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POWERLINE
COMMUNICATIONS OVERVIEW
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The PLC-1 transceiver is a digital Integrated Circuit (IC) implementing a half-duplex transmitter/receiver function for Power Line Communications (PLC). The IC includes a complete set of high-level functions, enabling designers to easily implement high-performance PLC networks. |
PLC is an essential technology for HA, because it enables the installation of a
control-oriented communication network without the need to tear down walls in
order to install dedicated wiring. PLC is less expensive than IR and RF
solutions. Moreover, the PLC-1 technology itself resolves all the difficulties
associated with networking. OEMs can easily and rapidly design powerful products
with the PLC-1 technology because the PLC-1 IC includes a complete set of
powerful networking functions, relieving the designer from low-level tedious
networking details, and offering powerful networked-products to the end-user.Powerline Carrier (PLC) is a communication technique that uses the existing power wiring (120 Volts, 240, etc…) to carry information. A "wireless" means of communication, PLC technology supersedes the installation of dedicated wiring.
PLC can convey analog information (e.g., voice in a PLC intercom) or digital information (e.g., data or control information in a Home Automation system).
Implementing
high-level networking functions, the PLC-1 is a digital transmitter and
receiver Integrated Circuit, or "transceiver IC" for
short, that superimposes digital information (i.e., bits) over the electrical
power flowing through the wiring of a house or building (see the figure on the
right).
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- Low Baud rate (sometimes under 0.05 bps), long distance (1 mile or more) PLC systems include such applications as data communication over common 25 kV power-distribution grids operated by power utilities.
- Medium Baud rate (generally in the 0.050 to 50 kbps range), medium distance (typical practical range under a few hundred feet) PLC systems include control applications, such as intra-building communications (Home Automation, lighting control, Automatic Meter Reading applications, etc.). The carrier frequency typically lies between 50kHz and 535 kHz.
- High Baud rate (100 kbps or more), local area PLC systems include data intensive applications where very low cost is not a critical factor, such as Internet access, printer or file sharing, computer networking, etc. The typical low-amplitude carrier frequency is high, between 1.7 and 30 MHz.
The Metricom PLC-1 is a type B technology used in cost sensitive, medium Baud rate applications. These include Home Automation, lighting control, remote control, etc.
LIGHTING CONTROL
PLC-1 enables lighting control in existing homes or buildings. Replace wall switches and dimmers with PLC communicating switches or dimmers. These devices receive PLC commands that turn them on or off, set them at given light levels, etc. Different controlling devices send commands to PLC-enabled wall switches, from HA controllers or manual keypads to PCs. A standard Web browser may also be used to control and program lighting functions over the Internet.
If these products communicate both ways (bidirectional communication), switches and dimmers can report the power level of the load under control (on/off, actual level, etc.) or any other internal variable. Set up your devices in predefined groups and control each group with a single command, e.g., group exterior lighting.
When you activate your wall switches, they too can transmit PLC messages. You could, for example, push a switch before leaving home and set the whole house in unoccupied mode, turning off all lights, triggering the security system, activating random light patterns to simulate your presence, adjusting temperature set points to save energy, etc.
ACTUATORS: THE BASIS OF HOME AUTOMATION
PLC
wall switches and dimmers are specific form factors
of what we will call "actuators." PLC-controlled electrical
outlets are also an important HA actuator. Like wall switches, these
devices include one PLC-1 IC, are unidirectional (receive-only) or bidirectional,
are designed for either 120V or 240V operation, etc.
The
same basic outlet-controller may be packaged differently and becomes a plug-in
PLC controller. This device plugs into standard electrical outlets along
with the controlled load. A lighting-control PLC relay
(installed inside a fixture or ceiling junction box) is yet another example of
the same basic product re-packaged in a different form. For
commercial/industrial remote control, an eight-relay
output-control module might be designed and installed inside lighting
control panels. Etc.
Actuators are, generally, simple devices and include a small amount of intelligence. As the basic components of HA and industrial/commercial PLC control, actuators must be low-cost. Unlike other popular PLC products, PLC-1 actuators may include analog functions. For example, line-voltage communicating thermostats use PLC-1 to convey set-point and actual room temperature information.
We define actuators as simple analog and/or digital output modules. Lighting control actuators (switches, dimmers, etc.) and general purpose actuators (relays, plug-in modules, etc.) do not include time clocks-though an essential function in lighting control-nor any complete TCP/IP stacks and modems for internet access. Yet, we want the lighting functions of a given HA system to be remotely accessed, controlled, and programmed through the Internet. Thus, actuators are generally designed as simple, low cost devices and execute PLC commands transmitted by one or many intelligent controllers.
