Questions about reliability and squabbles over standards have made many automation professionals wary of using wireless technology for control and instrumentation—but not Mark Hass. For him, wireless instrumentation and control has been a key part of his plan for improving process reliability in the Crescenta Valley Water District just outside Los Angeles. In fact, going completely wireless was among the top projects on his agenda when he took the job as manager of technical services and information technology about six years ago.
Once he got the green light to proceed almost two years ago, Hass decided to work with Phoenix Contact (www.phoenixcontact.com), an automation vendor with North American headquarters in Harrisburg, Pa. With help from the vendor’s technical experts, Hass and his team expanded the district’s use of wireless communications by building a network of more than 24 broadcasting sites. The radios transmit data to the control room so the operators there can manage the 30 or so reservoirs, wells, boosting stations, and other assets in the five-mile-square district in the foothills outside Los Angeles. With this information, the operators can remotely control flows to about 8,500 water connections and from about 6,000 wastewater connections.
Because improving control over the system was a major motivation for going wireless, Hass gave a lot of thought to emergencies such as floods, wind storms, wild fires and earthquakes. “Emergencies tend to affect your communications immediately,” he explains. “A public utility depends on those communications to manage a lot of assets with a very small number of people.” As good a job as phone companies do during such emergencies, their priorities are not always the same as the water company’s, so retaining control over communications is very important to the water district.
Although the district contains commercial zones and serves some public agencies, it is mostly residential with a population between 35,000 and 40,000 people. So, not only must the district be able to provide the fire department and other emergency services with water, but it also must prevent any overflows in the sanitary sewers. “If we flood, that’s a public health hazard,” says Hass. And because, as the saying goes, things flow downhill, such hazards would spread much more quickly in this district than it would in others.
To show how wireless communications helps the district to avoid such hazards, Hass points to a power outage caused by wind storms at the end of last year. Although other areas in greater Los Angeles went without power for more than a week, the Crescenta Valley district was lucky in that it was in an area that went without power for only three or four days. Even so, “we continued to operate our district and provide 100 percent service because we had all of our telemetry and control systems running normally after we got our generators online,” says Hass. His district was without power for only about two hours.
Planning pays profits
Another reason that the district was able to maintain service was the forethought and investment that went into the network. Because of an investment in stronger towers and anchors, the district lost only one antenna during the storm. Also, a combination of prior planning and redundancy at almost every point in the system permitted rerouting of the signal transmission.
The ability to continue performing during emergencies was not the only return on the investment in a hardened infrastructure with built-in redundancy. The technology also solves problems that occur in day-to-day operations that span an entire community. “No matter how good a network looks on paper, all it takes to cripple it is for some business down the street to change the way it’s doing business,” notes Hass. “There is nothing you can do about the interference except to change your routing plan. If you’re not prepared to do that, you could be down for days or weeks until you find the problem and get a solution online.”
Even when the problem is a hardware failure that cannot be resolved by rerouting or some other simple adjustment, communications failures no longer occupy the staff as much as they did in the past. Diagnostic screens from Phoenix Contact help the operators and the telemetry technician to identify a problem radio within a few minutes. The telemetry technician can install a spare, upload a configuration, and work on the radio on his bench. There is no waiting around for the phone company or a vendor to show up.
Because this ability to find faults and reroute signals quickly, even in emergencies, was so important to the project, Hass included remote diagnostics, redundancy, and hardening of the infrastructure in his initial economic justification to management. “It cost a couple of extra months to really assess the problem and make sure that we understood our needs,” he recalls. “And then, it probably cost us an extra 20-25 percent in initial capital for extra radios, extra miscellaneous gear, and labor.”
Since the Crescenta Valley Water District completed the main phase of the project last fall, the extra investment has already shown what Hass calls both strategic and financial returns. “We have more control, and we’re able to operate with fewer people,” he explains. “In the old days, we had about three times more employees to run around and check reservoir levels, pumping stations and sewers.”
Even more savings accrue from not having to rely on other companies to maintain communications throughout the district. Because phone lines no longer transmit data, for example, wireless saves $25,000 a year in phone bills alone. Add to that wasted labor and other downtime costs associated with waiting around for the phone company to show up. “Based on the savings on the phone bills, we would have paid for this project in roughly six years, even with the extra expenses for redundancy,” Hass reports. “Once we factor in our labor and other miscellaneous and intangible costs, we’re looking at more like three years.”
Bringing the maintenance of the wireless assets in-house not only contributed to the financial returns, but also figured prominently in the strategic returns. “Besides saving you money in the long run, not having to go to an outside vendor for support for every little thing gives you that control, that quick response, that ability to make changes without going through a long process,” says Hass.
In fact, Phoenix Contact’s willingness to work with Hass and his telemetry technician was the reason that Hass selected Phoenix Contact as his wireless supplier.
“I needed a company that would work with us and be available during that training curve so that we could own it,” Hass says. “As I got further into the selection process, I got a sense that, if we had problems in the field that we had not seen before, we would have the ability to dialogue with the guy who designed that part of the hardware. It’s rare these days for a larger electronics company to give a smaller customer like us access to their technical staff.” Usually they insulate their design staff with their networks of distributors and systems integrators so they can concentrate on rolling out new products.
