If you think it’s hard to get a reliable Wi-Fi signal in your home, just imagine how tough it must be grab one atop an oil rig in the Gulf of Mexico, or on the noisy floor of an auto factory in Detroit. Those places are full of heat, vibration, and metallic surfaces that can weaken, reflect, and block signals. As a result, factories and industrial facilities have been slow to adopt new wireless equipment and devices that would otherwise save both time and money.
Many wireless engineers and factory owners know this, but it has been difficult for anyone to improve the situation. The impact of industrial settings on wireless performance hasn’t been studied in any systematic way, so it’s often impossible to predict how a new piece of equipment will perform on, say, a manufacturing line until you actually put it there.
To make it easier for factories to integrate new wireless technologies, U.S. federal government employees took it upon themselves to measure the performance of radiofrequency signals in three factory settings: an auto transmission assembly facility, a steam generation plant, and a small machine shop. They recently published their results as part of an ongoing $5.75 million project aimed at improving industrial wireless led by the National Institute of Standards and Technology (NIST).
For factory owners, there are many potential advantages to switching to wireless. They can avoid the costs and hassle of installing wires, and more easily reconfigure their facilities in the future. Wireless setups may also be safer, because employees won’t trip over bundles of cords. That’s why companies including GM, Ford, Chevron, Boeing, and Phoenix Contact (a company that specializes in industrial technologies) have all expressed interest in incorporating more wireless into these facilities.
“Right now I know that people are interested, but what they're worried about are the impacts to productivity or to the operation,” says Richard Candell, the project lead for the five-year NIST project, which is scheduled to conclude in late 2018. “They want to know that if they're going to use wireless, it's going to work just as well as the wired solution.”
Justin Shade, who focuses on wireless products for Phoenix Contact, says there’s no shortage of ways in which wireless could make factories and their workers more efficient. For example, manufacturers could use it to incorporate robotic arms into assembly lines. Today, robotic arms are often hooked up to control panels by flexible cables. Wind turbines rely on similar cables to maintain contact between the hub of the turbine and each individual blade. But these cables frequently break. In both cases, replacing them with wireless controls could save money and time.
Unfortunately, factories are also full of processes and materials that block or weaken wireless signals. For now, wireless technicians play it safe when installing new equipment by setting up redundancies, keeping wireless devices within close range with clear line of sight to their targets, and performing extensive testing prior to industrial installations.
Given the circumstances, Shade says it’s hard to fault factory owners and their technicians for being cautious. “If you're on the manufacturing line and a car door doesn't get made correctly, you're losing hundreds of thousands of dollars an hour, so the adoption has been a little slower in the industrial world,” he says.
Candell at NIST hopes their latest research can help industry operators predict how new systems will perform before they are installed. To take their measurements, the team visited an auto transmission assembly plant in Detroit, Mich., a steam generation plant at the NIST campus in Boulder, Colo., and a small machine shop that specializes in metalworking for NIST at their facilities in Gaithersburg, Md.
The group tested wireless signal propagation at two frequencies: 2.25 gigahertz and 5.4 GHz. These frequencies are reserved for the U.S. government, but fall close to the popular unlicensed 2.4-GHz and 5-GHz bands commonly used in wireless devices. Performance at these frequencies can therefore be considered comparable to what can be expected for wireless gadgets the rest of us use.
From their measurements, the researchers concluded that industrial settings have strong multipath characteristics, which means that signals tend to reflect many more times before they reach the receiver than they would under normal conditions. The practical impact of these reflections can be positive or negative, depending on the technology and how it is configured.
To dig deeper, the group used a metric to measure wireless performance called the K factor. It compares the combined power of all the reflected signals to the power of a line-of-sight signal with no reflections. A higher K factor means there is less fading due to reflections. In an open outdoor area, the K factor would typically be between 6 decibels and 30 dB. In the group's industrial measurements, they found lower average K factors of -5 dB to 6 dB.
Next, the NIST team used their measurements to estimate the average delay spread for the industrial facilities. Delay spread is the time it takes for all of a signal’s reflections to reach the receiver. They found an average delay spread below 500 nanoseconds. The group suggests this delay may not noticeably impact devices operating at 256 kilobits per second but could affect those that run at faster bit rates.
Another part of their analysis examined wireless performance in “metal canyons,” which are common in factories. A metal canyon is an area with metal surfaces (such as walls or large pieces of equipment) on at least two sides and a concrete floor below. In these areas, the group measured path loss, which describes the attenuation of wireless signals, and found that it is 80 dB, at a minimum, in metal canyons. For comparison, the path loss in an open area would be perhaps 40 dB after a signal at these frequencies traveled approximately one meter.
Candell says that, in practical terms, this means a wireless signal could reliably travel about 200 or 300 meters outdoors, whereas, in a metal canyon, a user would probably start to notice some issues with the signal at just 30 meters away.
With the results of their measurement campaigns, the NIST staff also built a software simulation of a chemical reactor and a wireless test bed that can replicate other industrial settings at their campus in Boulder, Colo. Candell wants to use these tools to generate hypothetical changes in performance and cost related to installing new wireless schemes in factories or other facilities.
“Ultimately, at the end of our five-year project [which is scheduled to conclude in late 2018], I want to actually produce industry guidelines to help people select and deploy these wireless devices effectively in their factories,” says Candell.