and tenant billing. Processors range in com-
plexity from a microchip in a controller to a
large computer.
Three kinds of processors are used:
local, central, and distributed. With the local
kind, the processor is located in or adjacent
to the device it controls; sensor inputs go to
a signal conditioner and are then fed to the
processor. The central processor receives all
inputs, analyzes the data, and then sends
instructions to controllers located through-
out a facility, allowing coördinated control of
all system elements. In distributed process-
ing, the ongoing decision making is left to
local processors, but a central processor
orchestrates the entire system, with the
advantage that the entire system does not
fail if any one processor does, and only the
local processor has to be reprogrammed to
accommodate changes.
Low-Voltage Control Systems
Low-voltage switching and dimming control is
achieved with low-voltage wires that operate
a relay installed in the luminaire wiring circuit.
The relay is either mounted near the
luminaire or installed in a remote location.
Since the low-voltage wires are small and
consume little electric power, it is possible to
use many of them; they can be placed where
needed without being enclosed in metal con-
duit, except where required by local codes.
With low-voltage switching systems, the
branch circuit wiring goes directly to the
luminaires; this eliminates costly runs of
conduit to wall switch locations. Where
switching occurs from three or more loca-
tions, the savings are considerable. Many
switches can control a single luminaire, or
one switch (a “master”) can control many
circuits of luminaires.
Power Line Carrier Systems
Power line carriersystems (also calledcar-
rier currentsystems) are low-cost, simple-
to-install control systems that operate by
sending a signal through the building wiring
(“power line”). The switch functions as a
transmitter that generates the signal. A
receiver located at the luminaire or electric
appliance turns a circuit on or off when it
senses the appropriate signal.
As long as the transmitter and the
receiver are connected to the same electric
service in the building, no control wiring is
required. Any number of luminaires can be
attached to one receiver or to any number of
receivers; any number of transmitters can
control any one receiver. Great flexibility is
inherent in this kind of system.
Power line carrier systems are subject to
malfunction, however. Automatic garage
door openers and communication systems
in airplanes flying overhead may operate on
the same frequency as the power line carrier
system, causing luminaires and appliances
to turn on and off when unintended.
Existing wiring systems in older buildings
can significantly reduce the effective range
of communication between the sensor, pro-
cessor, and controller. Additionally, the over-
all capacity and speed of this kind of system
is limited.Energy Management Controls
In offices of the past, lighting controls were
used to provide lighting flexibility. Today,
their major application is energy manage-
ment. Simple controls, such as photocells,
time clocks, and occupancy sensors will
automatically turn lights on when needed
and off when unnecessary. For larger facili-
ties,energy management controlsystems
are designed to integrate the lighting with
other building energy systems such as those
used for heating and cooling.
The key to proper application of these
controls is not only the selection of the
proper control device, but also the careful
planning of where and when the control isELECTRICITY