Page 27 - Analog Circuit Design Art, Science, and Personalities

Analogs Yesterday, Today, and Tomorrow

of models which depended much more directly on the analogies between phenom-
ena as they appear in widely differing physical media. Of main concern here are
those cases in which the modelling medium has been electric, but quite accurate and
articulate models have also been mechanical and hydraulic, and many of these are
hoary with age indeed. Ever since accurate and dependable circuit elements have
been available, and this has been for many decades, notably for resistors and capac-
itors, highly successful passive models have been built for the study and solution of
such problems as those which occur in heat conduction. Dynamic as well as steady
state phenomena may be handled, often in the same model. Again, vibrations have
been studied with direct models having all three kinds of circuit element, plus trans-
formers. Furthermore very large and complete simulative structures, called network
analyzers and based heavily on passive elements, were used in particular for-
though not limited to-AC power distribution and communication lines. Even
today one finds such continuous conductive models as electrolytic tanks still in use
and under development. Many of these tools have specialized capabilities which are
hard to match with the more familiar sort of modem apparatus. The similitude con-
ditions and principles which accompanied and abetted the application of such
models have been carried over to, and guided the users of, the newer computing
means. It should be added that the very demanding doctrines of “lumping,” which
must take place when continuous systems are represented by separate but connected
analog operations, are substantially unchanged as compared to those in passive
models. Here is another branch of knowledge and effort, then, to which we own
recognition as contributing to present day simulation and computing.
From a different direction, in terms of need and application, came another
practical model-building technique which is woven into the analog fabric which
surrounds us today. This one is straight down the simulation highway; we refer to
trainers of the sort used for many years to indoctrinate pilots of aircraft. These
trainers modelled just about everything except nonangular spatial accelerations.
They presented, to a human operator, a simulated environment resembling the real
one in many important ways, as regards his manipulations and the responses re-
turned to him as a consequence thereof. Of course the later counterparts of the first
training aids have become tremendously more refined, and similar structures have
been adapted to other man-machine collaborations, but the inspiration to analog
enthusiasts on a broader scale seems rather obvious. Here was an operative model,
in real time and undelayed, where to the sensory and motor periphery of the trainee the
real environment was presented in a safe and pedagogically corrective atmosphere.
Now it is true that training devices for physical skills are even more numerous
today, and analog simulative equipment finds important applications in these, but a
somewhat extended simile might be in order. For system design in its larger impli-
cations we are all trainees; analog simulation to teach us how a proposed system
might work when at least part of it is new, to guarantee safety if we try out a poor
idea, and to offer peripheral communication at the deliberative level, projects the
trainer concept to an advanced modem setting. The task of simulating the trained
pilot and even the learning pilot, or other human operators, provided a challenge
which has been partly met, and which is still relevant. Simulating the system
designer, as a logical extension, leads as far as you might care to travel.

Things are looking up all over for the analog profession. Substantially every branch
of engineering now applies analog computing equipment: in theory, experiment,
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