By Betsy Loeff, AMRA news writer
You might expect meters to be the star of the automatic meter reading (AMR) business, but they actually share top billing with the communication technologies that impact system capabilities. Four of the most commonly used communication options utilities use to connect with their meters are:
By far, the most widely represented AMR communications technology is radio frequency (RF) communications. According to the 8th edition of “The Scott Report” by Howard Scott, 82.6 percent of all AMR units deployed currently use RF communications. In 2003, approximately 9.6 million RF units were shipped to utilities. The next most popular communication technology, the power line carrier (PLC) options, saw just over 2.1 million units shipped.
In the AMR world, utilities can choose fixed RF networks or mobile RF technology. With fixed networks, endpoints talk to a neighborhood data collection unit, which often is a street light-, tower- or pole-mounted device that then connects back to the utility via a wide area network (WAN).
There are various topologies of fixed RF networks, including star, redundant star, mesh and tree networks. For mobile RF technology, commonly known as drive-by AMR, a vehicle-mounted data collection unit canvasses an area, gathering reads from the automated meters.
Factors to Consider
Transmission speed: How much data latency, or wait time, can you tolerate? That’s a question Michael Schleich, Itron’s director of AMR product marketing, encourages utility managers to consider. “The correct RF network topology-the shape or arrangement of the system-will be able to get the information from all of the meters to the home office in a matter of minutes,” Schleich said. He also noted that if you want to read all of the meters under a given substation, the time period to do that with a power line communication system could be hours. “With a redundant star RF network, it isn’t out of the questions to have all of the data at your neighborhood collector within seconds, and at the head-end within a couple of minutes,” he said.
The oldest, most proven form of fixed network for AMR is that which uses power line communication technology.
Platform permanence: Relying on public networks all the way down to the meter can be tricky business, notes Rob McEver, Cellnet account manager. Though McEver recognizes the infrastructure savings in using a network built by public carriers, he also advises utilities to consider the speed with which those public networks evolve. “Some networks have reached obsolescence in just a few years,” he said. “Other networks have required significant updates of endpoint devices to remain viable.”
How do you avoid the potential for costly AMR meter replacements? Use a private RF network for the local area network (LAN) that reaches endpoints, and use a public network for your backhaul of data from the neighborhood data collection/concentration unit.
“If the communication device that uses the public network becomes obsolete, only the device in the data concentrator needs to be changed at a fraction of the cost of changing all the meters,” McEver said. Schleich adds that with this approach, the re-occurring operational cost of the system is minimized because the neighborhood collectors aggregate hundreds to thousands of meters into a single public network connection point.
Migration: Do you want a mobile or fixed network system? “Some RF technologies such as mesh networks force you to commit to a topology, while others like star networks allow migration or even coexistence of different reading technologies,” Schleich said.
Flexibility: Combination utilities often are attracted to RF’s ability to serve gas, water and electric meters-and any combination of the three. But other technologies are catching up in flexibility. Utilities can easily find PLC systems capable of reading any meter. The same is true for cellular and IP options, and mesh network providers are looking to expand into all meter types as well. Schleich recommends combination utilities examine operational and maintenance advantages in having a common AMR technology for different service meters.
Meter density: Mobile RF generally is considered a cost-effective way to automate meter reading, but when it comes to fixed networks, that’s not always the case. Many utilities find that RF fixed networks are more suitable to urban and suburban service territories than rural ones.
Tower sites: In an RF system, the location of the neighborhood data collection unit determines signal reach. “Think of a cone coming down from the data collection point. The higher you mount it, the more the sides of your cone spread out. If you mount the cone too low, you might not have a large enough footprint for your antenna signal,” Schleich said.
Most collectors are installed on utility-owned power poles, with some systems using much higher transmitter sites. Municipal utilities can take advantage of antenna patterns and mount collectors atop schools or water towers. “As a rule of thumb for a star RF network, you can have data collectors that are mounted street-pole height spaced about a mile apart,” Schleich added.
