Tektronix 7812 User manual

Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon
070-1244-00
Product Group 42
97077
Tektrone<
COMMITTED TO EXCELLENCE
PLEASE CHECK FOR CHANGE INFORMATION
AT THE REAR OF THIS MANUAL.
7812
TDR/SAMPLER
S/N B020000-up
INSTRUCTION MANUAL
Serial Number
First Printing NOV 1971
Revised JUN 1986

Copyright © 1971 Tektronix, Inc. All rights reserved.
Contents of this publication may not be reproduced in any
form without the written permission of Tektronix, Inc.
Products of Tektronix, Inc. and its subsidiaries are covered
by U.S. and foreign patents and/or pending patents.
TEKTRONIX, TEK, SCOPE-MOBILE, and are
registered trademarks of Tektronix, Inc. TELEQUIPMENT
is a registered trademark of Tektronix U.K. Limited.
Printed in U.S.A. Specification and price change privileges
are reserved.
INSTRUMENT SERIAL NUMBERS
Each instrument has a serial number on a pariel insert, tag,
or stamped on the chassis. The first number or letter
designates the country of manufacture. The last five digits
of the serial number are assigned sequentially and are
unique to each instrument. Those manufactured in the
United States have six unique digits. The country of
manufacture is identified as follows:
Bo00000 Tektronix, Inc., Beaverton, Oregon, USA
100000 Tektronix Guernsey, Ltd., Channel Islands
200000 Tektronix United Kingdom, Ltd., London
300000 Sony/Tektronix, Japan
700000 Tektronix Holland, NV, Heerenveen,
The Netherlands

SECTION 1
SECTION 2
SECTION 3
SECTION 4
7812
TABLE OF CONTENTS
CHARACTERISTICS
Description
Electrical Characteristics
Physical Characteristics
Environmental Characteristics
OPERATING INSTRUCTIONS
General Information
Installation
Controls and Connectors
First Time Operation
Voltage Reflection Coefficient
Impedance Scale Overlays
Time or Distance Measurements
High Resolution
Single Sweep Operation
PRESET Calibration
Application Connections
Using TDR Slide Rule
CIRCUIT DESCRIPTION
Introduction
Vertical Circuits Block Diagram
Horizontal Circuits Block Diagram
Circuit Description
MAINTENANCE
Introduction
Lubrication
Troubleshooting
Tape Dial Removal
Tape Dial Installation
Tape Dial Alignment
Revised NOV 1984
Page
1-1
1-1
1-5
1-5
2-1
2-1
2-1
2-5
2-8
2-8
2-11
2-11
2-12
2-12
2-14
3-1
3-1
3-4
3-10
4-4
4-4
4-1
4-2
4-2
4-2
SECTION 4 MAINTENANCE (cont)
SECTION 5
SECTION 6
SECTION 7
SECTION 8
Page
Readout Symbol Adjustment
} and XJ 4-2
Repackaging for Shipment 4-3
PERFORMANCE
CHECK/ADJUSTMENT
Introduction 5-1
Equipment Required 5-1
Performance Check and Adjustment
Record and Index 5-2
7812 Checks 5-3
S-6, S-52 and 7S12 System Checks 5-5
S-5, S-54 and 7S12 System Checks 5-7
Adjustment Procedure 5-9
ELECTRICAL PARTS LIST
DIAGRAMS AND CIRCUIT BOARD
ILLUSTRATIONS
Symbols and Reference Designators
Schematic Diagrams and Component
Board Locations
MECHANICAL PARTS LIST
Mechanical Parts List
Mechanical Parts List Illustration
Accessories

7$812
—-o
S-6 SAMPLING HEAD
Fig. 1-1. 7S$12 TDR/Sampler unit.

