where
\i
is the ratio of the voltage e0 appearing a cro ss the potentiometer to the voltage
a cro ss the arm of the potentiometer and ground.
R f
Thus p e_ = — - — e i
°
R:
and
e_ =
—
®
Thus division by
\i
has been accom plished if R f/R f is made unity (Rf = Rf = 1 megohm, for
example).
Since p is less than unity, a scale factor must be introduced when dividing by numbers larger
than one. Let the desired divisor be 2.5. The value chosen for p. would then be 0.25, since p is
less than one. The indicated result (answer) w ill then be greater by a factor of 10 than the true
value of the answer, so the indicated answer must be divided by the same value as used in r e
ducing the division to a value of less than one (in this case 10). Thus, for this example
®o
0.25 1 10
1
Rj "i
since
2.5 = 0.25 x
10
choosing
R
j
=
r
. =
i m e g
,
this becom es
1
/ 1 x
eO -
0.25 *10' e i
which becom es
10
« 0 —~ q
25
*■
If the divisor had been 25, a factor of 100 would have been chosen, yielding
100 ®o
o.25 *■
and the indicated result would be divided by 100. If the division is less than unity, no correction
is necessary.
Again making use of the approximation e „
=
o, it is possible to show the operation of the am pli
fie r as an integrator. The feedback re sisto r is replaced by a capacitor, as shown in Figure 8
on Page 10.
Page 9