RF holes: Because of physical obstructions such as buildings and terrain, no RF system provides coverage in a perfectly circular pattern. Communication systems can wind up with RF holes or nulls, which are localized spots in which networks lack coverage. The situation is easily remedied with signal repeaters. When used with a star network, the repeaters also can provide a low-cost solution to provide redundant coverage over the endpoints. That topology is called a redundant star network. Another fix? Mesh networks-where signals can move from meter to meter-or cellular technology.
Kevin McDonald, Georgia Power metering principal, manages an AMR system with nearly 100,000 endpoints in a utility that serves 2 million customers. Nearly 80,000 of those endpoints use drive-by AMR. “We automated those meters in the mid-1990s because they were in dangerous sites or hard to read,” McDonald said. “At the time we made that decision, it was the most economical approach.”
Having found a workable solution for meter sites where reader safety was an issue, Georgia Power is now piloting an RF fixed network at 15,000 sites. “Costs have dropped dramatically on fixed network technology, and we are looking at the possibility of widespread use,” McDonald said. “If we add a fixed network, we want more than just a monthly meter reading. We want daily data, power outage and restoration information, tamper alarms and the ability to check our meters regularly.”
If you think you’re unfamiliar with mesh networks, think again. The Internet is a type of mesh network. In it, traffic travels from point A to point B, but it is routed through intermediate points and rarely follows the same path each time.
Path flexibility is a feature of AMR mesh networks, which are a particular type of AMR solution that uses RF technology. More precisely, mesh networks are those in which nodes (or meter endpoints) can receive and pass along information not intended for them, according to John Brett, vice president of Tantalus Systems Corp., a mesh network AMR provider. That means any node in a mesh network can become a link in a daisy-chain network topography.
Contrast mesh networks to star networks, the typical fixed RF network topology: In star networks, a central control point functions as a server that communicates one-on-one with each node in the network. Or consider bus networks, which are representative of PLC systems. In bus networks, all the endpoints follow the same path home to the central server. If a node loses contact in either a star or bus network, it can’t communicate. And losing contact can happen easily. A tree leafing out, parked truck or other significant temporary obstruction can interfere with RF signals. Similar interference might occur in tree networks, which use a hierarchical protocol to determine communication paths. If the path fails, a node will be orphaned.
Nodes, or meters, are less likely to be orphaned in mesh networks. “Because nodes in the network can forward messages, the networks have built-in redundancy, which means they can hop messages around obstacles,” Brett said. “They’re self-healing, too. Mesh networks don’t require human intervention to re-route messages around failed endpoints.”
Factors to Consider
Ease of installation: A major advantage of mesh networks is that the AMR device in the meter acts as the LAN communication infrastructure. No dedicated collectors or other devices are required. Once the WAN connections are established to the meters that are earmarked as take-out points in the mesh network, the remainder of the system consists of the automated meters.
To keep installation simple, Brett counsels utilities to look for mesh networks that are self-configuring. “Some networks send data through multiple paths simultaneously. Some send data through only one path at a time, but never the same path. Others may use a single path, and it may use the same path for all transmissions until a problem crops up, and then it will search out a new path when necessary.” Sending redundant data up multiple paths can consume significant bandwidth. Consider looking for a system that sends data via one path at a time.
Nevertheless, Brett maintains it doesn’t really matter what communication protocol the network follows as long as the network is smart enough to know where the meter resides. “You still have to associate a meter serial number with a customer, but avoid networks that require you to associate meters with network parameters. Self-configuring networks make installation quicker. The configuration issue should be transparent to your installers.”
Battery life: Itron’s Schleich notes that mesh networks require extensive protocols to allow endpoints to manage multiple communication paths. “That communication protocol presents a large overhead on any standard message you’re sending,” he said. In other words, some of the data sent is data that manages path progression. “If you’re transmitting on battery-powered units, you’re transmitting extra data, and that can shorten battery life.” While electric AMR devices rarely use batteries as a primary power source, battery life is an issue in gas and water AMR applications.
