instructions of the manufacturers literature.
Component and cable installation will depend on the
type of system to be installed.
After the cable is installed, check the resistance
with an ohmmeter. Make certain that the maximum
permissible resistance is not exceeded and that there are
no opens, grounds, or shorts.
NOTE: Always follow the installation instructions
that come with each system.
MAINTENANCE OF INTEROFFICE
In general there are four basic steps in intercom
inspect, tighten, clean, and adjust.
Inspection is always of primary importance.
The components in an intercom system are readily
accessible, and, for the most part, can be replaced when
With the solid-state devices of today, all
maintenance programs are basically the same. One of
the first and the most important factors you must take is
to consult the manufacturers recommendations and
guidelines when performing maintenance on any
Common troubles within an intercom system are
normally nothing more than loose connections or
breaks in the cable. If a component should need
replacement, be sure to replace it with the
manufacturers suggested component.
People have used light to transmit information for
hundreds of years. However, it was not until the 1960s
with the invention of the laser that widespread interest
in optical (light) systems for data communications
began. The invention of the laser prompted researchers
to study the potential of fiber optics for data
communications, sensing, and other applications.
Laser systems could send a much larger amount of data
than the telephone, microwave, and other electrical
systems. The first experiment with the laser involved
letting the laser beam transmit freely through the air.
Also, researchers conducted experiments that
transmitted the laser beam through different types of
waveguides. Glass fibers, gas-filled pipes, and tubes
with focusing lenses are examples of optical
Glass fibers soon became the preferred medium for
fiber-optic research. Initially, the large losses in the
optical fibers prevented coaxial cables from being
replaced. Loss is the decrease in the amount of light
reaching the end of the fiber. Early fibers had losses
around 1,000 dB/km, making them impractical for
communications use. In 1969, several scientists
concluded that impurities in the fiber material caused
the signal loss in optical fibers. The basic fiber material
did not prevent the light signal from reaching the end of
the fiber. These researchers believed it was possible to
reduce the losses in optical fibers by removing the
impurities. By removing the impurities, researchers
made possible the construction of low-loss optical
Developments in semiconductor technology that
provided the necessary light sources and detectors
furthered the development of fiber optics.
Conventional light sources, such as lamps or lasers,
were not easily used in fiber-optic systems. These light
sources tended to be too large and required lens systems
to launch light into the fiber. In 1971, Bell Laboratories
developed a small area light-emitting diode (LED).
This light source was suitable for a low-loss coupling to
optical fibers. Researchers could then perform source-
to-fiber jointing easily and repeatedly. Early
semiconductor sources had operating lifetimes of only a
few hours; however, by 1973, projected lifetimes of
lasers advanced from a few hours to greater than 1,000
hours. By 1977, projected lifetimes of lasers advanced
to greater than 7,000 hours. By 1979, these devices
were available with projected lifetimes of more than
In addition, researchers also continued to develop
new fiber-optic parts. The types of new parts developed
included low-loss fibers and fiber cables, splices, and
connectors. These parts permitted demonstration and
research on complete fiber-optic systems.
Advances in fiber optics have permitted the
introduction of fiber optics into present applications.
These applications are mostly in the telephone long-
haul systems but are growing to include cable
television, computer networks, video systems, and data
links. Research should increase system performance
and provide solutions to existing problems in
conventional applications. The impressive results from
early research show there are many advantages offered
by fiber-optic systems.