Tektronix 7a11 User manual

INSTRUCTION
MANUAL
Serial Number ?(a727
Tektronix, Inc.
S.W. Millikan Way P. 0. Box 500 Beaverton, Oregon 97005 Phone [phone] Cables: Tektronix
070-0984-00 1269

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TABLE OF CONTENTS
SECTION 1 SPECIFICATION
Introduction
Electrical
Deflection Factor
Gain
Frequency Response
Maximum lnputVoltage
lnput Rand C
Maximum Gate Current
Noise
DC Drift
DriftWith AmbientTemperature
Trace IDENTIFY
OFFSET Range
OFFSET OUT
50 SZ TerminationIAdapter
Environmental
Probe
Temperature
Altitude
Vibration
Shock
Plug-In
Altitude
Physical
Finish
Dimension
Weight
SECTION
2 OPERATING INSTRUCTIONS
General
Plug-InInsertion/Removal
Probe RemovalIStorage
External Controlsand Connectors
Accessories Information
First Time Operation
STEP ATTEN BAL Adjustment
IDENTIFY
BANDWIDTH
GAIN
POLARITY
OFFSET
Probe Operation
UnscaledDeflectionFactors
lnputCapacitance

TABLE OF CONTENTS (cont)
SECTION 3 CIRCUIT DESCRIPTION
Block Diagram Description
Probe Circuit Description
Input Amplifier
Output Amplifier
Offset Generator
VoltsIDiv Switch and Readout
Power Supplies and Output Connectors
SECTION
4 MAINTENANCE
PreventiveMaintenance
General lnformation
Cleaning
Visual Inspection
Lubrication
Transistor and IntegratedCircuit Checks
Recalibration
Troubleshooting
Test Equipment
General Techniques
TroubleshootingBasic Components
TroubleshootingChart
Corrective Maintenance
Parts Procurement
Screwdriver Requirements
Soldering Equipmentand Techniques
Probe Data
Plug-InUnit Data
Circuit Board Illustrations
SECTION
5 PERFORMANCECHECKICALIBRATION
General
CalibrationProcedure lnstructions
PerformanceCheck lnstructions
CalibrationIndex and Record lnstructions
Equipment Required
DetailedProcedure
SECTION
6 ELECTRICALPARTS LIST
Abbreviations and Symbols
PartsOrdering Information

TABLE OF CONTENTS (cont)
SECTION 7 DIAGRAMS
Electrical
MechanicalParts List Illustrations
Accessories
SECTION
8 MECHANICALPARTS LIST
MechanicalParts List Information
CHANGE INFORMATION
Abbreviations and symbols used inthis manual are
based on or taken directly from IEEE Standard
260 "Standard Symbols for Units", MIL-STD-12B
and other standards of the electronics industry.
Change information, ifany,
is located at the rear of
this manual.
iii

