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 (). 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.