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T h e p o t . e n t i o n e t e r n a y b e u s e d i n c o n j i r n c t i o n w i t h r e f e r e n c e t o
obtain a fixed
accurate voltage
less than reference,
or to nultiply
a problen variable
by any constant less than unity.
Figure 2.4-L is
a schenatic of a potentiometer
with +100 volts
applied to the higlt
endtt, where K is;
P r
K =
'"t
(EQ.2./+-1)
R1
T h e p o t e n t i o m e t e r s h o r n r n i n F i g r r e 2 . / + - 5 i s r r r r l o a d e d , a r r d t h e
mechanical rat,io of R1:R1 equals the
electrical
ratio
ee:ej3i
thus,
t h e p o t e n t i o m e t e r n a y b e s e t t o t h e e x a c t r a t . j - o b y n e a n s o f t h e c a ] . i .
brated dial
attached to the wiper shaft.
However, the two ratios. will
n o t b e e q u a l w h e n t h e p o t e n t i o m e t e r i s l o a d e d a s i s t h e c a s e w h e n i t
is used as a computer problem element.
Norma11y, the pot is loaded by
either
a lM or locK ohn resistor
since a potentioneter
generally
feeds
a n a m p l i f i e r a n d t h e s e v a l u e s a r e t h e m o s t c o m m o n a n p l i f i e r i n p u t r e -
s i s t o r s . F i g u r e 2 . / . - 3 i l l u s t r a t e s t h e e f f e c t o n t h e e j f , } : e o a n d . R 1 l R 1
ratios
r,rhen the potentiometer
wiper feeds a lOOK 1oad"
In order to eleminate the effeets
of loadingo it
is more conirenient
to set the poteniometers r:nder actual load and
monitor the miper voltage
)+ The high end of a potentiometer
refers
to the termination
of the ?re-
located
at t.he top of the schernatic designation
of the Pre.?atch
panel.
The low end is the botton terminatibn,
nonnally
gror:nded ex-
cept in the case of t'he ungrounded potentiometer'
t
r
r
r
t
J
(
(
(
I
I
I
I
(
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