Wireless for control?
Although most wireless applications are for monitoring processes that span large distances, such as those at a water plant, the technology is also finding its way into control applications where the distances involved might be less than 10 feet but involve the harsh environment of the plant floor.
Take the machinery used by Miller Brewing Co. to fill 2,000 beer cans per minute. The programmable logic controllers (PLCs) running the machines need to track temperature, pressure and levels in the large, rotating bowl-shaped tank that holds and feeds the beer. Before the machines were fitted with wireless sensors from Phoenix Contact, wires came down from the roof and into the rotating bowls through a slip ring. Unfortunately, the slip rings were a maintenance nightmare because they would frequently snag and break the wires running through them. The costs were high.
“You’re talking both downtime in production and the maintenance costs,” notes Paul Mercier, business development manager for Phoenix Contact’s Industrial Electronics Group. When, however, one of Miller’s engineers found that he could end the nightmare by installing wireless sensors and stainless-steel battery packs, the brewer went wireless on its bowl-filling operations everywhere.
Because wiring and installation can easily account for half, and as much as 80 percent, of the cost of installing instrumentation in process plants and tank farms, more users are finding wireless sensors and battery packs to be attractive. Batteries, however, introduce their own set of problems—management problems that go beyond just replacing the batteries and disposing of them properly.
“For battery-powered devices, you may have to optimize the performance of the device either to gain maximum battery life or perhaps to maintain high-speed data exchange rates,” notes Gareth Johnston, global wireless product manager for ABB Ltd. in St. Neots, in the U.K.
Energy harvesting devices
To help users to minimize these problems or even to avoid them altogether, some vendors have been developing devices that permit instruments to harvest energy from the surroundings. Some harvesting devices might capture energy available from the sun or another source in the surrounding environment and convert it to usable electricity. Others might produce electricity from the vibration or thermal gradients generated by the process.
One example is a device being developed by ABB (www.abb.com) to use thermal gradients to power temperature sensors. The temperature transmitter and sensor are packaged with WirelessHart communications technology to eliminate the need for any cabling to the instrument. “Because quick and easy to install is a key feature of wireless, this particular instrument also has a built-in energy harvester, rather than a separate plug-in unit,” says Johnston.
Although the device is still about a year away from being released to the marketplace, ABB is currently conducting a series of field tests and one of these is at Robinson Brothers Ltd., a manufacturer of specialty organic chemicals based in West Midlands, UK. The prototype is monitoring temperature on a steam main supplying the plant. The transmitter sends data wirelessly to a remote gateway, which feeds the signal into the site’s existing Ethernet network and then to an ABB SM500F data recorder.
An onboard micro-thermoelectric generator (micro-TEG) generates the transmitter’s operating power using the temperature difference between the steam pipe and the ambient surroundings. The device being tested at Robinson Brothers needs the temperature difference to be at least 86 degrees F, which is no problem because the steam flows at around 229 degrees F (106 degrees C) and the ambient air is typically 79 degrees F (26 degrees C).
Although the transmitter contains a built-in backup battery, it does not usually rely on it during normal plant operation. “The transmitter has been operating for about three months now, and it’s ticking all the boxes without drawing any power from its backup battery,” reports Tom Rutter, electrical and instrumentation manager at Robinson Brothers. “It looks like it could go on forever, provided there’s steam flowing through the line.”
For this reason, Rutter thinks he and his colleagues will be using more of the energy harvesting technology in the future. Even though the 100-year-old plant already has more than 10,000 wired measurement points, it is still expensive to link new instrumentation to the host system. “There are terrific cabling costs involved in installing conventional instrumentation, so the potential savings are obvious,” he says.
Another energy-harvesting technology is EnOcean, which was recently ratified as an international standard under by the International Electrotechnical Commission (IEC). ISO/IEC 14543-3-10 is a wireless short packet (WSP) protocol optimized for energy harvesting. The standard defines the physical layer, data link layer and network layer of a protocol developed for ultra low energy consumption suitable for use with energy harvesting. EnOcean started out as a home and building automation standard, and it can already be found in 850 products in use in more than 200,000 buildings worldwide.
The EnOcean Alliance (www.enocean.com) is a consortium of companies working to develop and promote self-powered wireless monitoring and control systems by formalizing the EnOcean standard. The organization’s goal is to establish energy harvesting wireless technology as the wireless standard for sustainable buildings, and help bring about a broad range of interoperable wireless monitoring and control products for use in and around residential, commercial and industrial buildings. Automation vendors involved in the EnOcean Alliance include Beckhoff, Omron, Phoenix Contact, Siemens, Wago and others.
Advancements like these have made wireless instrumentation into a much more desirable technology. Because of this, Johnston at ABB has found himself fielding questions from more users about using wireless communications for PID (proportional, integral, derivative) control.
“Their concerns are that wireless would be too slow, and that is certainly the case with some applications,” Johnson says. Yet, in other applications, modifying the PID algorithm to account for delays in the wireless network seems to be the answer. “Early trials seem to suggest that these modifications are not too significant,” he says.
>> Click here to read another example of using wireless sensors for control at Hitachi Zosen Inova, a waste-to-energy plant in Switzerland.