Industrial Wireless Sensors: A User’s Perspective

There are many reasons to anticipate that the use of wireless instrumentation in industrial settings will increase dramatically in the next few years. However, certain stumbling blocks could curtail this deployment. As usual, cost and availability are critical factors when considering potential deployments. Installed and operating costs of the wireless instruments must be competitive with their wired equivalents if these instruments are to have widespread deployment.

Similarly, wireless offerings must be readily available in a timely manner, preferably from multiple manufacturers, to be able to get deployment traction. In addition, deployment of such instrumentation in an industrial setting—where security and robustness criteria are much more stringent than in residential settings—hinges on user acceptance of verified performance and security requirements as well as those mentioned above. As is the case for many technologies that they utilize, industrial users are typically not wireless system experts but rather technical staff members who have a measurement application for which wireless technology appears to be a viable option.

In 2013, as in recent years, these industrial users need to evaluate many factors when considering a wireless sensor network, including radio performance, battery life, interoperability concerns, standards compliance, and security. With many industrial users considering widespread deployment of wireless instruments, it is imperative that accurate information for applying the technology to real-world applications be available to the end user.

Wireless Sensor Applications

Sensing applications for which wireless sensor technology is a good solution are numerous in all types of process and manufacturing plants. Plant designers and plant operators are continually searching for new technology to improve their plant operation, performance, and reliability. But before making a significant investment in a new technology such as wireless sensor networks, a plant needs assurance that the technology is ready for industrial use and that the technology provides a clear advantage over an existing technology or provides a function not available with current technology. Which applications fit these criteria depends on many factors, including whether the installation will be at a new plant or an existing facility. Several potential applications are discussed below primarily from the retrofit perspective.

One of the most common wireless sensor applications today is enhanced equipment condition monitoring of critical plant machinery such as pumps, fans, and motors (Figure 1). Plant maintenance practices have become much more analytical in recent years, but the analysis depends on process- and maintenance-type data being readily available. In many situations that type of data is not easily available or not available at all. When most existing plants were built, it was not economically justifiable to install sensors on much of the less-critical machinery. Retrofitting wired sensors to collect the data is still too expensive, and periodically collecting the data manually is not an option due to staff reductions in recent years. Wireless sensors may greatly reduce the installation cost, enabling more data collection and resulting in improved proactive maintenance practices.

1. Remote data collection. The blue device in the center of the photo is a wireless sensor used to collect vibration data on a pump that was not previously monitored. Courtesy: Southern Company Services Inc.

Another example of industrial use of wireless sensors, and specifically wireless sensor networks, is in the power plant performance testing area (Figure 2). Performance tests are run periodically to determine the plant efficiency using special test instruments and data collection systems that may only be deployed for several days. Considerable labor costs and time are associated with running cables to all the test instruments. The use of wireless sensors could significantly reduce the time and effort required to set up and tear down test instruments for each test.

2. Wireless layout. This diagram documents conducting wireless sensor testing in preparation for utilizing wireless sensors for performance testing. Source: Southern Company Services Inc.

Probably the most common use for wireless sensors today is to monitor remote equipment where long wiring runs would be cost-prohibitive. These types of installations tend to be point-to-point applications using proprietary protocols and do not use the wireless sensor networks such as ISA-100.11a or WirelessHART.

Currently, the use of wireless sensors in industrial applications appears largely limited to monitoring functions rather than closed-loop control tasks. The use of wireless sensors for closed-loop control application will probably be very limited for several years until there is considerable experience using the technology on monitoring-only applications.

Barriers to Acceptance of Wireless Sensors

Whenever a new technology is introduced there are always barriers to its acceptance, and wireless sensors are no exception. The barriers include new technology, increased cost, standards confusion, concerns about the robustness of the products, and cybersecurity.

New Technology. There is always some inherent resistance to change due to uncertainty about the performance of a new technology. Industrial users can be very leery of deploying serial number 1 of anything, especially something as complex as a wireless sensor network. Once a technology has success in a similar environment, its adoption in the industrial world can increase dramatically and rapidly.

Increased Cost. Some of the early projections for wireless sensor costs were quite low, and this has led many industrial users to expect wireless sensors to have lower installed (lifecycle) costs than traditional wired sensors. However, based on the authors’ experience, so far that does not appear to be the trend with industrial sensors. The wireless portion of the sensor is merely added on to an existing wired sensor, which results in higher costs. The increased component cost can easily exceed the cost savings associated with wiring, particularly for those transmitters that are expected to be deployed for many years (it is not atypical in a power plant for a transmitter to be in one location for 50 years). There appear to be opportunities for low-cost sensors on many applications, but that may require a mindset change at many plants.

