Power Line Communication Frequently Asked Questions
What makes power lines a cost-effective media for networking devices?
Power line communication uses the existing power lines within a home,
building or an outdoor power distribution network to transmit data from
one device to another. With a well-designed power line solution, devices
should be able to communicate using the existing wiring infrastructure,
without any rewiring or modification. This makes power line communication
one of the most cost-effective means for networking devices.
What kinds of applications can be enabled by communications over
power lines?
Any electrical devices connected to the power line can be networked to
communicate with each other. Some examples of applications include:
-Intelligent electricity meters: This solution enables utilities to network all
of their electricity meters and to read them from a remote central location (Automated
Meter Reading). A Power Line Smart Transceiver-based meter can also enable utilities
to remotely switch on/off power to a facility as well as detect any tampering
of meters or unauthorized power consumption. Echelon's power line technology
is currently being deployed in 27 million meters in Italy by their largest utility:
ENEL.
-Networked home appliances: Every device in a home can now communicate with each
other as well as with the local electricity meter. These devices could include
the refrigerator, washer/dryer, AC/heating, lighting system, security system,
pool heating, etcetera. As a result, utilities and consumers can monitor and
manage power consumption more effectively (Demand Side Management) thereby increasing
cost savings and convenience.
What are the challenges associated with communicating over power
lines?
Power lines were designed to carry power and not data. This means it takes a
very sophisticated transceiver to reliably communicate over power lines. Many
electrical devices connected to the power lines adversely impact the data that
is being transmitted. The quality of the signal that is transmitted over power
lines is dependent on the number and type of the electrical devices (televisions,
computers, hair dryers, etc.) connected to the power lines and switched on at
any given time. The quality of the signal is also dependent upon the wiring distance
(not physical distance) between the transmitter and the receiver as well as the
topology (wiring architecture) of the power line infrastructure in the home/building.
All of the above impediments could vary between buildings, neighborhoods, and
the power grids in various countries, making a universal solution even more challenging.
What is Echelon's background in this area?
Echelon has been a pioneer in power line communication technology since the
1980s and currently holds 38 patents for technical innovations in the field
of power line signaling. Most power line solutions adopt either spread spectrum
or narrow band technologies for communications. Echelon has fielded products
based on both technologies. Our first generation power line solutions were based
on spread spectrum technology. We have since then migrated to a more robust,
economical, and unique narrow band technology with dual-frequency operation.
Spread spectrum power line solutions were found to be much less reliable in
most cases. See the PL 3120
and PL 3150 Power Line Smart Transceiver datasheet for more details on
other features unique to Echelon's power line transceivers.
What do I need to look for in a power line communication solution?
In the case of power line transceivers, a side-by-side analysis of product
specifications may not yield much information about their reliability. Two
transceivers with the exact same specifications may have completely different
performance characteristics. The only meaningful and effective method of evaluating
a power line transceiver is by actually testing its performance in the target
environment. Nevertheless, there are a few key characteristics that one should
look for:
1. Total number of components required for a complete communication
device and the total cost associated with it. One must also factor in
the need for external microcontrollers, memory, filters, or amplifiers.
The cost of implementing the appropriate power supply is also a very
important factor to take into account when evaluating various power line
solutions.
2. The frequency spectrum it uses for communication and its compliance with
regulations. This is particularly important to ensure a common networking platform
that you could develop and implement in products you ship worldwide. Europe
already has very stringent regulations in place for power line communications,
while other countries in North America, Asia, Africa and Australia are pursuing
similar restrictions.
Note: In Europe, power line signaling must be confined to the 9kHz - 148.5kHz
frequency range. This spectrum is further divided in to "bands" and
allocated for specific applications, as follows:
· A-band: 9-95 kHz for electricity suppliers
· B-band: 95-125 kHz for consumer use without protocols
· C-band: 125-140 kHz for consumer use with the CENELEC protocol
· D-band: 140-148.5 kHz for consumer use without protocols
· Above 148.5 kHz: power line communications prohibited
Using the C-band (with the CENELEC protocol) for in-home communication
ensures that only one device communicates at a time thereby minimizing
collisions and improving communication reliability. The B and D-bands,
although legal for in-home communication, are more prone to collisions
and interference from other solutions operating in this band. These bands
are more suitable as alternate / secondary communication bands that may
be used when the C-band is blocked by noise. The CENELEC protocol is
already implemented in Echelon's power line transceivers, eliminating
the need for users to develop the complex timing and access algorithms
mandated under CENELEC EN50065-1.
3. Communication performance in the presence of the "noisy" appliances
such as low-voltage halogen lamps, computers, printers, fax machines, hairdryers,
etcetera. Note that some television sets induce very high levels of signal distortion
that could make it impossible for some receivers to decode the transmitted signal.
4. Requirement for "conditioning circuitry" or other wiring
modifications that would require the services of a professional electrician
and therefore add costs. This includes:
-Phase couplers required by some solutions to ensure communication between sockets
on different phases in a home with multiple phases.
-Wiring modifications to support "switched-leg" circuits. A "switched-leg" circuit
is a common wiring architecture used to wire lamp switches in many parts of the
world including the US, Australia, New Zealand, etcetera. See Q&A on "switched
leg" circuits for more details.
5. Availability of easy-to-use tools for testing the performance of
the transceiver in the target environment prior to investing in any development
effort.
6. Availability of comprehensive support documentation that describes in detail
every stage of the design-in process including recommendations on system architecture,
power supplies, and coupling circuit design.
7. The types of applications and the number of actual deployments (not
pilot projects) in the field using the technology.
What is a "switched-leg" circuit?
A "switched leg" circuit is a common wiring architecture
used to wire lamp switches in many parts of the world. In this architecture
the neutral is routed through the ceiling lamp and there is no direct
neutral connection at the switch. See diagram below. "Switched
leg" circuits are common in many parts of the world including Australia,
New Zealand and the U.S.
In such circuits, an "intelligent" switch that can communicate
with the lamp over the power lines faces multiple challenges. The switch
must be able to power the transceiver and communicate with the lamp switch
ON. Secondly, it should be able to power the transceiver and communicate
with the lamp switch OFF but without lighting the bulb. It must also
be an extremely compact design with a small, low-cost power supply to
ensure that the required components fit into a typical junction box.
Echelon's power line technology was designed to overcome these challenges,
making it feasible to embed the technology into cost-sensitive light
switches that can operate anywhere in the world.