SENSORS
Sensors,
the second most important devices in control applications after actuators,
measure a physical quantity and transmit this value over the PLC network.
Transmission conditions may differ from one sensor or one application to the
next. Some sensors will not transmit without first being polled, some transmit
only when their input changes beyond a given threshold, others transmit at every
t time unit, etc. The most common sensors are the binary
sensor, i.e., a switch, and the general-purpose analog
sensor used for temperature, light level, pressure, and other such
applications.
PLC-1
is a general-purpose data transportation IC and, unlike other PLC technologies,
can convey sensor-type information. Typical system architectures implement
sensors and actuators as simple input/output devices. 
However, a
thermostat,
for example, can also act as a sensor and broadcast a temperature measurement
that other controllers or actuators will then use. Passive Infra-Red (IR)
sensors can also trigger lights in a given room and activate the alarm system if
the house system is set in the unoccupied mode.
REMOTE CONTROLS
Actuators and sensors, defined in the previous paragraphs, include analog and digital units such as: wall switches, wall dimmers, electrical outlets, plug-in modules, relays, temperature sensors, thermostats, etc. These devices contain one PLC-1 IC and can receive commands from one or more controllers. Bidirectional devices are fully networked and may transmit data. Sensors and actuators are to be considered as "wired" by PLC.
Some sensors and actuators might support certain control functions, but these devices are, generally, neither very intelligent nor sophisticated. In many situations therefore, a controller will drive them. One of the most elementary forms of control is manual control.
A simple PLC keyboard-display, plugged into any electrical outlet, enables you to control lighting, various loads, (e.g., coffee pot, lamps), temperature (pool, thermostat settings, exterior, etc.), and several other devices from anywhere in the house. For example, before going to bed, you will push the "all lights off" button on the keyboard. A given house may contain any number of keyboard-display units that are simply plugged into electrical outlets.
This form of control is not "Home Automation" since it is not automated. It is only Remote Control, but is already a very convenient application for several users. Remote Control functions may be set with a hand-held IR (Infra-Red) remote control device that uses an IR to PLC interface. A touch-tone phone may also serve this purpose: imagine the convenience, for example, of calling the country house to raise the temperature before you arrive! Remote control can also be achieved via the Internet, using a standard Web browser. Communicate with your house, say (http://www.george.smith.house.ca), and control and program all house functions!
SCHEDULING
Programming events at pre-determined moments is one of the most basic HA features. A time clock scheduler is a good example of a simple HA controller. This controller can turn lights on and off, lower or raise the temperature at night or during work, set home temperature at normal levels before you return from work each day, cycle the pool pump, start the coffee pot, etc.
And which controller implements the schedule? In its simplest form, we might have a simple programmable time clock similar to an alarm clock. In more sophisticated installations, this function is usually integrated into the HA controller.
BASEBOARD HEATING SYSTEM
Millions of North American dwellings use baseboard heating. This system involves one baseboard heater per room, controlled by a single wall thermostat. Thermostats average at eight per dwelling. One disadvantage of this heating system is that users cannot easily set back their thermostats to save energy. You may not want to visit eight thermostats before going to bed, leaving for work, coming back from work, or leaving on weekend vacations. You may not want to install eight individually programmable thermostats…for obvious reasons.
PLC-1
can help: replace standard thermostats with communicating electronic
thermostats. What's the result? A net increase in comfort
and excellent energy savings, for starters. You
will thereafter control the temperature setback from a single convenient
control-point and payback usually occurs within
less than 2 years.
Each room thermostat remains completely independent, measuring and controlling temperature in only one room. Yet, all thermostats receive their set points in the form of a PLC message, unless a given unit is returned to a different set point by a local command.
Which system effects the set-point change? The HA controller or a general scheduler does the job and, in simple installations, the scheduler may be one of the eight PLC thermostats! In this case, look at the system as composed of one simple programmable-thermostat driving the other thermostats in the house.
AUTOMATIC METER READING
What is Automatic Meter Reading (AMR)? It is the remote collection of consumption data from your utility meters and it makes use of telephony, radio frequencies, power lines, and satellite communication technologies to move around its information. AMR enables water, gas, and electric utility-service companies to increase operational efficiency, improve customer service, reduce data-collection costs, and quickly gather critical information that provides needed insights to company decision-makers.
Utilities may use PLC-1 to upload meter data to a pole-mounted concentrator, linked to the utility's host system. Variable rate information may be downloaded in the opposite direction, enabling Demand Side Management and resulting in savings to customers. AMR systems that use other communication links can use the PLC-1 to transfer messages into customer's homes, either from a concentrator or directly from the utility's meter. Utilities can monitor and control Internet-enabled systems over the Internet.
