Crossing AMR’s Iron Curtain
When it comes to radio frequency (RF) signal propagation, power utilities have it easy. Their meters sit on the side of the house, out of sight and for the most part, out of signal-soaking water. That is not always the case with water utility meters, many of which reside underground, in outdoor meter pits that are covered with cast-iron lids.
Not surprisingly, some utilities have trouble with RF signal transmission. In the brief case studies that follow, five utilities share the lessons they have learned in crossing a meter pit’s iron curtain.
Plano picks plastic
The city of Plano, Texas, has more than 73,000 automatic meter reading (AMR) units installed, and currently, 66,000 of them reside under non-metallic meter-pit lids.
“Early on, we realized that metal was going to be an issue with getting the signal out,” said Johnny Kemp, Plano’s field technology supervisor. RF signals reached only about 100 ft from under Plano’s older, cast-iron pit lids.
With its Datamatic AMR system transmitting signals at 3-second intervals, Kemp reported that his crew had to drive as slow as 10 mph to pick up reads.
Plano’s solution? Composite lids that are made of either plastic or polymer/concrete. Kemp and his crew tested several options before settling on this fix.
“When we first started out, we were thinking about changing out all our meter boxes to plastic boxes with lids, but that was just way too time consuming and expensive,” Kemp said. He also tried using a smaller plastic valve box beside the actual meter pit, which required running wires from one box to the next. “That was a big ordeal,” he said.
Plastic lids solved Kemp’s RF signal propagation problems, but he advises other utilities to consider some of the issues plastic presents.
Lid strength. In Plano, plastic lids work fine with smaller meter boxes, but Kemp said the city will likely use polymer/concrete lids or stay with metal for some of the larger, on-street meter pits.
“They’re a little more expensive, but there are load-factor issues,” Kemp said, adding that he plans to keep the metal lids on some larger pits in heavy traffic.
Multiple sizes. Because utilities add service hook-ups over time to keep up with new housing developments, one lid size will probably not fit all meter boxes.
“There are so many different sizes of meter box rims, you may need different sizes of lids to fit properly,” Kemp said.
The float factor. Occasionally, plastic lids do drift away from their meter-pit moorings.
“We’ve had some float away in heavy rains if the lid wasn’t locked down,” Kemp explained. He added that it was not a “huge issue.” It only happened a few times on streets prone to flooding.
Plastic meter boxes. Kemp also offered a piece of advice to help other utilities boost AMR efficiency with smart planning. “If you’re adding service hook-ups in a new area, consider installing plastic meter boxes. If you buy the box and lid together, you’ll get a better fit and higher load factor.”
Plastic pit lids provided a solution for the town of Leesburg, Va., which found nearly 15% of its meters underperforming.
“When you’re in an area with a lot of million-dollar homes, people don’t want to see a radio tower in the neighborhood,” said Herb Gallahan, assistant superintendent of the utility alliance division for the town.
To make matters worse, Leesburg is in a hilly area, but utility managers don’t have a lot of high-altitude locations to place data collectors for the utility’s Hexagram fixed-network AMR system.
“There aren’t any telephone poles in these areas because everything is underground,” Gallahan explained. “We didn’t have a chance to put up as many data collectors as we wanted.”
The result was that about 2,000 of the town’s 14,000 AMR units failed to deliver daily reads as specified in the contract.
“Hexagram has bent over backwards to work with us,” Gallahan said, adding that the company is footing the bill for plastic lids on the meter boxes with signal troubles. “The system is working fine everywhere we’ve changed out the cast-iron lids for plastic,” he said.
Raising the bar in Loudoun County
Kirk Marsh, manager of field services for the Loudoun County Sanitation Authority (LCSA) in Virginia, is in his second generation of Badger Meter AMR units. He hasn’t seen a lot of signal propagation problems.
“In most cases, we found that if the signal doesn’t get out, the unit has lost its program or the batteries are dying,” Marsh said. As early adopters of AMR, however, Marsh and his team have learned a thing or two about deploying the technology efficiently and cost-effectively.
Like many utility professionals, mangers at LCSA wanted AMR out of the sight and reach of customers. The team didn’t want to spark customer curiosity, Marsh said, and they also didn’t want transmitters attached directly to meter-pit lids.
“If a customer opens the lid, then shuts it without getting the wires tucked in, they’ll cut that wire,” Marsh explained.
That is why Loudoun County AMR units are attached to aluminum bars that fit into the meter pits a few inches below lid level. The bars, which are cut just an inch longer than the inside diameter of the meter boxes, install quickly with an upward tug, wedging them in tightly about 4 in. below the top of the box.
