Communication is what's important. Whether it happens over a cable or through the air is irrelevant, so long as the link is secure and the data transfer is successful. Luckily, there are now plenty of avenues to make that happen, so wireless devices and methods are becoming as routine in process monitoring, data acquisition, automation and even control as sensors, I/O points, hardwiring, PLCs and DCSs--just like the toothbrushes, clean socks, car keys, sack lunches and other items that engineers, operators and other working people use daily.
However, wireless transmitters, antennas, site surveys and wireless protocols remain unfamiliar to many potential users. So it helps to know how those further along the learning curve use wireless to solve mundane, but persistent operational headaches.
Curing Common Complaints
For instance, Thames Power Services' 1,000-MW Barking Power Station near London recently installed 35 Rosemount 708 acoustic transmitters from Emerson Process Management to find more failed steam traps, leaking or misbehaving valves and costly boiler tube leaks, and reduce steam losses, feedwater costs and downtime (Figure 1). If a steam trap fails or a leak develops, an acoustic device in the transmitters reports sound and temperature changes, which are configured to alert operators of a potential problem. Ian MacDonald, Barking's senior control systems engineer, reports the transmitters immediately helped by identifying a leak from a high-pressure, super-heater steam trap, which would have cost £1400 for every day of downtime.
"Improving process performance is all about understanding what's happening around the plant and being able to respond quickly to any problems," explains MacDonald. "Wireless technology enables us to introduce additional measurement points quickly and cost-effectively at any location so we can gather more information to identify potential faults."
Later, Barking installed 15 more acoustic transmitters to monitor other problematic areas, including vent valves that can stick during start-up and pressure relief valves that don't seat correctly. Previous manual monitoring was time-consuming and also failed to indicate when or why a release occurred, increasing the chances of a safety, regulatory or environmental incident. The new wireless devices enable precise monitoring and alert operators when valves have opened for as little as 1 second.
Next, data is fed into Barking's existing Emerson Ovation control system, where noise levels can be trended to identify gradual changes. Repairs can then be scheduled during normal off-times to maintain maximum plant availability and avoid forced downtime. Using its existing wireless networks, more devices can be added at much lower cost than if they had to be individually wired-in. This gives the plant more opportunities for monitoring where it was previously cost-prohibitive, such as identifying blockages in Venturi eductors, which typically use inlet/outlet pressure differences to create suction and rapidly mix injected substances.
"Having already installed Emerson's Smart Wireless THUM adaptors for access to stranded HART diagnostic data in field devices, we were familiar with Smart Wireless," adds MacDonald. "The mobility and flexibility of the battery-powered wireless devices also allow us to run trials and move devices to different areas without temporary cables. As a result, we can spot early problems and improve response to malfunctioning equipment, enabling better planning and use of maintenance resources."
Finding the Right Fit
Probably the most important virtues on the road to wireless are patience and flexibility in researching, designing and implementing the most useful solution.
For instance, engineers at Valero Energy Corp.'s refinery in Wilmington, Calif., were introduced to wireless several years ago when a third-party, point-to-point wireless system was installed to extend process monitoring. However, it was cumbersome and took too much time to deliver data, according to Rick Felix, Valero's associate process control systems coordinator. So the plant's engineers sought improved wireless tools; implemented Honeywell Process Solutions' OneWireless site-wide in 2009; and have been tailoring it to suit their applications and enhancing performance ever since.
"Refinery assets are typically spread over a large geographical area. Plants are often required to monitor multiple points in applications involving level, flow, pressure and gas detection., and, up to 90% of the installed cost of measurements in these applications can be for cable conduit and related construction," says Felix. "Wireless networks make it possible to easily obtain point measurements in the most remote and hard-to-access locations without interrupting normal operations. Wireless systems can work consistently and reliably in areas previously considered impractical, and lower cost per I/O with wireless may justify projects that wouldn't have been feasible with wired transmitters."
Back on the wired side, Wilmington originally employed a Honeywell TDC 2000 DCS, and subsequent upgrades added TDC 3000 equipment, while legacy US stations were migrated to Experion PKS with new HMIs, Icon stations and Experion servers. The refinery is presently moving to C300 controllers, which will be used for blender control. The plant was commissioned in 1969 and expanded with alkylation and fluid catalytic cracking (FCC) units in 1982. It produces 15% of southern California's asphalt supply. Meanwhile, Wilmington's OneWireless R200 installation includes Honeywell's Wireless Device Manager (WDM), Field Device Access Points (FDAPs) and XYR6000 wireless transmitters.
