As an example, consider the simple problem of finding the sum of 36 + 58. Since the sum of
these numbers is greater than 60, the voltages used cannot be equal to the numbers but must
be scaled down. In this case, voltages equal to 1/10 of the numbers will be suitable. The prob
lem setup now looks like Figure 17.
I MEG
AMPLIFIER USED FOR ADDITION
Since the input voltages are equal to 1/10 of the quantities being added, the output voltage will
be 1 /lO o f the sum and so must be multiplied by 10 to obtain the answer. Notice that the answer
is negative with respect to the inputs. If this is undesirable, a second am plifier may be used for
sign inversion. See Figure 18.
The voltages are obtained from the initial condition power supplies and the answer is read on the
m eter. Turn on the FILAMENT switch, after having plugged 1 megohm 1
%
p recision re sis to rs,
previously mounted on 2-prong plugs, into the two input sockets and the feedback socket of
am plifier 1. Plug in a patch cord between the black binding post of initial condition power supply
1 and the black binding post marked METER INPUT which is above the m eter. Connect another
patch cord from the red binding post o f IC-1 (initial condition power supplies will hereafter be
called IC) and the red binding post marked METER INPUT. Set the METER FUNCTION switch
at 10 V and the number 1 INITIAL CONDITION control to extrem e counterclockwise position.
Turn on the HIGH VOLTAGE switch and turn the IC-1 control clockw ise until the m eter reads
3.6 volts. Now unplug the end of the patch cord at the red METER INPUT binding post and plug
it into either of the INPUT binding posts of am plifier 1. In the same manner, connect IC-2 to
the m eter (connect the black binding post of IC-2 to the black binding post marked METER INPUT)
and set the control IC-2 so the meter reads 5.8 volts. Unplug the end of the patch cord at the red
METER INPUT binding post and plug it into the other INPUT binding post of am plifier 1. Set
the METER FUNCTION switch to AM PLIFIER OUTPUT 1 and read the voltage on the m eter.
Multiply this reading by 10 to obtain the answer. CAUTION: In general, before using the m eter
for reading an answer, the METER RANGE switch should be on the 100 V range so as not to
damage the m eter if the result exceeds 10 V. In this case, we knew the answer would be le ss
than 10 V. A lso rem em ber that the output of any am plifier should not exceed ±60 volts.
Since the red binding posts of the IC power supplies are connected to the am plifier inputs, the
input voltages are positive (+).
The output read on the m eter is negative (-) however, due to the action of the am plifier as an
inverter or sign changer. A plus answer can be obtained by use of a second am plifier with unity
gain (Ri = Rf, generally 1 megohm in each case). This is shown in Figure 18.
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