Tektronix 576 - Page 58

VEB ( B AS E GR O UN D ED) .
By use of α variable voltage
d ivider across t h ese
terminals, t he d eflection factor of t he
horizontal d is p lay
can be varie d .
V oltage Sensing Lea k age M od e . Wh e
n
t
he Mo de switc h
is set to LE A K AG E, only t h e measurement
of
V ςΕ
an d
V ςΒ are useful . In t h is situation α slig h
t
error
in voltage
measurement occ u rs w h enever t h e
VER TICA L switc h is set
wit h in t h e 500 ηΑ to 1 ηΑ EM ITT ER
range
. In
t h is range
(see Fig . 3-10) t h e horizontal d is p lay is α measurement of
collector voltage to groun d , rat h er t han collector to emitter
or collector to base voltage . As d iscusse d p reviously, w h en
curre n t measurements are made i n t he lea k age mode, t he
current sensing resistor is between groun d an d t he emitter
or ground an d t he base terminal . Any measurement of
volt-
age between t h e collector an d ground ,
t
h erefore, measures
t h e voltage d ro p across t h e current sensi n g resistor an d add s
it to t he desire d
measurement
of
V ςΕ or V ςΒ . T he correct
values of V ςΕ or V ςΒ can be determined by s ub t r acting
t
he voltage drop across t he curre n t sensing resistor from t he
total measurement s h ow n on t he h orizontal axis of t he
C R
T . See t he H orizontal Measurement an d Sensitivity sec-
tion
of t he Operating Instructions for i n structions on h ow
to determi ne t h is error voltage .
Dis p lay of
Ste
p
Generator . If eit h er t he VER TICA L or
t he HO
R IZO N TA L switc h is set to ST EP G EN, t he 1/2 volt
ste p
s at t
he
in
p
u
t
to t
he
outp ut
am p lifier section of t he
step am p lifier (see Fig . 3-7) are ap plie d to t h e in p uts to t h e
vertical d is p lay
amplifier
or
t he h orizontal dis p lay am p lifier
(see Fig .
3-11) . If both switc h es are set to ST EP G EN, t he
1/2 volt ste p s are a pp lie d to t he H orizontal Dis p lay Am p li-
fier only .
V ertical an d H orizontal P ositioning
The p ositioning of t he dis p lay on t
h
e C
R T is determi ned
by current app lie d to t he low imped
ance
i
n p uts
of
t h
e Dis-
play Am p lifiers at t he emitters of Q533A an
d Β i n t he
vertical dis p lay am p lifier, and 0633 Α and Β in t he
h orizon-
tal dis p lay am p lifier (see disc u ssion of Dis p lay Am
p
lifiers)
.
T h is current comes from many in d ividual current sources
w h ic h are controlle d b y t h e P OSITIO N switc h es, t he FI NE
P OSITIO N controls, t he P O L A R ITY switc h and t he DIS-
PL AY O FF S E T controls (see t
h
e Dis p lay P
ositioning
sc h ematic) .
T he P OSITIO N switc h es an d t he FI NE P OSITIO N con-
trols allow
both coarse an d fi ne p ositioning of t he dis p lay .
T
h
e
cu rrent for the coarse control comes from resistors
R 480 t h roug h R 483 (vertical) and R 490 t h ro ugh 8493
( h orizontal) . T h ese resistors are all connecte d to t he -75
volt su pp
ly, ma k ing t h em current sources . E ac h of t h ese
current sources
is connected between α p air of con tacts .
Wh en one contact of α p air is
close d , t h is current flows i n to
one si deof t he dis
p
lay
am p lifier . If t he ot h er contact of t he
pair is closed, t
h
e current flows
into the ot h er si de of the
am p lifier . T he matrixes for
t
he P OSITIO N
cam switc h
es
sh ow t h at at all
times
one
contact of each p air m u st be
close d , but
never bot h close d at once . T h is assures t h at t he
sum of t he p ositioning curre n t flowing into t h e amplifiers is
Ci r
cuit Description-Type 576
VER TICA L
N ote :
If H orizo n tal is set to
ST EP G EN, 1/2 volt
ste p s a r e not available
to V ertical Dis p lay Am -
p lifie r .
To Ho r izo n tal
Display Switc h ing
F ig . 3-11 . S i m p l
ified
sc
h
ematic
o f D is pl ay Sensitivity Sw i tc h ing
w h en V ERTI C AL and/or
H
OR IZ O
NT A L switc h es are set to S TEP
G EN .
always α consta n t . E ac h
P
OSITIO N switc h provi d es 20 divi-
sio n s of positio n ing in five d ivisio
n
ste p s . T he FI NE POSI-
TION controls, R 488 (vertical) an d 8498 ( h orizontal) op er-
ate in α similar
manner
to
t h
e
coarse con trols exce p t t h at
t he a d j ustme n t is continuo u sly variable .
T h e P O L A R ITY switc h provi d es auto m atic p ositioning
of t he d is p lay w h en switc h ing between t he AC, +( ΝΡΝ ) or
-( ΡΝΡ ) p ositions of t he switc h . T h is positio n ing current is
obtaine d in t he same manner as t he coarse p ositioning cur-
rent . Current sources R 474 and R 475 (vertical) and R 477
a nd R 478 ( h orizo n tal) p rovi de t h is p ositioning curre n t .
T he d is p lay may also be p ositione d by t he cali b
rate d
C EN T ERL I NE
V
A
LUE switc h . T h is control effects t he cir-
cuit only w
h
en
t he DIS PL AY O FF S E T Selector switc h is
switc hed to one of its VER T or H O R IZ p
ositions and
affects only one dis p
lay am p lifie r at α time . Wh en t h e DIS-
PL AY O FF SE T Selector switc h is set to N O RM (O FF
),
cur
r e
n t sources R 468 and R 469 (vertical) and R 471 an d
R 472 ( h orizontal) su pp ly cu rrent to t h e d is p lay am p lifiers .
Wh en, for exam p le, t he switc h is set to VER T, R 468 and
8469 are d isconnecte d from t he circuit and an e q ual
amount of current is su pp lie d to t he vertical display
am p li-
fier by current sou r ces R 450 t h roug h R
464 .
T
h
ese
resistor-
contact combination s a r e co n t r olle d by t he C EN T ERL
I NE
VA LUE switc h and o p e r ate
i den tical to t he P OSITIO N
switc h es . T
h
e C
EN T ERL I NE VA LUE switc h p rovides 10
d ivisions of
calibrate dp ositio n i ng in h alf- d ivision steps .
3-
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