Probe Operation - Tektronix 7a11 Instruction Manual

5. Switch the oscilloscope Cali brator to 4 V an d note
that the upper excu rsions of the squ are wave are no longer
visible. If it is
d
esi re
d
to
d
isplay the uppe r po rtions of the
square wave, pull out on the oscillosco pe BEAM
F
INDER
knob, causing the enti re
d
isplay to appear on the CRT.
6. De p ress th e O FF S ET ON bu tton an
d a
dj ust th e O FF-
SET control as
n
ecessa ry to place th e top of th e sq uare
waves at graticule center .
7. Return the BEAM
F
IND ER to
n
ormal
b
y de pressing
an d releasi ng the button.
N
ote that the
u
pper portio n of
the s
q
uare wave now app ears near graticule center . Refine
the OFF SET adjustment (if
n
ecessary) to alig n
t
he to
p
s of
the square waves with the graticule ve rtical center .
8. Calculate the OFF SET voltage
b
ei ng applied. It is
equal to the OFF SET
d
ecimal value (in
d
icate
d
by the OFF-
SET
k nob) multiplied by the O FF S ET RA NGE (indicated
by the
V OLTS/DI V switc h) . In this case, the calculatio n is
-.2 Χ 20 V = -4
V . (-4
volts is
n
eede d
to retu rn α +4 V
signal to graticule center .)
9.
U
si ng α DC voltmeter and the Cable Assembly, chec k
t
he voltage available at the OFF SET OUT
j
ac k. It is equal
to the value indicated by the O FF SET knob, and can never
exceed ap
p
roximately ±1
V. N
ote that only 0.2 V is present
there, even though the offset voltage
b
ei ng applie
d
to offset
the incoming signal is equivale nt to 4
V .
10 . Turn the O FF SET
b
utton OFF an
d
disconnect the
coaxial ca ble from the oscilloscope and the STORE D
PR O BE
I
NPUT Adapter.
P
robe O
p
eration
1 . Pull out on the 7 A 1 1
L
oc king
L
atch and remove the
7 A 1 1 from the oscilloscope
p
lug-in un it compartment.
2.
L
ay the 7 A 1 1 on its left si
d
e and remove the
P
robe as
explained
i
n
t
he begi nn ing of th is sectio n . Replace the
7Α 11 in the oscilloscope
p
lug-in compartment. Allow
approxi mately 1 mi nu te to elapse b
efore continuing with
t
h e p
rocedu re .
3. De press the ID EN TI FY
b
utton near the
r
ea r of the
P
robe
b
ody and note that the trace moves approximately
1/4
d
ivision
j
ust as it
d
i
d
when the front panel ID EN TI FY
bu tton was
d
epresse
d
. If th e oscilloscope is equi p
p
e d with
readout circuitry, also
n
otice that the word "ID EN TI FY"
appears in the 7 A 1 1 readout area of the C R T.
4. Switch the oscillosco pe Calibrator to 0.4
V.
Now
touch the Pr obe tip to the Cali brator output
j
ack center
terminal and note that approximately 4 divisions of s
q
ua re
wave appears on the upper
h
alf of the CRT.
Operating Instructions-7A11
5. Disconnect the
P
ro be from the
j
ac k. Attach the AC
Coupler accessory to the Pr obe ti p. Connect the Co up ler tip
to the Cali brator
j
ac k and
n
ote that the 4
d
ivision square-
wave
d
isplay now stra ddles the ve rtical ce nte r of the grati-
cule, si nce the capacitor i n the AC Coupler
b
locks the DC
component.
6. It is suggeste
d
t
h at the
P
ro be's ot her accessories
b
e
experimented with at th is time for familiarization pu rposes .
N
ote that when the Retracta ble
H
ook Ti p is installe
d
on
either the
P
robe or the AC Coupler ti p, the
h
oo k can
b
e
ex
p
osed by pulling
b
ac k on the
r
etracting tab. Also
n
ote
that either the 3-inch or 12-i nch screw-i n grounding lead
can
b
e used with the AC Coupler ti p. An alligator clip
s
hould be attached to the opp osite end of the grou ndi ng
lea
d
s for attach ing to convenient grou nde
d
su rfaces.
7. Remove the 7Α11 from th e plug-in compartment.
Depress the tab on the si
d
e of th e STORE D PR O BE
I
NPUT
Adapter an
d
remove the Adapte r
t
h rough the front of the
7A1 1 . Retract the cable into the 7 A 1 1 a nd wind it on the
cable spool as necessary to draw the Probe th roug h the
7Α11 front
p
anel . Snap
t
he STO RE D PR O B E I NPUT
Adapter into place an d inse rt the
P
robe into the back of th e
Adapter. The 7Α11 is agai n ready fo r use i n t he sto re
d
p
robe mo
d
e.
U
nscale
d
Deflection
F
actors
On occasion , it may
b
e conven ie nt to esta blish ve rtical
d
eflection factors other than those wh ich are provi
d
ed
b
y
specific positions of the
V
OLTS/DI V switch .
F
or exam ple,
assume that 0 .8 volts/d ivisio n
d
eflection factor is desired. If
α 4-volt sq uare wave cali brator sign al is applie d to α vertical
un it
h
aving 0 .8 volts
d
eflection factor, t h e displaye d sign al
amplitu
d
e is e
q
ual to the applie
d
sign al (4 volts) d ivid e d by
the
d
eflection factor, (0 .8 volts) wh ic h is equal to 5 divi-
sions of
d
is play.
W
it h this in mi nd , set the
V
OLTS/DI V to
th e
n
ext lowe r deflectio n factor (i n th is case, .5 volts) and
apply α 4-volt signal from th e oscillosco
p
e Cali brator to th e
7Α11 Prob e inp ut . Th e n d epress and release the V AR I-
A BLE kno b
a
nd a dju st it as
n
ecessary to o b tain 5 d
ivisions
of deflection . Α 0.8 volt/division deflection facto r now is in
effect .
It shoul
d
b
e
n
oted that t h e same
r
atio of actual
d
eflec-
tion factor to
V
O LTS/DI V switch value exists in all other
switch positions. Thu s if the
V
A R IA BLE control is in the
p
osition established in the
p
rece d ing p
aragraph
a
nd the
V
OLTS/DI V switch is placed in
t
he 2
V
OLTS/DI V posi-
tion , α 3.2 volts/division d
eflection factor will b
e in effect
(0 .8 is to 0.5 as 3.2 is to 2) .
2-7