Tektronix 7A16A Instruction Manual page 14

Ci rcuit Descri
p
tion-7Α 16 Α
wh en
t
h e POLARITY switch is in the INVER T
p
osition . resistor
R
622. When the -15 volt time-slot
p
ulse is ap
p
lied
T
his results in the sym bol j (inverted)
b
eing displayed
to Interface Co n nector Β 33, Q620 is interrogate
d
an d its
prece
d
ing the
d
eflection factor rea
d
out .
collector current is ad d e d to t he col umn current outpu t
th ro ugh Interface Connector Α37 .
Switching resistors are
u
se d to in d icate the setting of the
VO LTS/DIV switch to the mainframe rea
d
out system . The
dots on the co ntact-closu re ch art (see Diagram Sectio n) W
it h α 1 Χ probe (or no
p
robe) connecte
d
to the I NPUT
indicate wh en the associated contacts on the VO LTS/DI V
co nn ecto r, 0620 is turne
d
off. The
d
eflection factor
cam switc h are close
d
. R
633,
R
634, and
R
635 select t he readout is determined
b
y the VO LTS/DI V switch position.
number 1, 2, or 5 d epen d ing on t he com b i nation t h at is
W
ith α 10 Χ
p
robe connecte
d
, the bias on Q620 allows 100
switched in .
R
637 selects the m (milli-) prefix an d R639 microamperes of collector current to flow . This increases
selects t he symbol V (volts) in th e 5 m V
t
hroug h .5 V
t
he
d
eflectio n factor readout by α factor of 10 .
(500 mV ) positions of th e VO LTS/DI V switc h .
R
638
selects the sym bol V in
t
h e 1, 2, an d 5 V positions.
R
630,
R
631, and th e o u tpu t of t he
p
ro b e sensing stage (Q620) The ID EN TI F Y b utton (S45 on Diagra m 1) d oes two
select th e d ecimal
p
oint (n umber of zeroes), agai n
d
e- things when
p
resse
d
:
p
en
d
ing on t he resistor combination switche
d
in by the
VO LTS/DIV switch. 1 . It causes the trace re
p
resenting the 7Α16 Α to move
(see the discussion on the
P
osition Circuit) .
P
ro be sensing stage Q620 identifies the attenuatio n
factor of the probe connected to the I NPUT co nn ector
b
y 2. Forwar d biases CR 621 and Q620 to result in α
sensing the amount of cu rrent flowing throug h
t
he
p
robe sufficie nt amount of collector current wh ich re
p
laces the
co di ng resistor locate
d
in the
p
robe connector. The output
d
eflection factor readout with
t
h e wor
d
"IDEN TI FY" .
of this circuit corrects the mainframe rea
d
out system to
incl u
d
e the
p
ro b e atte nuation factor . T h e th ird contact of
the I NPUT connector
p
rovi d es t h e i np ut to t h e
p
robe
These two actions ai
d
in identifyi ng the 7Α16 Α trace
sensing
d evice from the
p
ro be co ding resistance (co de
d
w hen multi
p
le traces are
d
is
p
layed. Wh en the ID EN TI FY
probes only ; see O
p
erating Instructions) . The th ir
d
contact
b
utton is released, the
d
eflectio n factor readout is restored.
is also use
d
for the ID EN TI F Y input. Th e co
d
ing resistor
forms α voltage divi der with R621 through CR 621 to the
-15 V
s
upply . The resultant voltage sets the
b
ias on Q620
For fu rther infor m ation on t h e operation of the readout
an
d d
etermines the collector current, along with emitter
system, see the oscillosco p e instruction manu al .