Fig. 1-1. 7A11 Amplifier.
8

SECTION 1
Introduction
Changeinformation, ifany, affecting thissectionwillbe found at therear of rhe manual.
The 7A11 Amplifier is a versatile plug-inamplifier unit
which provides a DC to 150 MHz bandwidth with Tek-
tronix 7700-Series Oscilloscopes. When desired, the upper
frequency -3 dB point can be limited to 20 MHz by a
front-panelswitch.
Calibrated deflection factors of from 5 mV to 20 V per
division are provided in 1-2-5sequence. In addition, avari-
able gain control makes
it possible to set the amplifier to
any deflection factor between 5 mV and 50V per division.
A permanently attached probe provides low-inputcapa-
citance (2.0 pF at 2 Vldivision, 5.8 pF at 5 mVldivision)
while maintaining high input resistance (1 Ma). BNC-
connectors can be attached to the probe through a probe-
tip to BNC-female adapter. This adapter serves as the
probe's input connector when the probe is stored, but can
be attached to the probe tip whether or not the probe
is
stored intheplug-inunit.
A 50 terminationladapter (standard accessory) per-
mits impedance matching for use of the probe in 50
environments. When the terminationladapter is used, alow
standing wave ratio (VSWR) can be expected. The VSWR
can be further reduced by insertinga 2X attenuator inthe
signal path ahead of the 50
St terminationladapter. Approx-
imate values of VSWR which can be expected under both
conditionsare shown in Fig. 1-4.
The performancespecification of the 7A11 Amplifier is
described in detail in Table 1-1. The specification is valid
under thefollowing conditions:
Calibrationmust have been performed at an ambient
temperaturebetween +20°c and +30°c.
TABLE 1-1
7Al I Amplifier Specification
Characteristic
ELECTRICAL
Gain Ratio
Accuracy
Uncalibrated
PerformanceRequirement
DeflectionFactor
(VO
LTSID I V)
Calibrated Range
Within 2% of GAIN adjusted at 0.1
Vldiv
5 mVldiv to 20 Vldiv; 12 steps in
5,10,20 sequence
Continuously variable; extends de-
flection factor to at least 50 Vldiv
Permits adjustment of deflection
factor at 0.1 Vldiv for all Oscillo-
scopes
Frequency Response
(8Division Reference)
Bandwidth, Direct
Coupled Input
DC to 90 MHz with 7500-Series
Oscilloscope
FULLMode DC to 150 MHz with 7700-Series
Oscilloscope
20 MHz Mode
Risetime
1 2.4 ns or less with 7700-Series
DC to 20 MHzwithin
2 MHz
Capacitive Coupled
Lower Frequency
-3 dB Limit
1 oscilloscope
15 Hz or less
1 3.9 ns or less with 7500-Series
Operation must be within any specifiedenvironment,
in
a calibrated Oscilloscope, after twenty minutes of
warmup.
REV. MAR 1974
Risetime (6 Div
Reference)
Oscilloscope
12011s or less 5 mV-20Vldiv with
7904 oscilloscope.

Specification-7Al1
TABLE 1-1 (cont)
TABLE 1-1(cont)
Maximum lnputVolt-
age With or Without
AC Coupler Installed
Characteristic
DC
+ Peak AC
Performance Requirement
200 V; AC component not to ex-
ceed amplitude specified under AC
AC, continuous
wave
5 mV thru
50 mV
0.1 V thru
1 v
2 V thru
20 v
200 V peak to 50 kHz; see Fig. 1-2
for amplitude derating due to fre-
quencies above
50 kHz
200 V peak to 40 MHz; see Fig. 1-2
for amplitude derating due to fre-
quencies above
40 MHz
200 V peak to 70 MHz; see Fig. 1-2
for amplitude derating due to fre-
quencies above
70 MHz
DC, Capacitive
Coupled (AC
Coupler Installed)
lnput Rand C
Resistance
1 M!2 within 1%
Capacitance
5 mVldivthru
50 mVldiv Approximately
5.8 pF
0.1 Vldiv thru
1 Vldiv Approximately
3.4 pF
2 Vldiv thru
20 Vldiv
MaximumGate
Current
Noise (Tangentially
measured in FULL
Mode)
Approximately
2.0 pF
0.25 nA or less at 25"~,increasing
to
1.2 nA or less at 50"~
0.1 division (maximum), measured
in7000-SeriesOscilloscope
Characteristic
DC Drift
DriftWith Time
(Ambient Temper-
atureand Line Vol-
tage Constant)
Short Term
LongTerm
DriftWith Ambient
Temperaturechange
(LineVoltageConstant)
Plug-InOnly
Probe Only
Trace IDENTIFY
OFFSET Range
5 mV1div thru
50 mVldiv
0.1 Vldiv thru
1 Vldiv
2 Vldiv thru
20 Vldiv
OFFSET OUT
Range
Ratio of Offset
Range toOFFSET
OUT
5 mV1divthru
50 mVldiv
0.1 Vldiv thru
1 Vldiv
2 Vldiv thru
20 Vldiv
Source Resistance
Performance Requirement
0.1 division or less during any 1
minute interval within 1 hour after
20 minutesfrom turn-on
0.3 division or less duringany hour
after
20 minutesfrom turn-on
200 ~v/"c or less
200 ~v/"c or less
0.2 to 0.3 division upward trace
shift
+I V to -1 V
+20 V to -20 V
+400 V to -400 V
+I V to -1 V (nominal)
1 : 1 within 1% plus 0.5 mV at OFF-
SET OUT jack
20: 1 within 1.5% plus 0.5 mV at
OFFSETOUT jack
400: 1 within
2% plus 0.5 mV at
OFFSET OUT jack
500 i-2 within 3%