Field-initiated messages: Brett invites utility managers to envision a kindergarten teacher of 12 students who tries to spend five minutes per hour with each child. “If the teacher goes from child to child, think about the little one who just finishes up his five minutes, then raises his hand to go to the bathroom. A teacher on a schedule would make the child wait 55 minutes until it’s his turn for attention again.”
Brett extends that analogy to AMR equipment and encourages utility managers to look for systems where endpoints have the power to field-initiate messages when nonstandard conditions arise. With a field-initiated message system, you can learn about outages immediately. The alternative is a system where meters must be polled before they can report their conditions.
Nominal range: Whatever range a vendor promises is the system’s nominal range. “Expect your actual range to miss or exceed the nominal mark,” Brett said. “It all depends on the circumstances. Range is a function of transmission power, receiver sensitivity and path loss due to factors such as foliage in the area or aluminum siding on buildings.” To better gauge range, find out how the product works in heavily obstructed environments vs. wide-open areas. And ask about the line-of-sight range. It will almost certainly be higher than the nominal range guaranteed by the vendor.
How many hops: Mesh networks extend transmission range by hopping messages from end-point to end-point. Most systems have a limit on the maximum number of hops a message can make before it must reach the WAN take-out point. “If you’re using technology with a short range and your mesh network can go only three hops, you won’t get very far with your transmissions,” Brett said.
Error-correction performance: What percentage of a single data packet can be lost in transmission without losing all the information you need? Brett notes that it isn’t unusual for AMR systems to lose up to 10 percent of data without losing all the necessary information. But smart systems with high error-correction performance can handle up to 40 percent data loss.
Backhaul: “Here’s what people aren’t thinking about,” Brett said. “Mesh networks cover only the local area network to the meter. They don’t bring the data all the way back to the operations side of your utility.” To get the data back to the utility, you’ll need to employ a WAN, and the topology of that network can have dramatic impact on system performance.
Brett notes that the star network topology is common for public network WANs. “A main server in the middle of the network can talk to only one mesh network at a time, and it has to poll each network separately.” That process delays outage notification to a utility mainframe. “You want a robust network configuration for beyond-the-read applications,” Brett said.
After two years of carefully reviewing AMR technology, Hugh Bridgen, manager of stations and metering at Chatham-Kent Hydro, an electric utility in Ontario, is now piloting a Tantalus mesh network. The move is a step toward fulfilling C-K Hydro’s advanced metering goals, but the trial comes at an opportune time to help the utility meet the Ontario Energy Board’s Smart Meter Initiative that will require all Ontario utilities to install advanced metering by 2010.
Why did C-K Hydro pick a mesh network? “Communications drive functionality,” Bridgen said. “There are many companies that have two-way communications, but to me, true two-way communication involves going back and forth all the time. For example, when a system uses a phone line and you have to interrogate the meter, you get only an idea of what’s happening in that instant. You don’t get a view of what is happening when the communication link isn’t in effect, so I believe in communication by exception. If there are outages, your system reports in. If there are voltage problems, you’re notified.”
Power Line Communication (PLC) Systems
The oldest, most proven form of fixed network for AMR is that which uses PLC technology. PLC technology uses a narrow-band signal to send transmissions over a utility’s own distribution wires. Because PLC systems ride an electric utility’s wires, they eliminate the need to build out network infrastructure. In addition, PLC systems go anywhere the utility sends current, allowing the system access to each meter to be automated.
Factors to Consider
Meter density: “Power line systems are rooted in rural applications,” said Todd Headlee, chief technology officer for Hunt Technologies Inc. “When you have to drive 10 miles between homes, the cost-per-read is high, so rural utilities traditionally have been able to more easily justify AMR deployments.”
