of wireless instrumentation include:

• Lower cost, especially when large numbers of instruments are installed.
• Manageability. When wired connections fail, they are typically complete failures that occur without notice. Wireless failures are usually transient, and those transient problems can mostly be avoided by preventative maintenance linked to wireless diagnostics.
• Flexibility. After a wireless system is installed, it is easy to add new wireless instruments and also to report more data from existing instruments using wireless adapters.
• Security. Wireless security extends to the field instrument and does not rely on physical security of the transmission medium.
• Redundancy within a wireless network. Typically, wired instrumentation relies on a single wire to each instrument, with various opportunities for failure. Field experience demonstrates that a redundant wireless channel can be every bit as reliable as a nonredundant wired channel, particularly when wires are long or subjected to challenging conditions.
• Redundancy at the plant level. A wireless system can add redundancy to wired reporting, with the same data reported through wired and wireless channels. Similarly, when field instrumentation is involved in an independent protection layer (IPL), wireless may be an advantage if another IPL uses available wiring.

Disadvantages of battery-powered operation include:

• Battery maintenance. Maintaining the batteries of wireless devices somewhat offsets wireless cost savings. A well-designed wireless solution should ensure that battery replacement occurs in conjunction with an instrument’s general maintenance interval.
• Limited wireless instrumentation. An ISA100 Wireless adapter can convert a wide range of existing instruments to wireless, but only if the wired instrument has the power to operate. In locations where there is no source of external DC power, instrumentation options can be limited. New wireless products are being rapidly released to meet market demand.
• Continuous reporting. In some use cases, it is not technically feasible to sample and report process data continuously under battery power. ISA100 Wireless devices can be configured to report process data frequently in critical applications, with predictable battery life impacts, but only if the sensor has the energy to collect the data in the first place.

Disadvantages of radio operation include:

• Procedural barriers. Wired instruments have been used for decades, and processes for specifying and approving wired systems are well established at user sites. Many of these same users do not have clear processes for approving wireless, particularly when safety credit is involved.
• Statistical nature of radios. Radio performance is statistical by nature, with packet errors and retries being fundamental considerations for any wireless system design. A well-designed wireless system will have plenty of built-in margin, as well as extensive network diagnostics that detect loss of margin even while the system achieves its performance objectives.
• Limited reporting rates. ISA100 Wireless is designed to support reporting as frequently as every 0.25 seconds with a transmission latency of 0.10 seconds in structured configurations. Faster reporting rates are considered (by the major standards) unsuitable for battery-powered operation at this time.
• Spectrum management. Wireless instrumentation shares the radio spectrum with other systems and applications. Spectrum management generally needs to be considered when each new wireless system is installed, and should also be continuously monitored. A well-designed wireless system will have performance margins built in and will include extensive diagnostics to detect loss of margin due to radio interference and other considerations. ISA100 Wireless radio diagnostics include metrics that are specifically intended to detect and blacklist problematic radio channels automatically.

Based on real-world experience with all of these factors, users of industrial wireless are learning that wireless can deliver more than adequate performance for a wide range of applications.

Click here to read Jay Werb’s complete article on industrial wireless at InTech magazine.

About the Author
Jay Werb is the technical director of the ISA100 Wireless Compliance Institute (WCI), where he manages the organization’s compliance and other technical programs. He is also the editor and author of the data link layer (mesh) section of the ISA100.11a standard. Werb has more than 30 years of experience in the computer field, with the past 20 years focused on wireless. He has been the technical founder of multiple technology companies and holds more than a dozen patents. In addition to his work with WCI, Werb is a consultant with AIW LLC, where he assists end users with strategic adoption of industrial wireless instrumentation. He has a B.S. in biology and a master’s degree in management, both from the Massachusetts Institute of Technology.

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