Any variations in voltages in any part of the circu it of a direct-cou p led am plifier cause v a ri
ations in the output voltage which in turn introduce e r r o r s in the solution. With constant input
the output will vary, resulting in "d rift” , which in creases with am plifier gain. This introduces
a paradox since, as has been shown, e r r o r is reduced by increasing am plifier gain but this in
turn in creases drift which in creases e r r o r s . For this reason, very high gain am plifiers gener
ally use some means of stabilization in ord er to reduce drift. *
READ-OUT
For arithm etic problem s in which a single num erical answer is obtained, the result can be read
on the m eter. In problem s having a continuous solution (changing with tim e) an o scillo sco p e is
desirable. It is possible in this case to watch the effect on the solution of varying the various
problem param eters. This is especially true when repetitive operation is used. In this case
one of the computer am plifiers is used to provide the sweep. The o scillo sco p e must be a DC
scope.
If a permanent record of the solution is desired, a photograph of the o scillo sco p e trace may be
made or a recording galvanometer may be used. Examples of both methods are shown in the
illustrative problem s.
NON-LINEAR OPERATION
A discussion of non-linear operation is beyond the scope of this manual. An excellent treatment
of non-linear operation can be found in ANALOG COMPUTER TECHNIQUES by Clarence L.
Johnson, Chapter 7, Pages 107-127.
CIRCUIT DESCRIPTION
DC OPERATIONAL AMPLIFIER
The general requirem ents for a DC am plifier for computer use are high gain, high input imped
ance, low output impedance, good linearity and stability (low drift). The circu it of the am plifier
used in the Heath Analog Computer is shown in Figure 12.
+ 300 VOLTS
Figure 12
DC OPERATIONAL AMPLIFIER FOR EC-1
* Korn and Korn, ELECTRONIC ANALOG COMPUTERS (M cGraw-Hill Book Company, Inc. ,
New York, 1056) Second Edition, Pages 191-196 and 231-239.
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