ee,
7812
SECTION 1
CHARACTERISTICS
Description
The 7S12 is a dual-purpose plug-in unit for measurement
of recurring fast-rise signals or for time-domain
reflectometry. It occupies two compartments (one vertical
input and one horizontal input) of a Tektronix 7000-series
oscilloscope.
The 7S12 has two compartments for plug-in heads. The
left-hand compartment (labeled SAMPLING on the 7812
front panel) accepts Tektronix S-series Sampling Heads.
The type of sampling head selected determines the vertical
input characteristics of the 7S12. The right-hand compart-
ment (labeled PULSE GENERATOR) accepts S-series pulse
generators, trigger recognizers or trigger count-down heads.
The 7S12 has the following features: The vertical de-
flection factors, i.e., millivolts/div and millirho/div, are
from 2 to 500 in a 1-2-5 sequence. The time/div is cali-
brated from 20 ps/div to 1 Us/div in a 1-2-5 sequence. The
DC OFFSET control offsets the display in a +1 V range.
The Hl RESOLUTION switch reduces the waveform noise
and jitter by signal averaging with a corresponding re-
duction of sweep rate. The LOCATE switch increases the
time/div and intensifies a portion of the display to locate
the time window relative to the total waveform. Front
panel outputs include OFFSET OUT (+10 V_ range),
VERTical SIGnal OUT and SWEEP OUT. Modes of sweep
operation include SINGLE sweep, REPetitive sweep,
MANual scan and EXTernal sweep IN.
The TIME-DISTANCE scale is calibrated for round-trip
time measurements of O to 10 Us and one-way distance
measurements up to 4900 feet (1500 meters) air dielectric
or 3200 feet (975 meters) polyethylene dielectric. The
POLY scale may be calibrated for transmission lines which
have a velocity of propagation equal to or greater than that
of polyethylene. The Time-Distance scale may be ordered
with distance calibrated in metric units.
SECTION 1
ELECTRICAL CHARACTERISTICS
Characteristic
Performance Requirement
Supplemental Information
Deflection Factor
Accuracy Within 3%
Range
2 units/div to 500 units/div in a 1-2-5
sequence. Units/div are labeled on the
sampling head.
Units/Div VARIABLE Range Provides continuous coverage from 1
to 770 units/div (mV or mp)
p CAL Range
Allows calibrated reflection coefficient
(p) with pulse generators supplying
from 200 mV to 1 V pulse amplitude.
DC OFFSET Range
Offsets display at least +1 V to —-1V.
OFFSET OUT
Range
At least +10 V to —10 V. OFFSET
OUT = 10X (DC OFFSET) within 2%
Source Resistance 10 k& within 1%
1-1

Characteristics—7S 12
Characteristic
Performance Requirement
Supplemental Information
VERTical SIGnal OUT
Amplitude
200 mV/div of signal display within
2%
VARIABLE control must be in CAL
position.
Source Resistance
10 kQ within .5%
SWEEP OUT
Amplitude 1 V/div of horizontal deflection within
2%
Range OV to greater than 10 V
Source Resistance
10 kQ within 1%
TIME/DIV
Accuracy
Within 3%
Range
20 ps/div to 1 uUs/div in a 1-2-5
sequence
Time/Div VARIABLE Range
Provides continuous coverage to at
least 8 ps/div.
Display Modes
SINGLE Sweep
Each sweep is initiated by pushing and
releasing the START button.
REPetitive Sweep
Normal resolution: sweep rate is
continuously variable from at least 1
sweep in 20 ms to less than 1 sweep in
55,
H| RESOLUTION: sweep rate is con-
tinuously variable from at least 1
sweep in 200 ms to less than 1 sweep
in 50s.
MANual Sweep
Any portion of the display may be
observed by manual operation of the
SCAN control.
EXTernal Input
Deflection Factor
1 V/div within 5% to at least 15 V/div
Input Resistance
100 k2 within 10%
Maximum Input Voltage
150 V (DC + peak AC)
FINE (ZERO SET) Range
Moves an unmagnified waveform at
least .9 div.
1-2
>

Characteristics—7S 12
ELECTRICAL CHARACTERISTICS
SYSTEM PERFORMANCE WITH S-6 AND S-52
Characteristic Performance Requirement Supplemental Information
Risetime 35 ps or less for the incident step, 45 ps
or less for the displayed reflection from a
short-circuited 1 ns test line
Pulse Amplitude At least +200 mV into 50 22
Input Impedance Nominal 50 2
Jitter Less than 10 ps (without signal averaging)
Aberrations Not more than +7%, —7%, total of 10%
P-P within the first 1.8 ns of the step edge
with the reference level at 1.8 ns from the
step edge; not more than +2%, —2%, total
of 4% P-P after 2.5 ns from the step edge
with the reference level at 0.3 us from the
step edge.
TIME-DISTANCE Scale Time scale indicates round-trip time.
Distance scales (AIR and POLY
dielectrics) indicate one-way distance.
The usable TIME-DISTANCE ranges
for TDR measurements are limited by
the S-52 pulse duration.
Accuracy TIME scale within 1% of full scale. Distance scales are calibrated for the
nominal velocity of propagation of the
AIR and POLY dielectrics.
TIME-DISTANCE Multiplier
Karl X1 X10
TIME Range .1 us 1 us 10 us
Maximum of about 150
ns one-way cable delay.
AIR Dielectric Distance 49 feet 490 feet 4900 feet
Range 15 meters 150 meters|1500 meters
Maximum of about 150
feet (46 meters) cable
length.
POLY Dielectric Distance 32 feet 320 feet 3200 feet
Range
9.75 meters |97.5 meters} 975 meters
Maximum of about 100
feet (30 meters) cable
length.
[A] 1-3