"Our wireless network provides more reliability and ease of use than earlier systems," adds Felix. "Also, OneWireless supports multiple protocols and is simple to manage and operate. Our wireless system provides a cost-effective, manageable solution for non-critical process monitoring applications, including pipeline movement, flare monitoring, LPG purge gas pressure, heat exchanger temperature and tank high-level alarms."
Because Valero and the Wilmington plant were early wireless adopters, they've learned many valuable lessons. For instance, the plant's initial wireless transmitters and multi-nodes were installed by Honeywell and then handed over to Valero for day-do-day maintenance and expansion. "However, our staff encountered some problems, such as signal strength issues due to antennas that weren't wrapped well enough to handle the weather, and some other cables that corroded," explains Felix. "There were also some challenges in programming the multi-nodes."
So in August of 2012, Wilmington conducted a new wireless site survey, and migrated its OneWireless R120 systems to OneWireless R200. The multi-nodes were replaced with FDAPs, while R200 and WDM provided improved system reliability and connectivity and an intuitive, web-based user interface. They allowed integration of the wireless network with the plant's control system using industry-standard protocols.
So far, Wilmington's active OneWireless network consists of 30 wireless transmitters, 11 FDAPs, two FDAPs wired to the DCS, and the WDM connected via serial Modbus to the Honeywell DCS.
"R200 was a lot faster to deploy, and it lets us troubleshoot our transmitters much quicker," adds Felix. "Work on the R200 system has proven to be much less labor-intensive than with the original R120 system."
Though they need power routed to them, FDAPs do message routing, so users can connect wireless devices to the control network and route data from the field.
They also allow creation of a secure, ISA100-compliant, wireless network of field instruments which communicate with each other and route messages from neighboring field devices to controllers. Likewise, WDM enables gateways and security managers to make sure communications between field instruments and the plant are secure. They support a web-based user interface, allowing process and field engineers with basic IT knowledge to quickly set up wireless systems, and they reduce time required to commission, monitor and troubleshoot the wireless device network.
"OneWireless helps us optimize our plant processes and reliability, improves safety and security, and ensures regulatory compliance," says Felix. "It's been much more than just avoiding the cost of wire because the key benefit of wireless lies in the ability to integrate valuable data into control systems and advanced applications, while also sharing that data with other networked applications. Many other projects are now becoming possible for us, such as short-range site-to-site, using inputs in control, etc."
Water Goes Wireless
One of the best indications that wireless is taking over basic process control is its widespread adoption in municipal applications, especially in water and wastewater processes.
For example, Oslo Municipality's public works department recently replaced costly operator panels with connectBlue's Bluetooth wireless maintenance and operations devices at several hundred pump stations which manage water and wastewater flows throughout Norway's largest city (Figure 2). The Bluetooth units give the utility's ABB ITTM AC 800C control system an Ethernet interface and web-server access to process data on customized web pages, local dynamic data logging and access to the city's wide area network (WAN).
In addition, Oslo's staff can use Bluetooth handhelds to service machinery, adjust and reprogram each pump station on site, and connect with overall control systems. Connecting AC 800C to the WAN also enables personnel at the pump stations to automatically store software changes on the WAN server, so they no longer have to return to the control room to download program adjustments before proceeding to another station.
Likewise, regional water management association Aggerverband recently automated operations at its 200 x 41-meter Genkel Dam and its 8-million cubic-meter drinking water reservoir in Gummersbach and Meinerzhagen, Germany, with help from water management contractor HST Hydro-Systemtechnik in Meschede, Germany. To monitor water withdrawal, water levels, temperature, evaporation, wind velocity, and constantly check physical dam shifts in relation to its substrate, Genkel's new process control system needed to link 12 stations, including a "measuring raft" located in the middle of the reservoir and Aggerverband's central control room that monitors and controls several dams.
Consequently, 11 of the 12 stations implemented BC2000 bus terminal controllers with PLC functions from Beckhoff Automation, which were networked via a 1.5-km Lightbus ring and Beckhoff's ADS TwinCAT data transport protocol. However, reaching the raft required using Beckhoff's KN6551 wireless terminal, a radio link based on IEEE 802.15.2 and a solar power supply.
