CIRCUIT DESCRIPT ION
MODEL
1 5 3 MI CROVOLT - AMMETER
d .
Re s i s t o r Rl0 2
and neon lamp
GLlO l
in
the
input
c i r cu i t p r ov i d e
ov e r l o a d pro t e c t i on
f or l l l e
v o l tme t e r .
T h e
inpu t a l s o i n c l u d e s
a
s y s t em f o r
i n c r e a s i n g
t h e
s p e e d o f mea s u r e
men t s f r om h i g h
s ourc e
i mp e d a n c e s b y d r iv i ng c a p a c i t or
CI0 2
f r om
t h e f e e d b a c k s i g na l .
c .
Th e d e
i n p u t s ig n a l
i s com" e r t e d t o a n a c s ign a l
b y p h o t o - mo d u l a t o r s
ElOl and
E I0 2 .
T h e
p l l o t o - mo d u l a t o r s a r e s p e c i a l l y
d e s i g n e d f o r h i gh i n pu t
r e s i s t a n c e a n d l ow
o f fs e t .
Lu c i t c
r o d s
a r e u s e d
t o
cond u c t t h e
l
i
g
h
t
f r om l
a
mp
s
ElO I B
a
n
d
E 10 2B
t o
t h e
c e l l s
t o
r e
d u c e t
h
e
d r i v e s ig n a l
through t h em .
f .
Th e
inpu t
f i l t er a n d p ho t o - m o d u l a t o r a r e hou s e d in a
s e p a r a t e
c
o
m
p
a
r
t
me
n
t t o s h i e l d
and i n s u l a t e
t h e s e
c i rc u i t s .
4- 3 .
ANPLI F I ERS .
a .
T h e a c s i gna l f r om
t h e ph o t o - mod u l a t o r
i s
amp l i f i ed
b y a 5- s t a g e
a c
a mp l i f i e r and
d emod u l a t e d to
d c .
b .
Tt e a c amp l i f i e r
u s e s
l ow- n o i s e
d e s ign
w i t h f ixed
b ia s
and l ow
p l a t e
v
o
l
t
a
g
e on t h e
f
ir
s
t
t�o
amp l i f i e r s t age s ,
V IO lA
and
V I02A .
The
f our th amp l i f i e r
s t a g e
u s e s a
f r e q u e n c y
s e l e c t ive tw i n - T f i l t e r tuned t o t h e c a r r i e r
f r eq u ency
t o r e d u c e
n
o
i
s
e
a n d
t o r
e
d
u
c
e
t h e
modu la t i on
p r o d u c t s
and b e a t s a s s o c i a t ed w i t h
t he
mod u l a t ing
a c t i on .
Re s i s t or s
R 1 4 5
t o
R l 5 3
are
s e l e c ted wi th
the
RANGE
Swi t c h and a r e u s ed
i n the c i r cu i t
t o
vary
t h e
amp l i f i er
g a in a s
t h e
rang e s are chang e d .
Thi s
m
a
i
n
t
a
i
n
s
an
a p proxima t e ly cons t a n t
f e edb a c k
f a c t o r
o n
all
b u t t h e mo s t
s ens i tive
rang e s .
c .
Th e
o
u
t
pu
t
o f the a c
a
m
p
l i f
i
e
r
i s a p p l i e d
t o
pho t o -mod u l a t o r
E I0 3
a n d c onv e r t e d t o
d e .
The
s i gna l
i s f i l t e red
b y
c a pa c i t o r
C 1 20
and
res i s t or s Rl 2 6
and R1 28
t o R1 30
t o
re
d u c e
the
carrier s igna l appearing
o n
the ou tput . ,
4- 4 .
C
AT
H
O
D
E FOLLOWER .
T
h
e
f i l tered d c s ign
a
l
i s app l i ed
to
the
c
a
t
h
o
d
e
f o l l owe r ,
t
ub
e
V I0 3B ,
an
im
p
e
d
anc
e
trans f ormer whi ch
p
r
ovi d e s a I-vo l t ,
I-mi l l i amp ere outpu t .
T
h
e
outpu t
a l s o
s
upp
l
i e
s the recorder ou tpu t ,
m
e
t
e
r
and
f e edback
network .
4- 5 .
FEEDBACK
NETWORK.
a .
The
feedback ne twork , c ons t ru c t e d
of
a c cura t e s tab le r e s i s tors ,
con tr o l s
the
inpu t
s en s i t ivity o f
the
ins trumen t .
Specia l
precautions
have b e en ta ken t o
keep
any
t
h
e
rma
l
emf ' s
genera t ed t o a
minimum.
b .
The
f e edb a ck
n
e t
w
o
r
k
is
c
o
n
n
e
c
t
e
d b e tween the ou t pu t
of
tub e
V I0 3B
a
n
d
the
photo
modula tor ,
EI0 2A .
S e t t ing
the
RANGE Swi tch ,
S l ,
s e l ec t s
the
f
e
e
d
b
a
c
k res i s t o r ,
R1 3 1 ,
R1 58
and
R1 64
t o
R1 7 3 ,
u s e d
for
the
part i cu la r
rang e .
4- 6 .
AMMETER OPERATION .
When
the
FUNCTION
Swi t ch i s s e t
t o
AMPS , one
o f
res i s tors Rl 38
to
R144
is c onne c t e d
a
c
r
o
s
s
the inpu t .
The
par t i cu l ar res i s tor d
e
p
e
n
d
s upon
the
range
b e ing
us ed .
The
vo l t ag e drop a
cr
o
s
s
the
res
i
s
t
o
r
,
which
v
a
ri
e
s
f rom
10 microvo l t s
t o
100
mi l l ivo l t s ,
is then
measured
by
the Mod e l
1 5 3 ,
and read d i rect ly in ampere s .
4 - 7 . MULTIV IBRATOR. The
mu l t i
vibra t or
is
a twin- t r iod e
tub e , V 20 1 ",
whi c h
u s e s
h igh ly
s t ab l e r
e s
i
s
t
o
r
s
and
c ap a c i t o rs
in
the
f requency
d e termining
c i r cui t s .
Pot en t i ome t e r
R2 10
a d jus t s
the mu l t i
v
i
b
r
a
to
r
frequency t o e xa c t ly tha t o f
the
frequency s
e
l
e
c
t
i
v
e
amp l i
f i e r .
The
mu l t ivib ra tor
i s
u s ed t o
d rive
t h e neon
l amps
in
the
phot o-modu lat ors
•
•
14
Содержание 153
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