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.
