Tektronix 7B85 User manual

Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon 97077
INSTRUCTION MANUAL
Serial Number
Scans by ArtekMedia O 2006
First Printing, DEC 1975

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Copyright @ 1975 by Tektronix, Inc., Beaverton,
Oregon. Printed intheUnitedStatesof America. All
rights resewed.Contentsof thispublicationmaynot
be reproduced in any form without permission of
Tektronix, Inc.
U.S.A. and foreign TEKTRONIX products covered
by
U.S. andforeignpatentsand/orpatentspending.
TEKTRONIX isaregisteredtrademarkof Tektronix,
Inc.
Scans by AttekMedia O 2006

7B85 Operators
TABLE OF CONTENTS
PAGE
LIST OF ILLUSTRATIONS
.................... ii
LIST OF TABLES ........................... ii
SAFETY SUMMARY
........................ iii
SECTION
1 OPERATING INSTRUCTIONS
INSTALLATION
..................... 1-1
CONTROLS. CONNECTORS.
AND INDICATORS
.................... 1-1
FUNCTIONAL CHECK ................. 1-1
Setup Procedure
.................... 1-4
Sweep Functions
.................... 1-4
NORMALSWEEP
................. 1-4
DELAYINGAND DELAYEDSWEEP
.... 1-4
A (DIFFERENTIAL)TIME ........... 1-5
Triggering Functions
................. 1-5
GENERAL OPERATING INFORMATION
.... 1-6
Triggering Switch Logic
............... 1-6
Triggering Modes .................... 1-6
P-P AUTO
...................... 1-6
AUTO
......................... 1-6
NORMAL
...................... 1-6
SINGLE SWEEP
.................. 1-6
Trigger Coupling
.................... 1-7
AC
........................... 1-7
AC LF REJ
..................... 1-7
AC HF REJ
..................... 1-7
DC
........................... 1-7
Trigger Source
..................... 1-7
INTERNAL
..................... 1-7
PAGE
LINE ......................... 1-7
EXTERNAL
..................... 1-7
Trigger Slope
...................... 1-7
Trigger Level
...................... 1-7
............... Horizontal Sweep Rates 1-9
.................. Time Measurement 1-9
Sweep Magnification
................. 1-9
................... Variable Hold Off 1.10
................ Delay-Time Operation 1.10
................... A Time Operation 1.10
A TIME OPERATION INA
DUAL-BEAMOSCILLOSCOPE
MAINFRAME
................... 1.12
Mainframe Operating Modes
............ 1.12
APPLICATIONS
........................ 1.13
DELAYED-SWEEP MEASUREMENTS
....... 1.13
Time-Interval Measurements
(Delay-TimeMode)
.................. 1.13
Differential Time-Interval Measurements
(A Time Mode) ..................... 1.14
Delayed-SweepMagnification ........... 1.15
Triggered Delayed-SweepMagnification
..... 1.18
INDEPENDENT TIME-IIV'TERVAL
MEASUREMENTS .................... 1.18
SECTION
2 SPECIFICATION
STANDARD ACCESSORIES
............... 2-4
SECTION
3 INSTRUMENTOPTIONS
CHANGE INFORMATION
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7B85 Operators
FIGURE
NO.
Frontis-
piece
1-1
1-2
LIST OF ILLUSTRATIONS
PAGE FIGURE
NO.
7885 Features .................... iv
............ Locationof release latch. 1-1
Front-panelcontrols, connectors,
................... and indicators. 1-2
Effectsof LEVELcontrol and SLOPE
switch on crt display
............... 1-8
Area of graticule used for most accurate
time measurements
................ 1-9
Effect of sweep magnifier on crt display
. . 1-9
(A)Delaying-sweepdisplay producedby
7885 in the A horizontal compartment.
(B) Delayed-sweepdisplay producedby
companion time-baseunit inthe B hori-
zontal compartment.
.............. .l-10
Typical
A (differential)Time Operation. . .l-11
TABLE
NO.
