Once you get free, it’s only natural to want to explore a little—and then a little more. Well, the same is true for wireless technologies in process control, which have evolved in recent years from cable-saving novelties to regularly specified solutions for bringing in signals that couldn’t be captured before. This move to the mainstream has also affected its users, and many are building on earlier wireless gains to extend their capabilities even further.
Such is the case with Hunt Refining Co., which adopted a pre-standard wireless solution for maintenance about six years ago in conjunction with a plant expansion, and came to appreciate and adopt wireless in its monitoring, reliability, optimization and safety applications. Hunt’s refinery in Tuscaloosa, Ala., is the largest supplier of paving and industrial asphalt in Alabama, much of which is used by nearby roofing shingle manufacturers.
The three-year, $1-billion expansion project was undertaken in 2010 to increase capacity at its 50-square-acre site from 52,000 barrels per day (bpd) to 72,000 bpd. As part of the expansion, Hunt built a hydrocracker, hydrogen plant, continuous catalyst regeneration (CCR) facility and dimethyl sulfate plant, and expanded its coker.
Alan Weldon, PE, technical services and safety director at Hunt, reports it began using wireless shortly after Emerson Automation Solutions introduced its initial systems in 2007 because the refinery needed to monitor tank temperatures in a remote location. “Our initial resistance was due to concerns about network reliability, security and integration into the existing DCS. However, acceptance grew as the wireless network was expanded to include sensing applications that address safety, environmental, reliability and process needs across the refinery,” says Weldon. “Potential savings also helped overcome resistance, and we installed three Rosemount 648 wireless temperature transmitters along with a 900-MHz 1420 Gateway and four additional 648s as repeaters. But we also had some bumps in the road.”
Wireless temperature monitors were added to more tanks at the Tuscaloosa facility the next year, but some power modules had to be replaced after less than a year of service. Weldon adds his staff and colleagues from Emerson determined that the existing, 900-MHz wireless network was experiencing choke points with too much data trying to pass through one wireless device on its path back to the gateway. Later, their journey into wireless continued when battery life issues delayed installation of more wireless temperature monitoring.
More reliability = more acceptance
Most end users, integrators and suppliers report that more reliable, higher-speed, easily installed wireless devices are driving its acceptance and expansion in the process industries. For example, where WiFi (IEEE 802.11a-n) or wireless Ethernet used to run at about 600 Mbps at 5 GHz in 2009, it sped up to 1 Gbps or higher at 5 GHz in 2013-14, and is up to almost 7 Gbps at 160 MHz at present.
Higher speeds have been accompanied by ongoing improvements of the primary wireless standards, including WiFi, ZigBee (IEEE 802.15.4), Bluetooth (802.15.1), Internet protocol version 6 (IPv6) over low-power wireless personal area networks (6LoWPAN) and other variants based on their radio, cellular, microwave or satellite roots. Several of these have been aided by the multiple-input, multiple-output (MIMO) method for multiplying the capacity of radio links by employing multiple transmit and receive antennas to use multi-path propagation, which improves data throughput and distance.
“We implement MIMO with four antennas, which allow multiple transfers of data in and out to enable very high reliability. We can send three streams and receive four, which make data packet losses much less likely,” says Divya Venkataraman, global product manager for wireless and network security at Rockwell Automation. “In addition, the wireless standards are continuing to evolve. IEEE, the WiFi Alliance and their partners are continuing to seek new ways to further eliminate data collisions and reduce network retries.”
Surveys and security essential
Despite these technical gains, pretty much everyone agrees that individual site surveys, audits and assessments, including radio frequency (RF) analysis, are still essential for deciding the best way to deploy wireless in each application.
“Audits can take into account distances, obstacles, noise, curvature of the earth and cellular coverage,” says Zechariah Hoffman, product marketing specialist for wireless at Phoenix Contact. “Some wireless technologies are more robust and may not need an audit, such as 900 MHz frequency-hopping spread spectrum (FHSS) because they can typically handle harsh environments. Wireless technologies operating in this frequency band usually have 1-Watt transmit power, which is the highest allowed by the U.S. Federal Communications Commission (FCC), making them ideal for many industrial applications. Using a licensed wireless frequency is another way to avoid doing an audit, but it also requires buying an operating frequency from the FCC.”
Hoffman adds that wireless is making similar gains on the security front. “Advanced encryption standard (AES) is a symmetric encryption algorithm on many devices, and there are various forms, such as 128-bit AES or WPA2-AES,” says Hoffman. “Frequency hopping on proprietary systems adds another form of security, which works because of the fast, constant changes to the frequency on which the radio is communicating. The pattern of frequency changes is different with each wireless network and manufacturer. Another security feature is Internet protocol (IP) or media access control (MAC) address filtering, allowing user access to only desired parts of the network.”