Characteristics—7S 12
Characteristic
Performance Requirement
Supplemental Information
PRESET Permits the calibration of the POLY
scale for dielectrics having a velocity
of propagation between those of poly-
ethylene and air.
ELECTRICAL CHARACTERISTICS
SYSTEM PERFORMANCE WITH S-5 AND S-54
Characteristic Performance Requirement Supplemental Information
Risetime 1.5 ns or less for the displayed reflection
from a short-circuited test line
Pulse Amplitude
At least +400 mV into 50 2
Input Impedance
Nominal 50 2
Jitter
Less than 20 ps (without signal averaging)
Aberrations
Not more than +4%, —6%, total of 10%
P-P within the first 17 ns of the step: not
more than +1.5%, —1.5%, total of 3%
after 17 ns.
TIME-DISTANCE Scale
Time scale indicates round-trip time.
Distance scales (AIR and POLY
dielectrics) indicate one-way distance.
TDR events out to 20 us (round-trip
time) may be viewed. This corresponds
to 9800 feet (3000 meters) in AIR
dielectric and to 6400 feet (1950
meters) in POLY dielectric. This
distance is the sum of the displayed
time window (10 us maximum) and
the TIME scale readout (10 us maxi-
mum).
Accuracy
TIME scale within 1% of full scale.
Distance scales are calibrated for the
nominal velocity of propagation of the
AIR and POLY dielectrics.
TIME Range
TIME-DISTANCE Multiplier
X.1 X1 X10
-1 Us 1 ps 10 us
An additional time range may be
viewed.
1-4
—™

Characteristics—7S$ 12
Characteristic
Performance Requirement Supplemental Information
AIR Dielectric Distance
Range
49 feet
490 feet
4900 feet
15 meters 150 meters
1500 meters
An additional distance range may be
viewed (in terms of time).
POLY Dielectric Distance 32 feet 320 feet 3200 feet
Range
97.5 meters 9.75 meters 975 meters
An additional distance range may be
viewed (in terms of time).
PRESET Permits the calibration of the POLY
scale for dielectrics having a velocity
of propagation between those of poly-
ethylene and air.
PHYSICAL CHARACTERISTICS
Characteristic Performance Requirement
“\ Finish Anodized aluminum front panel
Weight
Net 4.7 |b
Domestic Shipping |7.2 Ib
Export Packed 11.7 Ib
Dimensions
Length (ex-
cluding knobs) 13.383 in
Width 5.464 in
Height 4.988 in
ENVIRONMENTAL CHARACTERISTICS
Characteristic Performance Requirement
Temperature
Operating
0°C to +50°C
ENVIRONMENTAL CHARACTERISTICS (cont)
Characteristic
Performance Requirement
Altitude
Operating To 15,000 feet
Non-operating To 50,000 feet
Vibration
Operating 0.025 in P-P displacement at 55 Hz
Shock
Operating To 20 g’s, 1/2 sine, 11 ms duration
Humidity
Non-operating
and Operating
5 cycles (120 hours) to 95% relative
humidity referenced to
MIL-E-16400F (Paragraph 4.5.9
through 4.5.9.5.1, Class 4)
Non-operating
—40°C to +65°C
Transportation
Qualifies under National Safe
Transit Committee test procedure
1A, Category II