PAGE
LIST OF TABLES
Measuringtime intervalsfrom a triggering
event (start of sweep) toany point on
a
..................... waveform. .l-14
Measuring rise time, fall time, period,
frequency, or pulse width inthe
A (dif-
.............. ferential) time mode .l-15
Magnifying
a selected segment of the
delaying (A)sweep inthe delay-time
mode with mainframe alternate or
........ chopped horizontal operation .l-16
Time-interval measurementsin the
delay-time and
A (differential)time
mode with mainframe alternate or
chopped operation.
............... .l-17
Examiningan event that occurs within
aselected time interval after
a known
..... delay time in the delay-time mode .l-18
........... 7B85 dimensionaldrawing 2-4
PAGE
2-1 Electrical Characteristics. ............ 2-1
2-2 Environmental Characteristics
......... 2-4
............. 2-3 PhysicalCharacteristics. 2-4
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7B85 Operators
SAFETY SUMMARY
This manualcontains safety informationwhich the user must follow toensure safe operation of this instrument. WARIUING
information is intended to protect the operator, CAUTION information is intendedto protect the instrument. The following
are general safety precautionsthat must be observedduring all phases of operation.
Ground the Instrument
Toreduce electrical-shock hazard, themainframe (oscilloscope)chassis must beproperly grounded. Refer to the mainframe
manual forgrounding information.
Do NotOperate in Explosive Atmosphere
Donot operate this instrument in an area whereflammablegases or fumesare present. Such operation could cause an
explosion.
Avoid Live Circuits
Electrical-shock hazards arepresent in this instrument. Theprotective instrument coversmust notbe removed by operating
personnel. Component replacementand internal adjustments must be referred to qualifiedservicepersonnel.
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7B85 Operators
7685 Features
The 7B85 Delaying Time-Baseunit providescalibrated sweep rates from 5 seconds to 10 nanoseconds and triggering to400
megahertz for 7700-, 7800-, and 7900-seriesoscilloscopes. The XI0 Magnifier increases each sweep rate by afactor of 10
and a VARIABLE control allows continuously variable sweep rates betweencalibrated steps. Variable hold off and alpha-
numeric readout are provided. Also, when operating in the AUTO TRIGGERING MODE,
a bright baseline trace is displayed
in the absence of atrigger signal.
Other features include independent sweep operation or continuously variable sweep delay (DELAYTIME) and differential
sweep delay
(A TIME) with acompanion time-base unit. Delay time or differential delay time readout is displayed on the
mainframe cathode-ray tube.
Scans by ArtekMedia O 2006

Section 1-7B85
OPERATING INSTRUCTIONS
The 7885Time-Base unit operates with aTektronix 7700-, 7800-, or 7900-seriesoscilloscope mainframe and a 7A-series
amplifier unit to form acomplete oscilloscopesystem. This section describes the operation of the front-panel controls and
connectors, provides general operating information, a functional check procedure, and basic applications for this instrument.
IIVSTALLATION CONTROLS, CONNECTORS, AND INDICATORS
The time-baseunit is designed to operate in the horizontal All controls, connectors, and indicators required for the
plug-incompartment of the mainframe. This instrument operation of the time-base unit are located on the front
can also be installed in avertical plug-incompartment to panel. Figure 1-2shows and providesa brief description of
provide avertical sweep on the crt. However, when used in all front-panel controls, connectors, and indicators. More
this manner, there are no internal triggering or retrace detailed information is given in the General Operating
blanking provisions, and the unit may not meet the specifi- Instructions.
cations given in Section 2.
To install the unit in a plug-incompartment, push it in until
itfits firmly into the compartment. The front panel of the
unit should be flush with the front panel of the mainframe.
Even though the gain of the mainframe is standardized, the
sweep calibration of the unit should be checked when in-
stalled. The procedure for checking the unit
is given under
Sweep Functions in the Functional Check procedure inthis
section.
To remove the unit, pull the release latch (see Figure 1-1)
todisengage the unit from the mainframe, and pull it out of
the plug-in compartment.