Fig. 1-2. Frequency versus maximum input amplitude derating graph.
TABLE 1-1 (cont)
1000 v
200 v
100 v
Peak
Voltage
10 v
Characteristic
50 52 Termination1
Adapter
Input Impedance
1 v
--
PerformanceRequirement
I
50 52 within 1%
10 kHz 100 kHz 100 MHz I GHz
MHz CW Frequency lo MHz
Power Rating
ENVIRONMENTAL
1 Watt
Probe
Temperature
Non-operating
Operating
Altitude
I
Operating
Non-operating
Vibration
To
50,000 feet
To
15,000 feet
l5 minutes along each axis at 0'025
Fig. 1-3. 7All maximum gate current versus Probe ambient tem-
inch p-p displacement (3.9 g's at
perature in "non-stored" mode. To determine maximum gate cur-
55 c/s) 10 to 55 to 10 c/s in rent with Probe stored, add +ll°C to Probe ambient temperature.

1.4
VSW R
1.3
1
.o
1 MHz 10 MHz 100 MHz
FREQUENCY
1 GHz
ArtekMedia
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Date: 2008.11.16 13:33:28 -06'00'

TABLE 1-1 (cont)
h he Plug-In environment is dependent upon the oscilloscope. See
the environmental specification in the applicable oscilloscope
manual.
Characteristic
Shock
Plug-ln'
Altitude
Non-operating
PHYSICAL
Finish
Plug-In
Specification-7Al1
TABLE 1-1(cont)
PerformanceRequirement
1-minute cycles. Three minutes
at
any resonant point or, if none, at
55
CIS
400 g's, 112 sine; 3 shocks along
each axis
at 112 ms, 1 ms and 2 ms
duration (totalof 27 shocks)
To 50,000 feet and
-55'~
Anodized aluminum front panel
Characteristic
Probe Body
Dimensions
Plug-In
Probe Body
Probe Cable
Weight, Plug-In
and Probecom-
bined
Net
Shipping
Performance Requirement
Grey plastic housing
44.58 inches' long, 2.75 inches
wide, 4.98 incheshigh; overall
m6.53 inches long, 0.63 inches
wide, 0.66 incheshigh; overall
m8.83 feet long
m2.75 pounds
m4.5 pounds

NOTES

SECTION 2
General
OPERATlNG INSTRUCTIONS
Changeinformation, if any,affecting thissection will be found at therear of themanual.
EXTERNAL CONTROLSAND CONNECTORS
This sectioncontainsan explanationof externalcontrols
and connectors for the Plug-In Unit (Fig. 2-1) and
its
attached Probe (Fig. 2-2). It also containsan explanationof
accessories, afirst-time operating procedure and additional
operating hints.
It is recommended that this sectionbe read
in
its entirety prior to normal usage of the 7A11 Plug-In
Unit and Probe.
PLUG-IN INSERTION AND REMOVAL
The 7A11 is calibratedand ready for use as received. It
can be installed in any compartmentof 7000-Seriesoscillo-
scopes, but is intendedfor principal use in vertical plug-in
compartments. To install, alignthe upper and lower railsof
-
the 7All with the oscilloscope tracks and fully insert it.
The front will be flush with the front of the oscilloscope
when the 7A11 is fully inserted, and the latch at the
bottom-leftcorner of the 7A11 will be inplace against the
--
front panel.
To remove the 7A11, pull on the latch (which is in-
scribed with the unit identification "7A11") and the7A11
will unlatch. Continue pulling on the latch to slide the
7A11out of the oscilloscope.
PROBE REMOVAL AND STORAGE
To remove the Probe: With the 7A11 Amplifier re-
moved from the oscilloscope, locate the Probe and Stored
Probe lnput Adapter on the right side of the 7A11 (Fig.
2-2A). Move the Probe back, disconnecting it from the
Adapter. Note the plastic latch (labeledPRESS) on the side
of the Adapter housing. While holdingthis latchdepressed,
move the Adapter out through the front of the 7Al1,
as in
Fig. 2-2(B).
Uncoil the desired number of turns of cable from the
cable drum and remove the Probe through the Adapter
access hole. When the Probe and cable have been removed
far enough to take up theslack cable within the 7All.clip
the Adapter to the cable as shown in Fig. 2-2(C). Then
insert the Stored Probe lnput Adapter into its housing in
the 7A11, as in Fig. 2-2(D). Reverse the procedureto re-
installthe Probe.
Plug-In Unit
VOLTSID I V A 1 2-position switch graduated
from
5 mV through 20 V in
5-10-20sequence. Inaddition tose-
lectingcalibrateddeflectionfactors,
it indicates the input capacitance
and offset voltage range applicable
toeach switch position.
VARIABLE Combination switch and potentio-
(CAL IN) meter. When the control is in
its in-
ward position, deflection factors
are as indicatedby the VOLTSIDIV
switch. Push and release knob to
enable selection of uncalibratedde-
flection factors between the value
indicated by the VOLTSIDIV
switch and at least 2.5 times that
value.
POSITION Moves display vertically on CRT
when Plug-In Unit is in vertical
compartment of oscittoscope. Per-
mits horizontal movement of dis-
play when Plug-In is in horizontal
plug-in compartment of oscillo-
scope.
l DENTIFY Located in center of POSITION
knob. When pushed, causes approx-
imately 114 division movement of
display. Oscilloscopes equipped
with readout simultaneously dis-
play the word "IDENTIFY" in the
7A11 readoutarea on the CRT.
OFFSET
ON-OFF Permits or inhibits operationof the
OFFSET control.
COARSE Outer of two concentric knobs.
Stop-to-stop rotation injects offset
voltage equivalent to
+I through
-1, +20 through -20, or
+400
through -400 volts at the inputs,
depending upon position of