Standards Confusion. The fact that multiple incompatible wireless sensor standards currently have products in the market causes concerns for users that they may choose a standard that eventually will become extinct. There is also considerable uncertainty about what compliance with a standard means. For example, does compliance (or certification) with a standard ensure interoperability between vendors devices, and does it provide some certainty about security?

Uncertainties Concerning Robustness. Industrial products are expected to be near 100% reliable by most users and, for many users, there is not enough operating experience or published test results with the new wireless sensor networks to know whether they meet that expectation. Arguments that wireless networks can be made more reliable than their wired counterparts are difficult to make given that many consider (often incorrectly) the wired networks nearly 100% reliable, if not 100% reliable.

Cybersecurity. In power plants today, all wireless network products are subject to extreme scrutiny for cybersecurity vulnerabilities due to the NERC CIP standards. Because the wireless sensor networks are less familiar to IT personnel, they receive even more attention. In some companies, the wireless sensor network will only be allowed to communicate with the plant digital control system using nonroutable protocols, such as serial MODBUS. NERC standard CIP-005-2 Cyber Security Electronic Security Perimeter requires that each facility establish an electronic security perimeter for all critical cyber assets, but it is not clear how to do this for a wireless sensor network that is connected to the plant distributed control system. This hurdle will probably be an issue for several years to come.

Despite all these barriers, there are always a few companies that are willing to experiment with new technologies that show significant promise. These companies in some ways serve the industry as beta testers, and if the equipment performs as expected, other companies will eventually begin to use the new technology.

Multiple Standards Compete

Industrial standards play a very important role in today’s highly technical society. Many years ago standards were usually developed after several competing technologies were already established in the marketplace. Today in many cases, standards are developed before products reach the marketplace and actually drive the development of many commercial markets. Such is the case with wireless sensor networks. Three main “standards” have been developed, with each attempting to drive the development of wireless sensors in a particular direction.

The majority of wireless industrial sensor approaches now being deployed or being considered for deployment are based on these three different “standards”: the HART Communications Foundation’s WirelessHART (IEC 62591), the International Society of Automation’s ISA100.11a, and the Industrial Wireless Alliance of China’s WIA-PA (IEC 62601). Aside from these industrial automation standards, users must also be aware of the underlying wireless network standards IEEE 802.11, IEEE 802.15.4, and IEEE 802.15.3a and their interactions with the three principal industrial automation protocols mentioned previously. The main questions being asked by end users revolve around interoperability, reliability, and security.

If there were a worldwide wireless sensor “czar,” then there would probably only be one industrial wireless sensor standard, but in a real, market-driven environment, that will not be the case. Although the presence of multiple standards may be a barrier to industrial acceptance, it is the reality that users must accept, at least for the near future. A single standard for wireless may not be critical, as the airwaves (unlike wires) are pretty forgiving of multiple protocols. Smart phones today support four or five different wireless protocols, but the user sees a common interface in spite of the underlying protocol variability.

A number of standards issues remain that cause concern for users.

Is one standard “better” than another? With complex systems like wireless sensor networks and varying end-user requirements, there probably is no right answer to this question. The more pertinent question is, Does one or more of the standards meet the industrial user’s current and future needs? Even this question can be a challenge to answer without actually investing in a system and testing it thoroughly.

It is even more difficult being a seer and knowing that a technology will succeed in the marketplace and be available decades down the road. Although there is a wealth of technical information published on wireless sensor networks, most of it is not written to the industrial user audience and does not address the most fundamental end-user questions, namely cybersecurity and interoperability. Also, little of the published material is written by an unaffiliated author. Though skepticism is not always warranted, the end user often sees such material as advancing a vendor agenda and being biased.

Are standards useful? From an industrial user perspective, the most useful aspect of a standard is the strong expectation that compliance with a communications standard will ensure seamless interoperability between different vendors’ products (Figures 3, 4, and 5). The current wireless standards are quite complex, and there may be too little user experience to assess interoperability.