Headlee added that a misunderstanding surrounds PLC systems. “Some people think the technology struggles in urban environment. It doesn’t. Today, there is more pressure on utilities to deploy fixed network technologies for purposes beyond billing. Compared with other fixed network options, PLC systems are very cost competitive.”
Functionality pluses: Because of their integration with the distribution system itself, PLC systems are ideal for distribution system maintenance applications such as signal strength analysis and phase identification. Signal strength analysis involves monitoring weak signals or meters that have lost communications that indicate line loss to determine where crews should check the system for tree limbs, hot clamps and other distribution network problems. Phase identification comes in handy when maintenance crews switch homes from one phase to another. “When the AMR system automatically records phases, you don’t need to track them manually,” Headlee said. “That facilitates phase balancing, which cuts wear and tear on distribution assets.
Flexibility: As the name of this technology implies, to have a PLC system, you have to have power lines. However, one of the two major PLC vendors currently offers a solution for reading water meters, and the vendor will add a solution for gas meters within the next year. The other major PLC company plans to launch gas and water solutions in 2005 as well. This makes PLC technology a fixed network option for combination utilities.
Data latency: Compared with other fixed network options, PLC systems may have varying degrees of data rapidly available. For example, widespread on-demand reads may occur over a period of time rather than instantly. Still, PLC systems do provide prompt outage notification. “When the meter is out of service, it quits sending data. You know which meters are out, and you can quickly send troops out to fix the problem,” Headlee said.
All the numbers, all the time: As steadfast monitors of all activity on a distribution system, PLC systems are relentless recorders of outage events, momentary outages (or blinks), outage duration and other quality indices many public utility commissions require utilities to record and report. But that’s a mixed blessing.
“There is a lot of room for judgment when you’re determining what should apply to power reliability indices,” said Greg Harrington, system engineer for Nolin Rural Electric Cooperative Corp., a Kentucky utility with more than half of its 30,000 meters hooked up to AMR units from Hunt Technologies. “IEEE standards have a more lenient view of what an outage is, and they allow you to pull things out of your power reliability index statistics. With our PLC system, everything is in there.”
Harrington notes that while he has asked Hunt to give utilities more flexibility with quality index limitations and definitions, he has mixed feelings on the subject. “If you’re allowed to pull numbers out, you can make your indices whatever you want them to be,” he said.
Nolin Rural Electric Cooperative Corp. picked a PLC AMR system as a cost-effective alternative to manual meter reading, said system engineer Greg Harrington. With only 16,000 of its 30,000 meters deployed, the utility already is finding value that wasn’t initially included in its business case.
Even without a stand-alone outage management program in place, Nolin is using the PLC system in restoration processes. “After a storm rolls through, we pull up the outage tracker built into our system and see where meters are not answering back,” Harrington said. “During a storm in September, we found nine instances of services down-mostly barns or pumps-where no one had called in the disruption. We also find hunting cabins without power. By being proactive with restoration, we don’t have people discovering the power is out when they drive up for the weekend, which would mean we’d have to send someone on overtime to make the repair.”
The utility also uses its PLC system to guide its tree-trimming schedule. “We’ve had a ton of rain in recent years, and our growth cycles have picked up. Where we’re normally on a four-year trim cycle, we’ve had to go back in three years. We look at areas with blinks and momentary outages, and those where we send the tree-trimmers,” Harrington said. “We’re able to trim smarter.”
You don’t need to be a rural utility to benefit from PLC technology. PPL Utilities, a Pennsylvania electric company serving nearly 1.3 million customers in suburban and small urban areas, uses two-way powerline technology from Distribution Control Systems Inc. (DSCI).
“We had one business requirement that couldn’t be compromised,” said Bernie Bujnowski, manager of PPL’s AMR program. “We wanted every customer to receive the same benefits from any system we put in.”