NOTES
—
c
c—
-—

—
7812
SECTION 2
OPERATING INSTRUCTIONS
General Information
This section of the manual provides the basic infor-
mation required for operation of the 7S12 TDR/Sampler
including installation, front panel information, and First
Time operation instructions.
The 7S12 is a combined horizontal and_ vertical,
double width sampling unit for use in any 7000-series
Oscilloscope. The 7S12 accepts two plug-in heads, a
sampling head and a generator head, which determine
the characteristics of the TDR system. If a trigger recog-
nizer head such as the S-53 is used in the 7S12 gener-
ator head compartment, general purpose sampling can be
accomplished using the S-53 to trigger the 7512 sweep.
INSTALLATION
The 7812 can be powered by any Tektronix 7000-
series Oscilloscope. Since the 7S12 is a combined hori-
zontal and vertical unit, it must be installed in the
center two compartments of a 7000-series Oscilloscope
containing 4 compartments, or into the right two com-
partments of a 7000-series Oscilloscope containing 3
compartments. A vertical unit such as a 7S11 can be
installed in the left compartment of either Oscilloscope
for dual-trace operation. Then J641 (a fixed shoe
connector) provides a strobe connection to the 7S11.
Three methods of installation are shown in Fig. 2-1.
Part A shows the 7S12 installed in the center two com-
partments of a 7504 Oscilloscope. The 7S11 and samp-
ling heads are shown for TDR and dual-trace use. Part
B shows the 7S12 installed with the 7S11, 7M11, and
sampling heads for General Purpose Sampling and dual-
trace use. Part C shows the 7S12 installed with the
7S11 and sampling heads in the 7403N (or 7503)
3-compartment Oscilloscope for TDR and dual-trace use.
For General Purpose sampling, use the 7M11 outside the
Oscilloscope, and the sampling heads as shown for
installation B.
REV. B, JULY, 1976
Installing the 7S12 in the Oscilloscope
Insert the 7S12 into a vertical and a horizontal com-
partment of a 7000-series Oscilloscope (See Fig. 2-1).
Slide the 7S12 completely into the two compartments.
The 7812 will lock into place with a spring loaded latch
knob.
To install a head into one of the two 7S12 compart-
ments, insert the head into the compartment with the
latch knob free to move until completely in the 7S12.
Then push the latch to lock the head in place. To
remove, pull the latch knob away from the panel, then
pull the unit from the 7S12.
Mating
The 7S12 vertical output amplifier gain must be
matched to the oscilloscope deflection factor for
accurate gain measurements. The VERT GAIN control, a
screwdriver adjustment on the front panel, adjusts the
vertical output amplifier gain of the 7S12. Adjustment
of this VERT GAIN control using the Oscilloscope Cali-
brator as a signal source is shown under First Time
Operation in this section of the manual.
The 7S12 horizontal gain must be matched to the
horizontal deflection factor of the oscilloscope. Hori-
zontal gain is set by the SWEEP CAL adjustment lo-
cated on the 7S12 front panel. The adjustment is made
for full rotation of the SCAN control for 10 divisions
with the MAN button pushed in. The HORIZ POS
adjustment is used to position the spot on the CRT.
The HORIZ POS control is also located on the front
panel. The adjustment method is discussed in First Time
Operation.
CONTROLS AND CONNECTORS
A brief description of the function and operation of
the controls and connectors of the 7S12 follows. Fig.
2-2 shows the 7S12 front panel with a sampling head
and a pulse generator installed.
Vertical Section
DC OFFSET +1 V Positions the display vertically by
applying an internal offset voltage
2-1

Operating Instructions—7S12
Choice of
Sampling Heads
$-1 through S-6
Choice of
Sampling Heads
S-1 through S-6
7s"
ee vent —
2
Choice of
Sampling Heads
$-1 through S-6
the Oscilloscope and use Heads as in (B).
Pulse Generator Heads —
such as S-50, S-52,
and S-54
- Trigger Recognizer
Heads such as
S-51 and S-53
Pulse Generator Heads
such as $-50, S-52,
and §-54
(C) Installed in 7503 (or 7403N) for TDR and dual trace use. For General Purpose Sampling, add the 7M11 (a passive unit) external to
Fig. 2-1. 7S12 Installation Information,
2-2
—™\

Operating Instructions—7$12
FINE
P CAL be OFFSET t1V TIME-DISTANCE
331.0273.00
|
VARIABLE (CAL IN) os
TIME/DIV
FINE
Fig. 2-2. 7S12 front panel.
of up to +1 volt to the sampling
head. The input signal zero refer-
ence (related to the CRT) is the
DC offset voltage instead of
ground. This control permits all
portions of a +1 volt input signal
to be positioned through the
CRT graticule area vertically even
at a deflection factor of 2 units
per division.
Provides fine control of the DC
Offset function. Control is con-
Units/Div
VARIABLE
(CAL IN)
centric with the DC OFFSET +1
V control.
Selects calibrated deflection fac-
tors from 500 units/div to 2
units/div in a 1, 2, 5 sequence.
The actual deflection factor is
determined by the sampling head
used and the ‘‘mV"’, ‘‘mp”
switch.
Provides uncalibrated, continu-
ously variable deflection factor
2-3

