[Technology Report]
A Measure Of Opportunity Awaits In Electric Meters
Move over consumer and telecom worlds. Recent developments turn electric metering into an unexpectedly fertile field for engineers of all types.
Besieged by conservation issues, utility metering is undergoing somewhat of a renaissance—particularly electricity metering. That's because electrical distribution systems everywhere are fragile. Metering used to be the nearly exclusive domain of EEs with a power specialty. Today, it's wide open to chip, board, and system designers, as well as software writers.
The reluctance-motor electrical-meter movement is more than 100 years old. Now, it's getting displaced by chips that aren't just cheaper and more precise, but also can separate the active and reactive components of power and provide gateways to remote reading.
The metering business resembles the automotive business. While relatively few players dot the landscape, they're wide open to innovations that will give them positioning with the utilities that comprise their market. Also, like automobiles, once you've sold a chip or technology into a product, it represents high-volume sales over a long end-product life cycle.
One example of the new kind of residential meter hangs in the service entrance to my own house (Fig. 1). When we put in solar panels last summer, the contractor helped us negotiate new electric rates with the power company. We're charged for electricity we use, or credited for electricity we generate, at approximately 28 cents/kWh during peak hours. During non-peak hours, the rate goes down to 7 cents. The meter keeps track of both figures, and we settle up once a year.
The photo shows a port on the meter for rapid reading. With it, our meter reader needn't wait for the LED panel to cycle through five displays, but that's pretty low-tech. The trend is toward remote reading, which opens up many possibilities. RF drive-by reading has been used for some years. But it's becoming more sophisticated, with newer wireless technologies generating faster and more secure uploads.
SUBMETERING Every utility customer needs at least one electric meter. But many people don't realize that there's really high volume potential in submetering—meters that users purchase to read their own electricity usage.
Submetering was once mainly the province of apartment buildings. Where allowed, building owners would negotiate an industrial contract with the electric company and bill tenants on their actual energy usage. More recently, submetering has become important to large manufacturing companies.
It shows managers how a site's total energy consumption is distributed among the various departments, tenants, or processes within the building or facility. Also, it helps businesses with peak-shaving, load-shedding, aggregation, and other measures that lead to lower energy bills.
Of course, management has to know what to do with the data. There continues to be an opportunity to refine and simplify data collection and storage, as well as the user interface that enables people to display and manipulate data and manage the systems that use electricity.
One example of a medium-sized player innovating in the sub-metering business is a Swiss company, LEM. Its Wi-LEM system lets users create inexpensive, reconfigurable ZigBee-based submetering systems. Assembly takes little more effort than clamping current probes around power leads and mounting the Wi-LEM hardware. The system consists of energy meter nodes (EMNs), mesh gates (MGs), and mesh nodes (MNs).
Each EMN attaches to the electrical wiring for the system or machine it's monitoring with split-core transformers. The EMNs measure active and reactive energy, maximum current, and minimum voltage at 5- to 30-minute intervals. The MG is a standalone ZigBee gateway that manages its EMN network, which is a wireless mesh configuration. Any MG can manage up to 240 EMNs while storing the latest data from its network.
Because communication between an EMN and MG is usually limited to a 25-m line-of-sight range, LEM offers MNs, simple repeaters that extend the network's range as much as necessary. Between a local mesh of EMNs and more remote EMNs communicating through MGs, users can build systems that cover an entire manufacturing center or residential facility.
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