With that in mind, Bujnowski and the PPL team opted for a PLC system that touches every meter in the utility’s distribution network, from PPL’s urban network systems to the utility’s most remote customers.
“We also wanted a system that delivers more than monthly billing reads,” Bujnowski said. “We’re in a deregulated market, and we believe an AMR solution that provides more than monthly reads supports Pennsylvania public policy. Retail shopping among residential classes is non-existent in our territory now, but we believe it will happen some day in the future. Being able to support time-of-use rates and other rate structures puts us in a better position to offer customers more choices.”
“I’d love to be a bus or train commuter instead of having to drive my own car,” said Ron Chebra, managing consultant for PA Consulting. “It’s guaranteed cheaper than using your own car.”
That reasoning is why public cellular networks are the AMR technology of choice for many utilities, especially for the important commercial and industrial customer segment. “You know public carriers are going to be at the forefront of technology. They’ll continuously monitor and upgrade their networks,” Chebra said.
Of course, that can be a disadvantage, as many utilities discovered when the FCC ruled in August 2002 that that cellular companies no longer would be required to maintain aging analog networks. Although the agency planned a five-year phase-out, many analog networks are already history, which has left some utilities scrambling for alternatives and digital upgrades to their AMR systems.
Still, cellular technology offers a handy option, especially in areas where a utility has patchy AMR needs. The technology eliminates the need to invest in private network infrastructure, yet still offers impressive coverage. “Utilities get to coattail on the fact that there will be more and more towers, and cellular service is a growth industry rather than a static network environment,” Chebra said. “Cellular companies will go where the people are.”
Factors to Consider
Cost: Using a public wireless network, you’ll be paying a monthly phone bill for each AMR endpoint. However, rates are coming down. “When number portability became available for wireless service last November, it prompted 40 million people to switch carriers in one year,” Chebra said. “It really upped competition and drove rates down.”
Negotiating power: Utilities have more pull than they realize, Chebra noted, explaining that as traditional cell phone use reaches saturation levels in the United States, carriers are looking for secondary uses for their networks. “That’s why we’re seeing the proliferation of services like text messaging, camera phones and downloadable ring tones. The carriers have been adding vertical services to increase their margins on their basic network infrastructure.” AMR offers carriers a desirable, guaranteed usage, and often that usage is in off-peak hours. Chebra points to one utility that reads meters nightly between midnight and 3 a.m. “That meter read is almost a service to the wireless provider because it provides a nightly heartbeat reading to prove the network is up and running.”
Cyber security: “Meter reading may not represent a cyber threat to a utility, but putting data on a public network and opening doors to access increases the threat of cyber intrusion,” Chebra said. “For example, if I look at the energy consumption in a house, I can tell if no one is home.” Chebra also raises the possibility of hackers playing havoc on load control devices or resetting peak usage to lower demand rates for industrial customers.
Florida Power Corp. recently started upgrading its analog AMR for customers with peak consumption of 1 MW or more. The utility opted for a Comverge digital solution, choosing to stick with wireless service rather than a landline technology. Costs for the wireless technology are 20 percent of costs associated with maintaining a traditional landline system.
Georgia Power uses a cellular solution for C&I accounts as well. Although the utility has a combination of mobile and fixed network RF AMR for some 100,000 residential customers, approximately 2,500 customers at 250 kW or higher are read using a public carrier cellular solution. Why? Those C&I accounts are on real-time pricing, and Georgia Power pulls down data each morning to check reads. “If we see problems, we can respond immediately,” said Kevin McDonald, metering principal for the utility.
“Cellular is a good option for large industrial accounts,” McDonald adds. “It allows you to serve customers cost effectively with a sparse network where you lack meter density to use an alternative technology.”à¯£à¯£
Editor’s note: This article is excerpted and adapte from an article that originally appeared in AMRA News, a publication of the nonprofit association AMRA (www.amra-intl.org). Betsy Loeff is a news writer for AMRA.