Operating Instructions—7S12
mV and mp
pushbuttons
p CAL
HIGH RESOLUTION
VERT GAIN
OFFSET OUT
+10 V 10 kQ
VERT SIG OUT
2V/DIV 10 kQ
Horizontal Section
TIME/DISTANCE
Control
FINE Control
LOCATE Switch
2-4
from less than 0.65 to at least
2.5 times the calibrated setting.
Concentric with the Units/Div
switch.
Permit selecting either mV/Div or
mp/Div as the basic unit of verti-
cal measurement.
Screwdriver adjustment permits
calibrating the display for use
with pulse amplitudes between
200 mV and 1 V.
Reduces the displayed noise by
approximately 10 times and slows
the display rate by 10 times.
Screwdriver adjustment permits
calibration of the vertical output
amplifier gain to match the oscil-
loscope CRT deflection factor.
Miniature connector provides an
output voltage proportional to
the internal DC offset voltage.
Unless otherwise specified on the
sampling head front-panel, the
open circuit voltage at this con-
nector is ten times the internal
DC Offset voltage as set by the
DC OFFSET control. The output
resistance is 10 kQ2.
Miniature connector providing a
real-time reproduction of the sam-
pling display. Permits a non-
sampling type oscilloscope to
monitor the facsimile signal. Out-
put resistance is 10 kQ.
Crank-handle drive positions the
display over the full TIME/
DISTANCE range selected by the
Multiplier switch.
The FINE control provides a 10%
position range with a 10 turn
potentiometer for calibration of
initial step.
Provides a display of the location
of the position control setting on
a display equal to twice the nor-
mal position range. The width of
a brightened portion approximates
the TIME/DIV setting and starts
PRESET Switch
and Control
TIME/DIV Switch
VARIABLE (CAL
IN) Control
TIME/DISTANCE
Multiplier
HORIZ POS
Control
SWEEP CAL
Control
SWEEP OUT
Jack
Variable SCAN
Control
REP Pushbutton
at a point on the displayed sweep
corresponding to the setting of
the TIME/POSITION control.
Provides a means of calibrating
the POLY scale to accommodate
the dielectric constants between
Poly and air.
A 9 position switch used in con-
junction with the 3 position
Multiplier switch. The 27 combi-
nations of TIME/DIV and Multi-
plier switches provide 15 different
calibrated TIME/DIV settings,
from 20 ps/div to 1 us/div, in a
1, 2, 5 sequence.
Provides continuously variable,
uncalibrated time/div by reducing
the time/division. Concentric with
the Multiplier and TIME/DIV
controls.
Provides a X10, X1, X.1
multiplier for the TIME-
DISTANCE tape dial. Switches
Time/Distance ranges. Concentric
with the TIME/DIV and VARI-
ABLE (CAL IN) controls.
range
Screwdriver adjustment for setting
the horizontal position of the dis-
play.
Screwdriver adjustment that sets
the horizontal gain to match the
deflection factor of the oscillo-
scope.
Pin jack providing an output vol-
tage proportional to the hori-
zontal display amplitude. Provides
1 V for each division of display
with an output resistance of 10
kQ.
Provides an internal voltage for
adjusting the scan rate in the
REP mode and SINGLE mode.
Provides the manual scan voltage
in MAN mode and can be used
to calibrate the horizontal gain.
In the EXT mode this control
serves as a variable attenuator.
Provides repetitive scanning of the
display. The scan rate is adjusted
using the variable SCAN control.
=
—

SINGLE
Pushbutton
START
Pushbutton
MAN Pushbutton
EXT INPUT
Pushbutton
EXT INPUT Jack
Correction Memory
Switch
“On (front position)
Normal
(center position)
Off (rear. position)
Provides single scan display for
photographic use. Scan rate is ad-
justed using the variable SCAN
control.
Starts the single scan display after
the SINGLE pushbutton is pushed.
Provides manual operation of the
scan
function using the variable
SCAN control.
Allows scanning the display using
an external signal. In this mode
of operation, the variable SCAN
control serves as a variable gain
control.
Pin jack provides the input facil-
ity for externally scanning the
display. Requires 1 V_ for each
division of display into an input
resistance of 100 kQ.
The three position switch is located
near the top rear edge of the Hori-
zontal card inside the 7S12. The
Correction Memory circuit provides
automatic base line correction for
pulse generator heads and trigger
heads.
This switch position is used when
automatic base line correction is
desired for trigger heads installed in
the Pulse Generator compartment
for DC stabilized sampler applica-
tions.
This is the normal operating switch
position. The Correction Memory
circuit provides automatic base line
correction only for pulse generator
heads installed in the Pulse Gen-
erator compartment.
This switch position disables the
Correction Memory circuit. This
position is also used when a
sampling head gate balance control
is being adjusted.
FIRST TIME OPERATION
General Information
This First Time Operation procedure shows the basic
operation of the 7S12 controls for TDR operation using
the S-52 Pulse Generator Head and the S-6 Sampling
Head. Additional operating information follows the First
Time Operation procedure.
Operating Instructions—7S12
Procedure
1. Insert the 7S12 TDR/Sampler into the center two
compartments of the 7504 Oscilloscope. Any Tektronix
7000-series Oscilloscope may be substituted for the
7504. (See the installation information in this section.)
2. Install the S-52 in the 7S12. Pulse Generator com-
partment.
3. Install the S-6 in the 7S12 Sampling compartment.
4. Set the controls as follows:
7504 Indicator Oscilloscope
A Intensity CCW
B Intensity CCW
Vertical Mode Right
Horizontal Mode A
7812 with S-6 and S-52
(Two center compartments, the right vertical and
the A horizontal compartments)
TIME-DISTANCE dial 0
Multiplier X10
TIME/DIV 1 ys
VARIABLE CAL IN
FINE (ZERO SET) Fully clockwise
REP pushed in
SCAN Midrange
LOCATE pushed in
mV pushed in
mV /Div 100
DC OFFSET (& FINE) Midrange
5. Turn the Oscilloscope Power on. After about 5
minutes warmup time, advance the A Intensity until a
free running trace is observed. Center the trace on the
CRT with the 7S$12 DC OFFSET control.
Adjust VERT GAIN
6. Install a SMA 1 ns coaxial cable (supplied with
the S-52) with a 50 Q termination connector to the S-6
Loop Thru (upper) connector. Install a SMA (3 mm) to
BNC adapter on the Loop Thru (lower) connector. Use
a BNC cable to connect the 0.4 V (into 50 Q) Calibra-
tor Output signal to the adapter installed on the S-6
Loop Thru (lower) connector.
7. Use a small screwdriver to adjust the VERT GAIN
(on the 7S12 front panel) for a square wave display of
4 divisions. Note that the sweep is free running and its
repetition rate is determined by the setting of the
SCAN control. Remove the BNC cable and the BNC to
SMA (3 mm) adapter.

