By Larry Helwig, Nevada Power
An automatic meter reading AMR system stripped down to its most basic elements consists of meter endpoints, concentrating and collection devices, network servers and, finally, the utility’s meter data management system. A robust and reliable communications system is essential to connect these building blocks. It is often this communications component, not the metering hardware, that proves to be the weak link in an AMR system. The choice of AMR communication technology is very important and should be matched with the utility’s ultimate business needs for its system.
A typical AMR communication system consists of three necessary components: the transmitter, the communications path and the receiver. Most AMR system offerings make use of either wireless radio frequency (RF) or wired power line carrier communication paths and transceivers located at meter endpoints and collection points.
Two communication system types associated with AMR are one-way and two-way. One-way systems are push capable while two-way systems are push, pull and poll capable.
There are also three types of communication modes commonly associated with AMR: mobile wireless, fixed wireless and fixed wired. Two-way fixed systems show the most capability in terms of supporting extended functionality such as outage management restoration and customer disconnect/reconnect capabilities. When making communication type choice it is essential that utilities consider the future intended functionality of their AMR systems. In an effort to save costs, some utilities choose too simplified a system and trade off this additional functionality.
Mobile wireless AMR communication systems have become popular because of their lower cost and the fact that they require less overall backhaul infrastructure. These systems read meters using walk-by and drive-by techniques via ERT radio read. Because these systems are not truly fixed their functionality beyond meter reading is somewhat limited. However, in terms of overall system cost, mobile communication systems can be very competitive.
Fixed wired AMR communication system options include narrowband power line carrier (PLC), telephone and Internet protocol. PLC systems have become quite popular in recent years. The advantage of PLC systems is that the wires are utility-owned, have long range capability and are virtually independent of geographical terrain. However, PLC systems are inexorably linked to the power distribution system and are directly affected by any modifications made to it by the utility. When considering PLC, the distribution system must be thoroughly analyzed from its metering endpoints to the chosen concentration points (usually at substations) to ensure that it is a communication medium capable of passing the AMR data signals. In these systems additional system costs can also be incurred in the form of line traps, coupling devices or power distribution apparatus that is PLC communications signal compliant.
One advantage of using Internet IP as a communication system is that the infrastructure already exists, and it provides very high data transmission rates. However, to ensure that such a system works universally, utilities would have to work with multiple Internet service providers to develop a system that has full compatibility with various hardware and software platforms utilized by their customers.
Fixed wireless AMR communication system options consist of public radio systems, (paging, GPRS), private radio systems, (licensed and unlicensed), and satellite systems.
When choosing a wireless AMR system, a utility should consider several factors. The target area’s population density dictates endpoint-to-concentrator ratios. Some wireless systems are more suited to higher population densities while others are better suited to suburban and medium population densities. It is always worthwhile to remember that for a given amount of radiated RF power the greater the frequency the shorter the transmission distance. The majority of wireless AMR offerings utilize unlicensed frequencies in the UHF (300MHz – 3GHz) radio frequency band.
Another issue utilities face when choosing wireless AMR systems is the placement and siting of data concentrators. Some mesh systems utilize concentrators as metering endpoints. Other systems ensure adequate coverage and mitigate propagation issues by installing collector concentrators at higher elevations, usually on local streetlights. If the utility does not own these structures they would need to negotiate joint use agreements with local entities.
Satellite AMR systems are not as popular; however, the basic idea appears to be well-suited for remote, isolated areas.
In fixed wireless AMR systems, network topology is another parameter where there are numerous options. Older systems tend to use hierarchical, star and point-to-point communication techniques. In recent years mesh and hybrid mesh networks have become more popular and have proven to be very reliable in densely populated areas. In a mesh network, each node or endpoint acts as a repeater capable of forwarding data. This creates multiple paths to collection or take-out points and eliminates some difficult non line of sight RF transmission issues. Most of these networks utilize the 900MHz and 2.4GHz unlicensed portions of the RF spectrum.
AMR radio transceivers are typically less than 2-inch-by-2-inch board modules that fit inside the meters and have power outputs of 100-300mW which at 900MHz translates into possible transmission ranges of 300′-1000′. Currently these transceivers are capable of 17.6Kbps data rates and cost around $35-$80.
There has been considerable discussion regarding the applicability of the newer IEEE wireless specification and their technologies for AMR systems. IEEE specification 802.11, better known as “Wi-Fi,” has limited capability for AMR because of its limited range. However IEEE specification 802.15.4 or ZigBee could have more potential for AMR systems. ZigBee’s operational range is slightly better than Wi-Fi so that it might work effectively in densely populated areas. It is much more likely that these technologies will be utilized in future demand response and home automation applications as AMR and DR systems unite and evolve.
Batteries are another critical issue for AMR systems. If batteries are placed inside AMR meter endpoints where ambient temperatures are high they might fall far short of their expected lifespan and force the utility into a potentially expensive battery replacement program.
Finally some other additional factors to consider with wireless systems are available bandwidth, noise, maximum data rate and path loss.
It’s important to remember that digital communication system products have shorter life spans. These might well be much shorter than the utility’s business requirements. In developing a solid business case for AMR utilities need to envision what they want the system to do beyond the scope of billing cycles and meter reading. These additional initiatives include outage management, disconnect and reconnect functionality, load profiling and demand response. The choice of a robust and reliable communication system is essential to the overall success of each of these initiatives and the overall AMR installation. An AMR project provides a rare opportunity for utilities to create a new path to their customers and premises and this path should be functional, scalable and reliable.
Larry Helwig is a senior engineer specializing in automated metering applications at Nevada Power Company. He has 17 years of experience in utility engineering automation projects, substation and distribution standards and substation design. Helwig is an IEEE member and a licensed Professional Engineer in the state of Nevada and in the province of Ontario. He can be reached at firstname.lastname@example.org.