I MEG
-AAA/VH
I MEG
' M A A A A H
I MEG
I MEG
■AA/VW
I MEG
AAAA/V
Figure 18
AMPLIFIERS USED FOR ADDITION AND INVERSION
MULTIPLICATION
Multiplication by a constant is perform ed by using different values of input resisto r and feed
back re sisto r. A s an example, find the product of 10 x 37. See Figure 19. Plug a 100 K, 1%
p recision resisto r into either input socket and a 1 megohm re sisto r into the feedback socket
of am plifier 1. Set IC-1 to 3.7 volts and then connect this voltage to that input o f am plifier 1
to which the 100 Kf2 re sisto r was connected. Read the output on the m eter and multiply this
reading by 10 to obtain the answer. (The 37 was divided by 10 in order to keep the result under
60 v o lt s .) Again notice the result is negative with respect to the input, due to the 180 phase
shift in the am plifier.
I M t o
e0=-Bf- g - I,OOP,OOP C3 7 VOLTS) =10X 3.7 VOLTS
RI
'
100,000
Figure 19
AMPLIFIER USED FOR MULTIPLICATION
INTEGRATION
It was shown on Page 10 that by replacing the feedback re sisto r of an am plifier with a capacitor,
the output of the am plifier is proportional to the integral of the input voltage, or m ore s p e c ific
ally,
e = — —J — I e : d t + e j c
°
Rjtf J
1
,c
Plug a 1 megohm precision resistor into either of the input sockets and a 1 pfd mylar capacitor
into the feedback socket of am plifier 1. When using an am plifier as an integrator, it is n e ce s
sary to rem ove the charge on the capacitor before using the am plifier again. If this is not done,
an e r r o r will be introduced in the next solution due to this residual change. In the E C -1, this is
accom plished by connecting a pair of the relay contacts a cro ss the feedback capacitor; the con
tacts are closed when the am plifier is not integrating and open when the computer is operating,
as shown in Figure 20 on Page 20.
Page 19