Operating Instructions—7S12
Adjust SWEEP CAL & HORIZ POS
8. Push the MAN button and turn the SCAN control
fully counterclockwise. A spot should be observed at
the left edge of the graticule. If not, use a small screw-
driver to adjust the HORIZ POS control (located on the
7812 front panel) to position the spot at the left edge
of the graticule. Rotate the SCAN control to its fully
clockwise position. The spot should have moved exactly
ten divisions to the right of its previous position. Use a
small screwdriver to adjust the SWEEP CAL control
(located on the 7S12 front panel) for ten divisions of
movement when the SCAN control is turned from one
extreme to the other. Readjust the HORIZ POS as
necessary in this adjustment. Push the REP pushbutton
and set the SCAN control to its approximate midposition.
9. Use 50 {2 semi-rigid cable (u-shaped, supplied with
the 7S12) to connect the S-52 Pulse Output signal to
the Loop Thru (lower) connector on the S-6. The upper
Loop Thru connector is connected to a 1 ns semi-rigid
coaxial cable in part 6.
NOTE
Connectors at both ends of the coaxial cable
should be firmly connected to mating connectors
or accessories. Tighten slightly more ‘than finger
tight using a 5/16 inch wrench. A good connec-
tion is necessary to minimize reflections at the
junctions of connectors.
10. Observe the S-52 waveform shown in Fig. 2-3A. The
positive pulse in the center of the screen is used in the S-52
to automatically reset the tunnel diode bias for the next
pulser trigger from the 7S12. The S-52 output pulse is not
visible on the screen due to the additional 7512 trigger
delay with X10 Multiplier.
Change the 7S12 Multiplier setting to X1 and observe
the S-52 output pulse shown in Fig. 2-3B. The width of the
pulse top will determine the maximum time (round trip
time) of the reflection from the leading edge that can be
observed with X1. Fig. 2-3C shows the leading edge of the
pulse on the X.1 position of the Multiplier. Use the lowest
Multiplier range setting to observe a reflection.
Observing Risetime
11. To observe the leading edge of the S-52 Output
Pulse, set the TIME-DISTANCE Multiplier to X.1, and
the TIME/DIV to a sweep rate desired up to 20 ps; Use
the Time-Distance knob to position the leading edge of
the pulse to the center of the graticule. Use the 20 ps
sweep rate for risetime display (Incident risetime) and
2-6
(A)
(B)
(C)
1244-01
Fig. 2-3. First Time Operation showing Multiplier setting (A) X10,
(B) X1 and (C) X.1.
use the mV/Div VARIABLE knob to set the leading
edge for 5 divisions on the graticule. See Fig. 2-4. Note
that the 5-division points on the display are about one
T, time from reference point 1 for 0% level and about
one T; time from reference point 2 for the 100% level.
REV JAN 1985
ain”