LEVEL
rwe o
TRIGGERING 11'1
."TO LC u "El Llll
" I
$In I
RELEASE
LATCH
FUNCTIONAL CHECK
The following procedures are provided for checking basic
instrument functions. Refer tothe description of the con-
trols, connectors, and indicators while performing this pro-
cedure. If performing the functional check procedure
reveals a malfunction or possible improper adjustment, first
check the operation of the associated plug-in units, then re-
fer to the instruction manual for maintenanceand adjust-
ment procedures.
Setup Procedure
1. Install the 7B85 inthe A horizontal compartment of the
mainframe.
2. Install an amplifier plug-in unit in avertical compart-
ment.
3. Set the 7B85 controls as follows:
SLOPE
MODE
COUPLING
SOURCE
B DELAY MODE
TRACE SEP
POSITION
TIMEIDIV
VARIABLE
(CAL IN)
HOLDOFF
MAG
(+)
P-P AUTO
AC
INT
INDEPENDENT
OFF (fullyclockwise)
Midrange
1 ms
Calibrated (Pushed in)
MIN (fully counter-
clockwise)
XI (pushedin)
Fig. 1-1. Location of release latch.
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Operating Instructions-7B85
Fig. 1-2. Front-panelcontrols, connectors, and indicators.
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Operating Instructions-7685
TRIGGERING
a LEVELControl-Selects a pointonthetrigger signal where triggering occurs.
@ SLOPE Switch- Permits sweep tobetriggered onnegative- or positive-goingportionsof thetrigger signal.
@ READY Indicator-Illuminates when sweep circuit isarmed (SINGLE SWEEP Mode).
@ TRIG'D Indicator-Illuminates when thedisplay is triggered.
@ MODE Pushbuttons-Selects theoperating mode of the triggering circuits.
@ COUPLING Pushbuttons-Selects the method of coupling thetrigger signal totriggering circuit.
@ SOURCE Pushbuttons-Selects source of thetrigger signal.
SWEEP
@ POSITIONControl-Provides horizontal positioning.
@ FINEControl-Provides precise horizontal positioning.
@ HOLDOFF Control-Permits holdoff periodtobe varied toimprovetriggeringstability of repetitivecomplex waveforms.
@ MAG Pushbutton-Selects XI0magnifiedor unmagnified sweep.
@ TlMElDlV Switch-Selects thesweep rateof thesweep generator.
13
VARIABLE Control and CALSwitch-Selects calibrated or uncalibrated sweep rates. Uncalibratedsweep ratescan be
0 continuously reducedtoat least the sweep rateof the next slower position.
14
SWP CALAdjustment-Compensates for basic timing changes due tothedifferences insensitivity of mainframes inwhich
O the 7885 may be used.
EXTERNAL TRIGGER INPUT
@ EXTTRIG ATTENUATOR-Selects attenuation factor for external trigger signals.
@ EXTTRlG INConnector-Connector (BNCtype1 provides input for external trigger signals.
SWEEP MODE
B DELAYMODE Pushbuttons-Selects independent or delaying sweep operation. Inthe B STARTSAFTER DLYand
B TRIGGERABLE AFTER DLYdelayingsweep modes, the DELAY TlME and
A
TlMEfunctions are activated. There
will be a
2 division vertical shift of thetrace when switchingfrom INDEPENDENTtoB STARTSAFTER DELAY.
DELAYTIME
18
DELAYTlME Control-Provides variable delay timebefore thestart of thedelayed sweep producedbycompanion time-
base unit.
19
TRACE SEP Controland Switch-Enables A TlME functions and provides vertical separation of thedelayed sweep
O traces (A TIME operation,.
A TlME Control-Provides differential timemeasurements between 2 selected intensified zones onthedelaying sweep
trace. Twodelayed sweep traces corresponding tothe intensified zones are displayed bythe companion time-base unit.
Differentialtime isdisplayed onthe crt readout.
Fig. 1-2. Front-panelcontrols, connectors, and indicators (cont.).
REV. A, APR. 1977
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Operating Instructions-7085
4. Turn on the oscilloscope and allow at least 20 minutes
warmup.