3. Swapping out wired transmitters. The typical end user has high confidence that this approach will work all the time. Source: Taft Engineering

4. Swapping out wireless transmitters. The typical end user has less confidence that this transition will work. Source: Taft Engineering

5. Multi-vendor wireless sensor network. This arrangement must ensure that full functionality is possible for all the sensors. Source: Taft Engineering

Based on limited testing by the authors, it appears that a third-party gateway will read the wireless sensor process variable reliably, but other secondary information may not be fully available. For example, if one vendor’s sensor is intended to measure vibration, can another vendor’s gateway bring back the spectrum information, or is the information limited to only the 1x or other aggregate values? Also, does compliance with one of these standards provide any guidance to the end user on the security of these devices?

Does it matter whether the standard is a consensus, industrial consortia, or de facto standard? Many people consider consensus standards—those produced by ANSI accredited standard-writing organizations—to be the only true standards. However, many commonly used and very successful standards have been developed by industrial consortia. Each method has its own strengths and weaknesses, but for most users, the standard development process is less important than the final outcome and manufactures’ adherence to the standard.

Is certified compliance necessary? Many questions are related to standards compliance, particularly with complex standards such as WirelessHART and ISA100.11a. Ideally, a trusted certification organization would thoroughly test all devices submitted, and those that pass would receive a certification that the device complies with the standard. This certification would be available to the user to provide assurance that the device is in compliance and meets some minimum functionality defined by the standard. This minimum standard should be clearly defined by the standards organization.

In reality, it is more complicated than that because the standards have a plethora of implementation options, which are very difficult to completely test. As a result, only a very limited set of options, often called a profile, is tested. If a user’s application requires a different set of options, then the certification may not be very useful. Similarly, it would be beneficial for any device labeled as compliant to be tested by the compliance organization to ensure it is, and to be “registered” as having complied.

Is there an independent and published assessment of the cybersecurity of wireless devices? This is perhaps the most important question that should be asked today. Ask not only if a device adheres to a standard but also if good coding practices and other design features are available that will make the device more intrusion-resistant. Also, does the compliance organization have a role to play in these security assessments, or is this best handled by an independent, third party? If the compliance organization is the exclusive assessor, there could be the appearance of bias. Whether handled by the standard compliance organization or an independent, third party, the methodology used to test cybersecurity should be made available to the end user.

Standards can certainly have an impact, either beneficial or deleterious, on future widespread deployment. If standards are clear to the end user and have verifiable compliance by certification or other means, they will reduce uncertainty and allow the end user to make informed decisions, thus reducing the technological risk. Having multiple, competing standards for wireless transmitters is in itself not a problem, as long as the marketplace is still robust and not so fractured that, in effect, a standard becomes one manufacturer’s proprietary workspace, locking end users into that single manufacturer.

Suggestions for Users

Given the current state of the wireless sensor technology, standards, and the market, what is an industrial user to do? First, as with most other new technology issues, users should clearly define their needs for sensors and consider whether wireless sensors are really the best option. This may seem so 1990s, but twisted-pair, copper wires and 4-20 mA signals could still be the best communication network and protocol for some applications. Users should gather as much technical information as they can consume from a variety of sources, including vendors, other users, technical interest groups, and the web. The idea is not to become an expert but rather to understand some of the terminology and be aware of some key technical issues.

Along these lines, it would be useful if an independent organization could produce an independent and vendor-agnostic user’s guide to wireless sensors.

Don’t wait for a single standard to emerge victorious, because that is unlikely to happen.

Finally, we suggest that users, after a reasonable investigation, purchase a small wireless sensor system and apply it to a noncritical application in their plant. There is nothing like actually using a system to increase one’s level of understanding and expose the system’s strengths and weaknesses.

Wireless sensors networks have the potential to significantly alter the industrial sensing landscape in the next decade, but before that happens, users must be comfortable applying the technology in their plants. Three major “standards” are currently vying for users’ affection, and it is very unlikely that a single standard will emerge in the next several years, so waiting is not a good choice. There are certainly barriers to the adoption of wireless sensor or any new technology, but with good preparation and cooperation from manufacturers, these barriers can be overcome.

Users should do their due diligence before making a major commitment to the technology. Part of the due diligence should include installation and testing of a small wireless sensor network system before committing to a complete system.

—Contributed by Wayne Manges (, Oak Ridge National Laboratory; John N. Sorge (, Research and Technology Management, Southern Company Services Inc.; and Cyrus W. Taft ( principal of Taft Engineering. This article is based on a paper presented at the 55th Annual ISA POWID Symposium.