Operating Instructions-7Al1
COARSE VOLTSIDIV switch. Counterclock-
(cont.) wise position offsets the input with
a negative voltage, clockwise posi-
tion offsets the input with a posi-
tive voltage.
Fig. 2-1. 7All Front Panel.
FINE Inner of two concentric knobs. One
revolution injects an equivalent of
approximately 0.4, 4, or 40 volts
offset voltage, dependent upon po-
sition of VOLTSIDIV switch.
POLARITY
Selects upward deflection for
positive-going input signals. If the
7A11 is used inahorizontal plug-in
compartment, selects right deflec-
tion for positive-going signal.
INVERT
BANDWIDTH
FULL
20 MHz
STEP ATTEN BAL
OFFSET OUT
GAIN
STORED PROBE
INPUT
Release Latch
Selects downward deflection for
positive-going input signal. If the
7A11 is being used in a horizontal
plug-in compartment, selects left
deflection for positive-going input
signal. Upward (or right) deflection
for positive going input signals is
provided if both switchesare inthe
outward position.
Provides full bandwidth as specified
for 7AlI-oscilloscopecombination.
Reduces upper frequency
-3 dB
limit of 7Al
I -oscilloscope to 20
MHz. Full bandwidth is provided if
both switches are in the outward
position.
Externally balances circuitry to
avoid shifting of no-signal trace
when VOLTSIDIV switch position
is changed.
Miniature phone jack, making selec-
ted value of offset voltage available
externally. No output provided
when OFFSET switch
is OFF.
Screwdriver adjustment permitting
external calibration of VOLTS1
DIV. Normally adjusted with
VOLTSIDIV at .I position as indi-
cated by the shaded area surround-
ing the
.I at the VOLTSIDIV
switch.
BNC jack connected to Probe tip
when Probe
is stored within 7A11
Amplifier. Notethat value ofcapac-
itance indicated at VOLTSIDIV
switch must be increased by 1.2 pF
when the STORED PROBE INPUT
Adapter
is used. When Probe is
withdrawn from 7A11 Amplifier,
STORED PROBE INPUT
is usually
disconnected from the circuit. Max-
imum allowable DC plus peak AC
input voltage is 200 volts. Consult
specification section for derating
due to frequency.
Latch inscribed with plug-in identi-
fication "7All". Pull knob to re-
lease latch when removing 7A11
from oscilloscope.