5. Set the mainframe vertical and horizontal modesto dis-
play the plug-in units used and adjust the intensity and
focus for awell-defined display. See the oscilloscope main-
frame and amplifier unit instruction manuals for detailed
operating instructions.
Sweep Functions
NORMAL SWEEP. Perform the following procedure to
obtain anormal sweep and to demonstrate the function of
the related controls:
1. Perform the precedingSetup Procedure.
2. Connect a 0.4-volt, l-kilohertz signal from the main-
frame calibrator to the amplifier unit input.
3. Set the amplifier unit deflection factor for 4 divisions of
display.
4. Adjust the LEVELcontrol for astable display.
5. Turn the POSITION control and note that the trace
moves horizontally.
6. Turn the FINE control and note that the display can be
precisely positioned horizontally.
7. Check the display for one complete cycle per division. If
necessary, adjust the front-panel SWP CAL screwdriver ad-
justment for one complete cycle per division over the
center 8 graticule divisions. Be sure that the timing of the
mainframe calibrator signal is accurate to within 0.25%
(+20 to +30° C).
8. Press to release the VARIABLE (CAL IN)control. Turn
the VARIABLE (CAL IN)control fully counterclockwise
and note that the displayed sweep rate changes to at least
the next slower TIMEIDIV switch setting (i.e., 2 milli-
secondsldivision). Press the VARIABLE (CAL IN)knob in
tothe calibrated position
MAGNIFIED SWEEP. Perform the following procedure to
obtain a XI0 magnified display and to demonstrate the
function of the related controls:
1. Obtain aone cycle per division display as described in
the precedingNormal Sweep procedure.
2. Press to releasethe MAG button (X10). Note that the
unmagnified display within the center division of the grati-
cule is magnified toabout 10divisions.
3. Press the MAG button (XI
).
DELAYINGAND DELAYEDSWEEP. Perform the follow-
ing procedure to obtain delaying- and delayed-sweep
displays and to demonstrate the function of the related
controls. To obtain a delayed-sweepdisplay, acompanion
time-baseunit must be installed inthe B horizontal com-
partment of the mainframe.
1. Obtain a display as described inthe preceding Normal
Sweep procedure.
2. Press the BSTARTS AFTER DELAY button.
3. Set the mainframe horizontal mode for chopped
operation.
4. Set the companion time-baseunit sweep rate for 0.1 mil-
lisecond/division, and triggering for p-p auto mode, ac
coupling, internal source, and
+ slope.
5. Adjust the mainframe B sweep intensity and check for
an intensified zone about 1division wide on the delaying
(A)sweep display. Also note that the delayed (B)sweep
providesan expandeddisplay of the intensified portionof
the delaying (A)sweep.
6. Position the start of the delaying (A)sweep to the left
edge of the graticule.
7. Adjust the DELAY TlME control for a crt readout
(bottomdivision of crt graticule) of 5.000 ms. Check that
the left edge of the intensified zone
is at the graticule
center line.
8. Set the 7B85 TIMEIDIV switch to
.5 ms and the delay-
ed (B)sweep unit sweep rate to 20 microseconds/division.
9. Turn the DELAY TlME control fully counterclockwise
to position the intensifiedzone near the front corner of the
first square-wave cycle. Press the B TRIGGERABLE
AFTER DLY button and check that the intensified zone
moves to the front corner of the next displayed square
wave.
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Operating Instructions-7B85
A (DIFFERENTIAL) TIME. Perform the following proce-
dure to obtain a
A (differential)time display and to demon-
strate the function of the relatedcontrols:
1. Obtain
a delaying (A)and delayed (B)sweep display as
describedinsteps 1through 4 of the precedingDelaying
and DelayedSweep procedure.
2. Turn the TRACE SEP control counterclockwiseout of
the OFF (detent) position.
3. Set the DELAY TIME and
A TIME controls to the fully
counterclockwise position. Check for two delayed (B)
sweeps and note that the crt readout (bottomright of crt)
is 0.000 ms.