a
Operating Instructions—7S12
Zone
center
Reference
point 2
100% Level
90%
Zone
center 35 ps
10%
0% Level
Reference
point 1
Amplitude
Leading Edge
5 divisions
|
Fig. 2-4. Risetime measurement (T,) information (upper) and typi-
cal risetime display (lower). Note that Reference point 1 and 2 are
selected at the corners where the rate of change of the slope is maxi-
mum (where the radius of curvature is least).
12. To observe the reflected edge (Reflected risetime)
of the S-52 Output Pulse, remove the 50 Q termination
from the end of the 1 ns semi-rigid coaxial cable con-
nected to the S-6 Loop Thru (upper) connector, and
connect a short-circuit termination to the cable.
Change the Time-Distance knob to move the Pulse
leading edge to the left and off the CRT until the re-
flected edge display is centered on the CRT. See the
typical waveform in Fig. 2-5. The Reflected risetime is
measured in the same way as the Incident risetime.
FINE (ZERO SET)
Turn the FINE (ZERO SET) control and note that
the control will change the horizontal position of the
display. This control can be used as a fine position con-
trol, or can be used by the operator as a zero set for
the TIME-DISTANCE dial. Since the reflected edge
Al
100% exx,
90%
Tr = 45 ps or less
10%
0% PP -—P—F-— ered
Fig. 2-5. Reflected risetime display.
represents the end of the 1 ns line where the test line
will be attached, adjust the FINE control so the reflec-
ted edge of the pulse is displayed at the center of the
screen (or a reference point selected by the operator)
with the TIME-DISTANCE dial set to zero.
13. Change the TIME/DIV to .1, and change the
Time-Distance knob to position the reflected pulse to
the graticule centerline. See the typical waveform in Fig.
2-6A.
14. The negative reflection is caused from the short
circuit termination. This reflection therefore has a voltage
reflection coefficient of about —1p or —1000 mp.
15. Remove the short circuit termination. Change the
DC OFFSET control to position the display to show
the positive reflection due to the open line. This reflec-
tion as shown in Fig. 2-6B has a voltage reflection co-
efficient of about +1 p or +1000 mp.
CAL Adjustment
16. Terminate the 1 ns semi-rigid coaxial line with a
50 {2 termination. Change the TIME/DIV to .2 ns, and
change the Time-Distance knob to position the leading
edge of the pulse to the center of the graticule. Push
the mp button in, and set the mp/Div to 200.
17. With a small screwdriver, adjust the 9 CAL con-
trol for a 5 division displayed step amplitude.
Voltage Reflection Coefficient
As shown in Fig. 2-6, the reflection coefficient p
(rho) is taken from the top of the incident pulse from
2-7

Operating Instructions—7S12
Top of Pulse
(A)
Top of Pulse
(B)
Fig. 2-6. Display of a short circuit terminated line (A) and unter-
minated line (B).
the pulse generator. A positive reflection (referenced
from the top of the incident pulse) indicates an imped-
ance greater than the impedance of the line. A negative
reflection indicates an impedance less than the imped-
ance of the line. With a known p, resulting from a resis-
tive load, the resistance of the load can be found by
the following formula:
Impedance Scale Overlays
For each mp amplitude discontinuity displayed on the
CRT, the indicated impedance R{ can be calculated by the
above formula. Impedance Scale Overlays are available for
the CRT face showing direct reading of the Impedance at
each graticule setting for 6 different mp/Div settings. Three
overlays are required to cover 5, 10, 20, 50, 100 and 200
mp/Div
settings. Two sizes of three overlays each are
included in the 7S12 accessories.
2-8
To use the Impedance Scale Overlays, select the overlay
for the mp/Div setting you are using, and install it in posi-
tion over the graticule on the Oscilloscope; read the
impedance values under the proper mp/Div scale listing for
the amplitude of the reflection. Note that the graticule
center is used as the 50 Q reference line.
In addition to impedance values, the overlays include a
POLY distance scale in cm using the 100 ps/Div time. For
further information, read the Time or Distance Measure-
ment Procedures later in this section.
TIME OR DISTANCE MEASUREMENTS
General Information
The TIME-DISTANCE dial setting can be considered to
be a delay in time before the operation of the display time
(except in LOCATE). The display time has 3 multipliers or
ranges, which also multiply the TIME-DISTANCE dial read-
ing. The display time includes a TIME/DIV (magnification
of 1 to 500 times), and a TIME/DIV VARIABLE control
which provides a variable uncalibrated time by reducing the
time per division.
When the LOCATE button is depressed to release (out
position), the displayed time is twice the time (magnifi-
cation of 0.5) labeled at the CCW position of the TIME/
DIV switch. Then the TIME/DIV switch controls the length
of the bright portion of the display to show the position on
the display relative to the pulse edge. The Oscilloscope
readout of the Time/Div will show the correct reading when
the LOCATE button is depressed (in position).
Time/Div
Fig. 2-7 shows the TIME/DIV settings for the Multiplier
settings. The Multiplier changes the scale factor of the
TIME-DISTANCE dial readings. The TIME-DISTANCE dial
readings are not generally used when in LOCATE. The
LOCATE position display is intensified by the Display Win-
dow time as controlled by the TIME/DIV and the TIME/
DIV VARAIBLE controls. The Display Window time be-
comes the normal display time when the LOCATE button
is depressed.
Fig.
2-8
shows
the
Display
Window
time
for
two
settings
of
the
TIME/DIV
control
and
three
settings
of
the
TIME-
DISTANCE
dial.
With the TIME/DIV setting CCW (.1 us/Div), shown in
Fig. 2-8A, the TIME-DISTANCE dial is set for a Multiplier
of X1. Note that a delay from zero time to 1 us dial setting,
with the additional time of the Display window results in a
total of 2 us from the zero time. Accordingly, the duration
of the Pulse Output from the Pulse Generator head must be
at least 2 us. Use of the Multiplier of X1 with the S-52 is