Operating Instructions-7ATl
Adapter
,, , Adapter install
ring StoredProbe I npc ~t Adapter. Note that Probehas
I
-
d cable,
men diseng
i
aged from Adapter.
nded.
Fig. 2-2. Probestorage and removal.
8

Operating Instructions-7Al1
Probe
Tip
Fig. 2-3. (A) Accessories; (6) Accessories installed.
IDENTIFY
pushbutton
Miniature tvpe, DC-coupled to in-
..
ternal circuitry. Can be equipped
with DC blocking capacitor (see
Accessory Information). Can also
be equipped with pincher tip or
hook tip for attaching Probetocir-
cuitry. Maximum allowable DC
+
peak AC input is 200 volts. Consult
specification section for derating Ground Contact
due tofrequency.
Depressing
it causes approximately
114 division trace shift. Also causes
the word "IDENTIFY" to appear
in 7All readout area on CRT if
oscilloscope
is equipped with read-
out circuitry.
Female-threadedcontact for attach-
inggrounding lead.

OperatingInstructions-7Al1
ACCESSORIES INFORMATION FIRST TIME OPERATION
.
-_
Accessories are supplied with the Probe to extend its
operating capabilities. These accessories are shown in Fig.
2-3 and are intendedto be utilized as follows:
1. AC Coupler. Slip-ontypecontaininga .015 pFcapac-
itor. Blocks DC from Probe. Has a 15 Hz low-frequency
-3
dB point. Adds 2.4 pF to input capacitance indicated at
VOLTSIDIV switch.
2. Retractable Hook Tip. Slip-on type for use with or
without AC Coupler. Adds additional 1 pF input capaci-
tance. Hook Tip body moves toward rear of Probe to ex-
pose hook. Contains female-threaded ground connection
for use with either a
3 inch or 12 inchscrew-inground lead.
3. Hook Tip. Slip-ondevice for use with or without AC
Coupler.
4. Insulating Tube. Slip-ondevice for insulating ground
surface at Probetip or AC Coupler tip.
5. Bayonet Ground. Slip-ondevice for use with or with-
out AC Coupler. Spring loaded contact permitscompleting
the Probe ground circuit immediately adjacent to Probe
signal inputtip.
L
6. Grounding Lead, Nose. Slip-on device which makes
contact with ground surface
at Probe or AC Coupler tip.
Other end equipped with
6-32 male thread for attachment
toalligator clip.
7. Grounding Lead, Screw-In,
3 inch. Primarily for use
with Retractable Hook Tip. Threaded both ends. One end
to be attached to Retractable Hook Tip, other end for use
with alligatorclip.
8. Grounding Lead, Screw-In, 12 inch. Threaded both
ends. For use between threaded female groundingcontact
at Probe and alligator clip. Can also be attached between
grounding female thread at Retractable Hook Tip and alli-
gator clip.
9. Alligator Clips. For use with grounding leads.
10. 50
52 TerminationIAdapter, GR-to-probe tip. Can
be used in any situationrequiring50
S2 probe input imped-
ance.
L 11. Cable Assembly. Equipped with miniature
telephone-jack plug, coaxial cable, and alligator clips. For
use with OFFSET OUTjack.
General
Operation of the 7A11 Amplifier and Probe inavertical
plug-in compartment of an oscilloscope is explained here.
Operation of the unit with the Probe stored
is explained
first. This isfollowed by adescriptionof operationwith the
Probeand itsaccessories.
Preliminary
Install the 7A11 Amplifier into a vertical compartment
of a 7000-Series oscilloscope equipped with a time-base
unit. Set the equipment controlsas listed inTable 2-1.
TABLE 2-1
PreliminaryControlSettings
7AllAmplifier
VOLTSID I V .1
POSITION Midrange
OFFSET OFF
POLARITY +UP
BANDWIDTH FULL
Time
Base
Triggering
Mode
Coupling
Source
Magnifier
TimeIDiv
Variable
Auto
AC
Int
XI
1mS
Calibrated
Oscilloscope
Intensityand Focus Adjusted for OptimumTrace
Beam Finder Normal
Calibrator
.4 V
Rate 1kHz
STEP ATTEN BAL Adjustment
1. Using the 7A11 POSITION control, set the trace to
vertical center of the graticule. Then depress the INVERT
button and notethe trace position.
2. Using the STEP ATTEN BALcontrol, movethetrace
to a point midway between its present position and the
verticalcenter of the graticule.
3. Again using the POSITION control, set the trace to
graticule center. Then depress the +UP button and again
note the trace position.
It shouldhave remainedat graticule
center. If not, again adjust STEP ATTEN BAL to position
the trace midwaybetween itspresentpositionand graticule
verticalcenter.