4. Slowly turn the
A TIME control clockwise and note that
a second intensified zone moves across the delaying (A)
sweep display and the crt readout indicatesthe differential
time between the left edge of the stationary intensified
zone and the left edge of the second intensified zone. Also
note that the lower delayed (B)sweep is an expanded dis-
play of the second intensified zone.
Triggering Functions
Perform the following procedure to obtain a triggered
sweep and to demonstrate the functions of the related
controls:
1. Obtain
a display as described in the precedingNormal
Sweep procedure.
2. Press the AUTO MODE button and turn the LEVEL
control fully counterclockwise to obtain
a free-running
sweep.
3. Slowly turn the HOLD OFF control clockwiseand note
that
a stable display can be obtained at several positionsof
the HOLD OFF control. Return the HOLD OFF control to
the fully counterclockwise (MIN)position.
NOTE
TheHOLD OFF control varies the sweep hold-
off time which effectively changes the repetition
rate of the horizontalsweep signal. However, its
primary function is to obtain astable display of
complex waveforms which are otherwisedifficult
to trigger.
4. Press the AC, AC HF REJ, and DC COUPLING buttons
for boththe
+ and - positions of the SLOPE switch and
check for
a stable display (LEVELcontrol may be adjusted,
if necessary, to obtain astable display).
5. Apply the 0.4-volt, 1 kilohertz signal from the main-
frame calibrator tothe amplifier unit and to the EXTTRIG
INconnector.
6. Press the EXTSOURCE button and set the amplifier
unit deflection factor for a4-division display.
7. Press the AC, AC HF REJ, and DC COUPLING buttons
for boththe
+ and - positions of the SLOPE switch and
check for
a stable display (LEVELcontrol may be adjusted,
if necessary,for astable display).
8. Press the AC COUPLING, INTSOURCE, and NORM
MODE buttons. Adjust the LEVEL control for
a stable
display.
9. Press the AUTO MODE buttonand adjust the LEVEL
control for
a free-runningdisplay.
10. Press the NORM MODE button and check for no
display.
11. Adjust the LEVEL control for
a stable display and
press the SINGLE SWP MODE button.
12. Note that one trace occurs when the RESET MODE
button is pressed.
13. Disconnectthe mainframecalibrator signal from the
amplifier unit input and press the RESET MODE button.
Check for no display and note that the READY indicator
is lit.
14. Note that one trace occurs and that the READY indi-
cator extinguisheswhen the mainframecalibrator signal is
reconnectedto the amplifier unit input.
Scans by ArtekMedia O 2006

Operating Instructions-7B85
GENERAL OPERATING INFORMATION
Triggering Switch Logic
The MODE, COUPI-ING, and SOURCE push buttons of the
TRIGGERING switches are arranged inasequence which
places the most-oftenused position at the top of each series
of push buttons. With this arrangement, astable display can
usually be obtained by pressing the top push buttons: P-P
AUTO, AC, INT.When an adequate trigger signal
is applied
and the LEVELcontrol
is correctly set, the unit is triggered
as indicated by the illuminated TRIG'D light. If the
TRIG'D light is not on, the LEVEL control
is either at a
setting outside the range of the trigger signal applied tothis
unit from the vertical unit; the trigger signal amplitude
is
inadequate, or its frequency is below the lower frequency
limitof the AC COUPLING switch position. Ifthe desired
display is not obtained with these buttons pushed in, other
selections must be made. Refer to the following discussions
or the instruction manuals for the associated oscilloscope
mainframe and vertical unit(s) for more information.
Triggering Modes
The MODE push-buttonswitches select the mode inwhich
the sweep is triggered.