Operating Instructions—7S12
Multiplier LOCATE CCW<———_—_______—_—_——- TIME/DIV ———————————_> CW
(Magnification)
X1 X2 X5 X10 X20
X50 X100 X200
500
Multiplies
50 ns
5 ns
.2 Us 20 ns
2 ns
10 ns
Ins
-1 us
10 ns
Ins
5 ns 2 ns
Time-Distance ns
50 ps
.2ns
20 ps
dial reading
5 ns .2ns -Tns
Displayed
Time/Div in
LOCATE
VARIABLE control
(reduces Time/Div)
TIME/DIV
control
Multiplier
control
Fig. 2-7. Time/Div control information.
limited due to the short duration S-52 output pulse, shown mined more readily than from the TIME-DISTANCE dial.
in Fig. 2-3B. Also, use of the X10 Multiplier is restricted Measure the time separation on the CRT screen, note the
due to the 7812 pulser trigger delay and the S-52 short horizontal calibration (TIME/DIV) and use Table 2-1 to
pulse. Using the Multiplier of X10 with a pulse generator determine the distance separation. This table is an aid in
head with a long pulse duration (for example S-54 with a making measurements for short distances, where the TIME-
pulse duration of 25 us) the total time of about 20 us is DISTANCE dial’s resolution is limited. The column “‘Separ-
available.
As the TIME/DIV is changed toward the CW positions, TABLE 2-1
the Display Window time is less and the total time from On Seren Time-vs, Distance: [Senaration}
zero is less, as shown in Fig. 2-8B.
Time or Distance Measurement Procedures Time is for round trip, and Distance is
for one way, in inches or cm/div.
Procedures for Time or Distance measurements can be
shown in three general methods: TIME/DIV Separation in Separation in Separation in
. AIR POLY PRESET (Spans
(A) On the screen, where measurement points are lo- AIR to POLY)
cated a short distance apart.
(B) Between two points on the TIME-DISTANCE 20 ps/Div .12 inch/Div .08 inch/Div
dial. -3 cm/Div -2 cm/Div
50 ps/Div} .3inch/Div .2 inch/Div
(C) From dial zero, on the TIME-DISTANCE dial. 75 cm/Div 5 cm/Div
100 ps/Div| .6 inch/Div .4 inch/Div
A) On the Screen. The distance between two measure-
fd Eins the Se 1.5 cm/Div 1 cm/Div
ment points or discontinuities on the screen may be deter-
2-9

Operating Instructions—7$12
oo Windows
pa a Ne ce fe me a ce ee ee ee oe ee
| Ee
| |
! |
I
|
1 |
| !
| |
s |
TIME 0 | 5 us | 1 us | (1.5 us) (2 us)
AIR o| 246 feet | 492 feet |
POLY 0| 162 feet | 324 feet |
Time-Distance
dial settings’
(A) Time/Div set CCW.
Display
windows
e @
TIME 0] 5 us | Tus | (1.5 ys) (2 ys)
AIR 0| 246 feet | 492 feet |
POLY o| 162 feet | 324 feet |
Time
Distance
|
dial settings’
(B) Time/Div-set CW.
'The Time-Distance dial setting times the Multiplier setting of X .1, 1, or 10 will indicate the round trip time or the one way distance,
Note: Optional dial calibrated in meters.
Fig. 2-8. Effect of the Time/Div setting in relation to the three settings of Time-Distance dial. The time or distance represented in the time
windows shown is determined by the Multiplier setting.
ation in PRESET (Spans AIR to POLY)” can be filled in or
noted by the operator. The PRESET distances will be deter-
mined by the setting of the PRESET control (a screwdriver
adjustment on the front panel) when the PRESET button is
pushed in. The adjustment is set by the operator for cable
propagation velocities between air and Poly.
(B) Two dial points. This method uses the net dial read-
ing to determine the distance between the two points or
discontinuities. Observe one of the two discontinuities and
note its reference point on the screen (or set the FINE
control to position the discontinuity to the center or refer-
ence point on the CRT). Record the Time-Distance dial
2-10
setting (TIME, POLY, or PRESET POLY). Change the
Time-Distance knob to position the other discontinuity to
the same reference point on the CRT. Record the TIME-
DISTANCE setting. Subtract one recorded reading from the
other, to determine the net dial reading. The net dial read-
ing, times the Multiplier setting, will result in the round trip
time or one way distance between the two discontinuities.
(C) From dial zero. In order to make measurements
directly from the TIME-DISTANCE dial, the zero point
must be determined. The FINE (ZERO SET) control is
useful for a fine positioning control, and to set the dial
zero.
—\