OperatingInstructions-7Al I
4. Repeat this procedure until no trace shift accompa-
nies switchingbetween+UP and INVERT.
5. Check STEP ATTEN BALadjustment by rotatingthe
VOLTSIDIV switch through all positions and noting that
notrace shift occurs.
6. The STEP ATTEN BAL adjustment should be re-
checked each time the 7A11
is used. Do not use theSTEP
ATTEN BAL adjustment as apositioncontrol.
IDENTIFY
1. Depress the 7A11 IDENTIFY button while observing
the trace. Note that the trace shifts upwardapproximately
114 division when the button is pushed, and returns to its
previouspositionwhen the button is released.
2. If the oscilloscope isequippedwith readoutcircuitry,
note that the word "IDENTIFY" appears inthe 7A11 read-
out area of the CRT while the IDENTIFY button
is pushed.
The deflection factor in use should appear in the readout
area when the IDENTIFY button is released.
BANDWIDTH
1. Adjust the oscilloscope Intensity and Focus controls
to obtain optimumtrace sharpness.
2. Depress the FULL Bandwidth switch and note that
the trace becomes slightly less clearly defined. This occurs
because
a much wider frequency range is now being dis-
played,and the total noise increases accordingly.
A better indication of bandwidth operation can be ob-
tained by connectingthe output from ahigh-frequencygen-
erator to the STORED PROBE INPUT. With 20 MHz
applied from the signal generator, and FULL selected
at
7A11, adjust for 5 divisions of vertical display. Then select
20 MHz
at the 7A11 and note that the vertical amplitude
decreases to approximately3.5 divisions.
GAlN
1. Connect a 50 C? coaxial cable between the STORED
PROBE INPUT and the Calibrator output jack
at the
oscilloscope.
2. Note that with 0.4 V and 1 kHz selected
at theCali-
brator and
.I VOLTSIDIV selected at the 7A11, a display
of approximately4divisions appears on the CRT.
Adjusting the GAlN control with the oscilloscope Cali-
brator signal applied provides absolute accuracy to within
2% in the adjusted position at temperatures between
OOC
and 50'~.Other deflection factors will then be accurate to
within
4% absolute between O'C and 50'~.
If greater gain accuracy is required, a more accurate
amplitude calibrator must be used and
all instrumentsmust
be restricted to
a temperature range of 15'~to 35'~.The
Tektronix Amplitude Calibrator and Comparator, Part No.
067-0502-01
is recommended for this purpose.An absolute
accuracy approaching 2% may then be obtained over the
rangeof deflectionfactors.
POLARITY
1. Disconnect the coaxial cable from the STORED
PROBE INPUT Adapter. Then adjust the 7A11 POSI-
TION control
as necessary to place the trace at graticule
verticalcenter.
2. Reconnectthe coaxial cable to the STORED PROBE
INPUT Adapter and note that the
1 kHz square wave is
displayed in a positive or upward direction from the refer-
ence positionestablished
at graticulecenter.
3. At the 7A11, depress the INVERT button. Notethat
now the positive-goingsquare wave
is deflected in adown-
ward direction on the CRT.
4. Depress the +UP button to regain upward deflection
of the positive-goingsquare wave.
OFFSET
1. Adjust the outer OFFSET knob as necessary to place
itswhite marker
at 0.
2. Depress the OFFSET ON button. The trace may shift
upwardor downward.
3. Move the OFFSET controls and note trace reaction.
Clockwise movement causes upward deflection, while
counterclockwise movement causes downward deflection.
Also note that the FINE control knob causes considerably
less reaction than the COARSE control knob. (The two
knobs have
a ratio of approximately 10:1 .)
4. Depress the OFFSET OFF button. The square wave
display should now appear inthe upper half of the CRT.

