his own ends.
Guided-missile applications are only in the experimental stage,
but another field, that of industrial controls, was already highly
developed before the war and now stands to benefit by the advances
of radar and allied techniques. The devices used are manifold, but
their common purpose is to supply self-correcting means in
industrial processing in place of imperfect manual controls.
A typical problem is automatic register control in the printing
industry. One solution involves the use of a phototube that detects
any misregister and promptly triggers a square-wav ircuit, which
in turn operates a correcting motor. One of these d ices will
control a large printing press at any speed between 300 an 000
feet a minute, and maintain register to within a thousandth
inch at all times.
High-speed photography is also a field in w h microsecond
timing is required. One system uses microflash bul a
control circuit with a period of about two micro-seconds. This
the lower limit: the GE General Engineering and Consulting
Laboratory is reported to have a fully automatic
camera, with a speed of one micro ec , p
finished transparency within 30 seconds; the Navy has anoth
type, utilizing a Kerr cell as the shutter, for which a speed of
microsecond is claimed.
In the development of the atomic bomb, X-ray pho graphs were
made using high-voltage pulses to create peak currents as high a
2,000 amperes, but lasting only a microsecond or so. These devi
are used for observation of machinery in motion, the passag of
bullets through gun barrels, and for the study of motion that n be
re-corded only by microsecond techniques.
Particle accelerators used in atomic research may in o e respect
be considered microsecond devices. Whether the particles move in
linear or closed paths, they must be kicked ahead electrically at the
right in-tervals. At the high speeds at which they move, this
normally involves microsecond timing. In the FM cyclotron, for
example, the particles circle the chamber at the rate of 0.1
d for a single revolution, and the timing of the
g impulses must be of the same order.
example takes us back into the field of radio
nication. It is the system of multiplexing, or sending
l messages simultaneously over a single circuit. Its
plexity is one of its advantages. In military use, for which it
was originally developed, it affords a high order of security
precisely because it involves a complex interlacing of pulses on
which it is difficult to eavesdrop.
The underlying principle, however, is simple. Even the shortest
single sound of speech or music is comparatively long. It lasts for
thousands of microseconds. Why, then, once we have learned how
to divide time into microsecond slices, must we send all of a given
sound over a circuit on which time represents money?Sampling Sections of Sound
All we eed to do is to isten to small sections of the sound for a
fraction a microsecond, and all the information in the original
wave wi e retaine Moreover, by that method we can sample a
number onversa ns or musical r nditions and send them over
e sam cuit si ltaneously.
he m ary on of thi genious system was developed by
ri h. Arm nal Corps, RCA, and Bell TelephoneFro
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