“A lot of people think the closer to the lid, the better reception you get,” Marsh said. “We’ve tested several ways, and we’ve found that if you bring the transmitter down a few inches, you’ll get better reception.”
To get signals out of the deep basements of commercial buildings, Marsh has the building contractor drill a hole in the wall during construction. These walls, made of concrete, can range in thickness from 16 to 22 in. LCSA personnel then place a screen over the hole and bring the transmitter up to the hole’s level.
Marsh also offered a final tip to AMR users: “Don’t put a transmitter right up against a wall. You want your transmitter sending signals into open space so that the signal can find air gaps and reach the receiver.”
Testing the technology
Although many utilities have immediate success with plastic meter-pit lids, others find they need to test products carefully to find the right manufacturer for their environment. That was the case in Harford County, Md., when Harford County Water and Sewer found that cast-iron lids dramatically reduced signal strength on some of its pit-mounted Itron encoder/receiver/transmitter (ERT) units.
“We were using a handheld receiver, not a vehicle-based unit, so we didn’t have as strong a retrieval method,” explained David Wilson, Harford’s supervisor of meter operations. Wilson noted that most of the trouble spots had signals reaching out 50 or 60 ft, but on some units, meter readers had to stand within a few feet of the meter pit to catch the signal.
Although the utility has approximately 15,000 AMR units in place, only about 4,000 of them are in meter pits. To get the signal past iron pit lids, Wilson tried products from several manufacturers. Sizing was an issue with polymer/concrete composite lids. Durability—or the lack of it—doomed some of the plastic lid options.
On one product, the area around the penta-bolt snapped off, and the worm gear broke away, leaving the lid sitting unsecured in the meter-box frame and not locked down, Wilson said. With another option, pit lids in or near driveways simply broke apart during summer months.
“We did a cold-weather test before deploying these lids,” Wilson said, explaining that a plastic lid is expected to be more vulnerable when it is cold, but that wasn’t what did the lids in—it was the summer heat.
“We’ve changed our testing based on that problem,” Wilson said. The utility stressed products with both freezing and heat guns that brought the pit lids to 120°F. After exposing lids to temperature extremes, Wilson had rock-loaded dump trucks driven over them, and then he picked the lids that survived. Those same pit covers broke when the trucks rolled over half a brick perched on top of them, but Wilson conceded that “it was the point load” that made the difference. “I feel very secure with our plastic lids now,” he said.
Another crush in Denver
Denver’s football team, the orange-jersey-clad Broncos, used to be famous for their “Orange Crush” defense. Denver Water dealt with a different kind of crush when the utility first started installing Itron ERTs on top of meter-pit lids for a drive-by AMR program.
“The first year, we just took the flat lid that we used on meter pits at the time, drilled a hole and connected the ERT to the meter through it,” said Cindy Hagood, customer service field supervisor for Denver Water. She added that the ERT “stuck up a little” on top of the meter box. “We soon found out that more people mow over their meter pits than we ever imagined,” she said.
Mower blades and aeration-equipment spikes were mangling the ERT electronics. To solve the problem, Denver Water bought new cast-iron meter-pit covers featuring an indentation for ERTs to sit recessed. This takes ERTs safely out of a lawn mower’s reach; however, the solution doesn’t protect devices from aeration spikes or gravel-filled driveways, where the point load of rocks can puncture the ERTs, Hagood said.
That is why Denver Water used some plastic lids as well as the special-order, cast-iron units. In addition to driveways, the utility also uses plastic lids in some high-traffic sidewalk areas.
“We don’t want the recessed lids in an area where a woman could catch a heel in it,” Hagood explained. “These plastic lids are flat, so there is no tripping hazard.” Denver Water also had some success mounting ERTs underneath the cast-iron lids and putting a plastic plug in the hole that had originally been drilled for ERT wiring.
Hagood is still looking for the right fix for some other situations. In Denver’s downtown, for instance, meter readers must do their drive-by at around 3 a.m. to reach meters in deep sub-basements of skyscrapers.
“Trying to pull a signal through 3-ft concrete walls is not that easy,” Hagood said. “At 3 a.m., there’s not much going on downtown, and we can pick up signals well; however, come 6 a.m., when buses and trains start running, signals face too much interference for quick meter reading,” she explained.
Downtown, Hagood and her team plan to try new signal repeaters that Itron has just released. The utility is also testing fixed network solutions from multiple vendors for hard-to-reach areas such as gated housing developments and security-conscious campus settings. One size does not fit all meter installations, Hagood noted, adding that there is always room for new approaches.
“We learn something new about this system just about every day,” Hagood said.