Operating Instructions-7Al1
5. Switch the oscilloscope Calibrator to 4 V and note
that the upper excursions of the square wave are no longer
visible. If
it is desired to display the upper portions of the
square wave, pull out on the oscilloscope BEAM FINDER
knob, causingthe entiredisplay toappear on the CRT.
6. Depress the OFFSET ON button and adjust the OFF-
SET control
as necessary to place the top of the square
waves
at graticule center.
7. Return the BEAM FINDER to normal by depressing
and releasing the button. Note that the upper portion of
the square wave now appears near graticule center. Refine
the OFFSET adjustment (if necessary) to align the tops of
the square waves with the graticuleverticalcenter.
8. Calculate the OFFSET voltage being applied.
It is
equal to theOFFSET decimal value (indicatedby the OFF-
SET knob) multiplied by the OFFSET RANGE (indicated
by the VOLTS/DIV switch). Inthis case, thecalculation
is
-.2 X 20 V = -4 V. (-4 volts is needed to return a +4 V
signal to graticulecenter.)
9. Using a DC voltmeter and the Cable Assembly, check
the voltage available
at the OFFSET OUT jack. It is equal
to the value indicated by the OFFSET knob, and can never
exceed approximately
*I V. Notethat only 0.2 V is present
there, even though the offsetvoltage beingapplied to offset
the incomingsignal
is equivalentto 4 V.
10. Turn the OFFSET button OFF and disconnect the
coaxial cable from the oscilloscope and the STORED
PROBE INPUTAdapter.
Probe Operation
1. Pull out on the 7Al I Locking Latch and remove the
7Al
I from the oscilloscope plug-inunit compartment.
2. Lay the 7A11 on
its left side and remove the Probe as
explained in the beginning of this section. Replace the
7A11 in the oscilloscope plug-in compartment. Allow
approximately 1 minute to elapse before continuing with
the procedure.
3. Depress the IDENTIFY button near the rear of the
Probe body and note that the trace moves approximately
114 division just as it did when the front panel IDENTIFY
button was depressed. If the oscilloscope
is equipped with
readout circuitry, also notice that the word "IDENTIFY"
appears inthe 7A11 readoutarea of the CRT.
4. Switch the oscilloscope Calibrator to 0.4 V. Now
touch the Probe tip to the Calibrator output jack center
terminal and note that approximately 4 divisionsof square
wave appears on the upper half of the CRT.
5. Disconnect the Probe from the jack. Attach the AC
Coupler accessory to the Probe tip. Connect the Coupler tip
to the Calibrator jack and note that the 4 division square-
wave display now straddles the vertical center of the grati-
cule, since the capacitor in the AC Coupler blocks the DC
component.
6. It is suggested that the Probe's other accessories be
experimented with at this time for familiarizationpurposes.
Note that when the Retractable Hook Tip
is installed on
either the Probe or the AC Coupler tip, the hook can be
exposed by pulling back on the retracting tab. Also note
that either the 3-inch or 12-inch screw-in grounding lead
can be used with the AC Coupler tip. An alligator clip
should be attached to the opposite end of the grounding
leads for attaching to convenientgrounded surfaces.
7. Remove the 7Al
I from the plug-in compartment.
Depress the tab on the side of the STORED PROBE INPUT
Adapter and remove the Adapter through the front of the
7A11. Retract the cable into the 7Al I and wind it on the
cable spool as necessary to draw the Probe through the
7A11 front panel. Snap the STORED PROBE INPUT
Adapter intoplace and insert the Probe intothe back of the
Adapter. The 7A11
is again ready for use in the stored
probemode.
Unscaled Deflection Factors
On occasion, it may be convenient to establish vertical
deflection factors other than those which are provided by
specific positions of the VOLTSIDIV switch. Forexample,
assume that 0.8 voltsldivisiondeflectionfactor
is desired. If
a 4-volt square wave calibrator signal is appliedto a vertical
unit having 0.8 volts deflection factor, the displayed signal
amplitude
is equal to the applied signal (4volts) divided by
the deflection factor, (0.8 volts) which
is equal to 5 divi-
sions of display. With this in mind, set the VOLTSIDIV to
the next lower deflection factor (in this case,
.5 volts) and
apply a 4-volt signal from the oscilloscopeCalibratorto the
7Al
I Probe input. Then depress and release the VARI-
ABLE knob and adjust
it as necessary to obtain 5 divisions
of deflection. A 0.8 volt/division deflectionfactor now
is in
effect.
It should be noted that the same ratio of actual deflec-
tion factor to VOLTSIDIV switch value exists in all other
switch positions. Thus if the VARIABLE control
is in the
position established in the preceding paragraph and the
VOLTSIDIV switch is placed in the 2 VOLTSIDIV posi-
tion, a 3.2 voltsldivisiondeflection factor will be in effect
(0.8
is to 0.5 as 3.2 is to 2).