hese meters monitor, analyze, and store information on energy usage. Because many utilities
promote off-peak consumption, there may be several defined time segments for different energy
costs. Therefore, not only total energy consumption is tabulated, but also energy consumption
during each of several time segments.
A network connection between meters allows a centralized data collection. This becomes a
significant advantage due to the economics of labor-intensive manual meter reading, especially
as both the number of installed meters and the cost of labor increase. Networked automatic
meter reading (AMR) systems further reduce problems with safety and security, as human
access to distributed meters is less important. Installation costs may also be lower, as
networked meters have more flexibility in terms of possible locations.
The architecture of the connecting network can be one of several types; a bus, a daisy-chain, or
a tree structure are examples. One of the more efficient architectures in terms of interconnection
is the bus architecture. Each meter attaches to the main bus through a stub, which is kept as
short as possible. Signals on the bus are available to all the nodes. Typically, a master node
controls the communications on the common bus, indicating when each node has permission to
transmit.
The information that must be communicated to and between meters includes set-up, energy
usage, and diagnostic data. Set-up data is communicated to a meter during initial installation,
after a repair, or when tariff or time segment data must be updated. Energy usage data is
collected from each meter on a periodic basis, and may include the power, voltage, and current
data for a set of time segments, as well as peak, average, or other statistics. Diagnostic data
may be communicated to indicate not only samples of the state of the distributed power, but also
the state of the meters themselves.
There are several choices for communication with meters. One popular method is through a
twisted pair of wires, using RS-485 differential signaling as defined by the TIA/EIA-485 and ISO-
8482 standards. This method has the advantages of high noise immunity, fast signaling rate,
many nodes on a single bus, and a wide base of proven transceivers available. Other methods
include various wireless technologies, signaling over the power lines, and local infrared (IR)
links. Because of its advantages, this application report focuses here on the 485-based
solutions.