"These terminals, which can be integrated easily into the bus terminal system, use the 2.5 Ghz band," says Frank Huetger, HST's IT systems product manager. "A directional antenna ensures a stable radio link."
Revising When Needed
Because wireless is still a relatively new technology in many places, those reluctant to use it in the first place are quick to blame and dismiss it again when it has growing pains. So what wireless really needs most of all is a willingness to sometimes rethink, readjust and renovate wireless components, designs and layouts to achieve stable communications.
For instance, St1 Energy's petroleum refinery in the harbor area of Gothenburg, Sweden, uses Emerson's Rosemount tank gauging equipment and a mix of wired and wireless components for level and temperature measurements, but found it had no direct access from its control room to its Smart Wireless Gateway, which is based on the WirelessHART (IEC 62591) standard and collects data from the wireless field network. Ironically, to monitor their wireless network's status and configure devices, St1's technicians previously had to go into the field and investigate.
So St1 implemented a wireless link from its control room to the gateway via Emerson's Wi-Fi-based Pervasive Field Network (PFN) solution. PFN at St1 includes three of ProSoft Technology Inc.'s RadioLinx industrial hotspot units indoors connected to three remote, outdoor panel antennas. The first hotspot is connected to the gateway; the second serves as a repeater to achieve line-of-sight and relay data; and the third is in St1's control room, where it creates a Wi-Fi zone (Figure 3).
This layout enables operators to access the refinery's wireless field network from anywhere in the control room, via laptop PCs equipped with AMS Wireless Configurator, AMS Wireless Snap-On and/or TankMaster software. In fact, Snap-On software gives users a graphical overview of the tank farm, devices on the network and their status.
Likewise, Sunstate Cement Ltd. in Queensland, Australia, recently completed an $85-million expansion to increase capacity to 1.5 million tonnes, including installing a wireless local area network (WLAN) between three ship unloaders and four access points. However, the WLAN malfunctioned, and the unloaders couldn't communicate back to the main controller.
"At first, Sunstate Cement thought the problem was with Siemens' wireless equipment. They had very low signal strength, even from only a few meters away from the WLAN's access points, and there were communication dropouts between the main controller and the three RTU PLCs on the unloaders," says Falk Holman, Siemens Australia's networks product manager. "The first thing I found was that the initial installer hadn't conducted any WLAN channel planning, and there were so many collisions and interferences because the traffic wasn't coordinated between the four WLAN access points."
Holman explains that access collisions can be avoided by conducting space division multiple access (SDMA) or frequency division multiple access (FDMA) procedures. He adds that WLAN simulation software like Siemens' Sinema E can improve communication performance before installation.
"We also discovered that plant staff had installed 5-GHz antennas, but the network was configured for a 2.4-GHz frequency range," explains Holman. "Also, antennas on the access points were installed below structures and were too low and adjacent to solid concrete walls. So, after selecting the 5-GHz range for the network, we reallocated channels to each of the access points and the corresponding loaders." Holman adds that channels available for the network ranged between 149 and 165 (5,745 MHz and 5,825 MHz) for Sunstate's outdoor application. However, because there's a 2-MHz overlap between channels, Holman arranged the channels in an ad hoc order to prevent interference.
A second round of tests with a Cisco spectrum analyzer showed slightly weaker signal strength (-70 dBm or 48%), but much greater signal quality.
"Unfortunately, we still experienced communication dropouts," says Holman. "So, what else was wrong and why was it only 48%? Well, we found the installer used omni directional antennas, which can have high gain but a very small vertical lobe. So, when the loaders were parked, it was impossible for the antennas to have line-of-sight due to a big difference in the height of the mounting positions. Also, we noticed the antennas were mounted too close together. To use antenna diversity properly in a 5-GHz radio cell, we recommend using 20 times the wavelength as the clearance. And, locating two access-point antennas under a belt conveyor didn't help either."
Consequently, Sunstate raised its antennas from 2 meters to 5 meters and relocated redundant cable. "We found 5 meters of excess cable stuffed into a 1-meter channel, which can cause cable attenuation," adds Holman. "Luckily, we used this extra cable when the antennas were relocated away from the overhead structures and raised higher.
After making these corrections and using Siemens iPCF rapid roaming functionality, Sunstate's wireless system is operating as originally designed. In fact, Holman reports it's been running without interruption for more than 12 months without any replacement or added hardware.