PLC-1 AND HOME AUTOMATION
The Home Automation Association puts forth the following definition for HA:
"Home Automation is defined as a process or system (using different methods
or equipment) which provides the ability to enhance one's lifestyle, and make a
home more comfortable, safe, and efficient. Home automation can link
lighting, entertainment, security, telecommunications, heating, and air
conditioning into one centrally controlled system."
Although many will not endorse the "one centrally controlled
system" concept-as opposed to decentralized systems - it is interesting
to note that, according to this definition, an HA system links different
home subsystems, e.g., lighting, entertainment, telecommunications, etc., that
might otherwise be unrelated. Metricom believes this definition should emphasize
that "automation" essentially means control, and consequently that
"Home Control" is an equivalent concept.
HA is different from Home Networking, the latter being dedicated to data
communication. It is true that HA may use one or more networks to link devices
and sub-systems, but this control network is still physically different from
data networks. HA networks are designed to carry very small amounts of control
information, while data networks are designed to carry large amounts of data,
generally at the highest possible speed. HA networks may be built from
low-voltage dedicated wiring, e.g. twisted pair, or may use the home's existing
wiring: power lines. A third option is a wireless network: IR or RF.
PLC is an essential technology for HA, because it enables the installation of a
control-oriented communication network without the need to tear down walls in
order to install dedicated wiring. PLC is less expensive than IR and RF
solutions. Moreover, the PLC-1 technology itself resolves all the difficulties
associated with networking. OEMs can easily and rapidly design powerful products
with the PLC-1 technology because the PLC-1 IC includes a complete set of
powerful networking functions, relieving the designer from low-level tedious
networking details, and offering powerful networked-products to the end-user.
Some day in the near future, our
houses will be permanently connected to the outside world with a broadband
digital-communication channel, carrying TV and video signals, music, radio
programs, phone conversations, faxes, emails, Internet data, electronic
newspapers, and so on. Gradual evolution will lead to this revolution.
The next logical step of this digital-age home-communications revolution is a permanent
Internet connection (at medium bandwidth). Our homes, that today for
the most part have their very own phone number, will eventually have a specific
IP address (http://john.smith.home.ca). This simple
connection will probably use the existing phone-wiring infrastructure in its
original setup and will enable the first generation of a whole range of new
products and to-our-home services. An electronic notepad installed on the
refrigerator door, already available web TV devices, web phones, all these
low-cost devices will use the permanent, to-the-home connection. Expect to send
and receive e-mail and voice messages, phone conversations, and access new
Internet services (local shopping, pizza orders, banking, etc.) via this
first-generation network.
The same infrastructure will support security monitoring and burglar and fire
protection. Electric, gas, and water utilities will remotely read their
respective meters and offer new services to their customers, such as time-of-use
rates, energy management services, electronic billing and payment, etc.
Where does PLC-1 technology come
onto this scene? PLC-1 is a natural in-home extension
of the global to-the-home communications network. PLC-1 readily links
to the Internet, today, using existing embedded Internet technologies (See embedded
internet). Electric meters, along with other in-home devices (thermostats,
lighting controllers, intelligent appliances, security systems, etc.), will not
be equipped with a direct connection to the outside world; because of cost and
security reasons; a home gateway (currently in development: see osgi.org)
will be used. PLC-1 allows you to build a local "wireless" network,
including different devices (utility meters, thermostats, switches and dimmers,
HVAC systems, appliances, etc.) and thus an all around HA controller that will
extend Internet ubiquity.
Any device connected to the PLC-1 network is accessible from the Internet,
through the gateway. PLC-1 is the last segment of a communications network that
enables utilities to communicate with their meters, users to remotely access and
control house functions, appliance manufacturers to remotely download their
latest software options or do remote diagnostics, and HA controllers to
implement useful control functions.
You have previously seen several examples: PLC-1 products show near limitless variety and scope in their diverse application domains:
- Line voltage thermostats : slave thermostats, master thermostat.
- Wall switches.
- Wall dimmers.
- Electrical outlets: dimming, non dimming.
- PLC relays : plug-in, screw-in, junction box, ...
- Remote sensors: temperature, light, etc.
- General remote analog/digital I/O.
- Keypad-display.
- IR to PLC.
- RF to PLC.
- TP to PLC.
- General scheduler-timers, programmable time clocks, etc.
- PLC access from a Personal Computer.
- Home Automation controllers.
- Telephone interface.
- Low-cost, residential lighting control.
- Industrial/commercial PLC control.
- Automatic Meter Reading products.
- Internet access and control.
- Home Networking products.