P-P AUTO. The P-PAUTO MODE providesatriggered dis-
play at any setting of the LEVELcontrol whenever an ade-
quate trigger signal is applied. The range of the LEVEL
control inthe P-PAUTO MODE
is between approximately
10%and 90% of the peak-to-peakamplitude of the trigger
signal. The LEVELcontrol can be set so that the displayed
waveform starts at any point within this range on either
slope. The trigger circuits automatically compensate for a
change in trigger signal amplitude. Therefore, if the LEVEL
control is
set to start the waveform display at acertain per-
centage point on the leadingedge of a low-amplitudesignal,
ittriggers at the same percentage point on the leadingedge
of a high-amplitude signal if the LEVEL control is not
changed. When the trigger repetition rate is outside the
parameter given inthe Specification section, or when the
trigger signal is inadequate,the sweep free runs at the rate
indicated by the TIMEIDIV switch to produce a bright
base-line,reference trace (TRIG'D light off).When an ade-
quate trigger signal is again applied, the free-runningcondi-
tion ends and atriggered display
is presented.
The P-PAUTO MODE is particularly useful wher~observing
aseries of waveforms, since it is not necessary to reset the
LEVEL control for each observation. The P-P AUTO
MODE is used for most applications because of the ease of
obtaining a triggered display. The AUTO, NORM, and
SINGLE-SWP MODE settings may be used for special
applications.
AUTO. The AUTO MODE provides a triggered display
with the correct setting of the LEVELcontrol whenever an
adequatetrigger signal
is applied (see Trigger Level discus-
sions). The TRIG'D light indicates when the display is
triggered.
When the trigger repetition rate
is outside the frequency
range selected by the COUPLING switch or the trigger sig-
nal is inadequate,the sweep free runs at the rate indicated
by the TIMEIDIV switch (TRIG'D indicator off). An ade-
quate trigger signal ends the free-runningcondition and a
triggered display
is presented. The sweep also free runs at
the rate indicated by the TIMEIDIV switch when the
LEVELcontrol is at asetting outside the amplitude range
of the trigger signal. This type of free-runningdisplay
is use-
ful when
it is desired to measure only the peak-to-peak
amplitude of a signal without observing the waveshape
(suchas bandwidth measurements).
NORMAL. The NORM MODE provides atriggered display
with the correct setting of the LEVEL control whenever an
adequate trigger signal
is applied. The TRIG'D light indi-
cates when the display is triggered.
The normal trigger mode must be used to produce triggered
displayswith trigger repetition rates below about 30 hertz.
When the TRIG'D light
is off, no trace is displayed.
SINGLE SWEEP. When the signal to be displayed is not re-
petitive or varies in amplitude, waveshape, or repetition
rate, aconventional repetitive type display may produce an
unstable presentation. Under these circumstances, astable
display can often be obtained by using the single-sweep
feature of this unit. The single-sweepmode is also useful to
photograph non-repetitive or unstabledisplays.
To obtain asingle-sweepdisplay of arepetitive signal, first
obtain the best possibledisplay in the NORM MODE. Then,
without changing the other TRIGGERINGcontrols, press
the SINGLE SWP RESET button. A single trace
is present-
ed each time this button
is pressed. Further sweeps cannot
be presented until the SINGLE SWP RESET button is
pressed again. Ifthe displayed signal is acomplex waveform
composed of varying amplitude pulses, successive single-
sweep displays may not start at the same point on the wave-
form. To avoid confusion due to the crt persistence, allow
the display todisappear before pressing the SINGLE SWP
RESET buttonagain. At fast sweep rates,
it may be diffi-
cult toview the single-sweepdisplay. The apparent trace in-
tensity can be increased by reducing the ambient light level
or by usingaviewing hood as recommendedinthe main-
frame instruction manual.
When using the single-sweep mode to photograph wave-
forms, the graticule may have to be photographed separate-
ly inthe normal manner to prevent over-exposingthe film.
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OperatingInstructions-7B85
Be sure the camera system is well protected against stray
light, or operate the system in
a darkened room. For repe-
titive waveforms, press the SINGLE SWP RESET button
only once for each waveform unless the signal is completely
symmetrical. Otherwise, multiple waveforms may appear on
the film. For randomsignals, the lens can be left open until
the signal triggers the unit. Further informationon photo-
graphic techniques is given in the appropriate camera in-
struction manual.
Trigger Coupling
The TRIGGERING COUPLING push buttons select the
method inwhich the trigger signal
is connected tothe trig-
ger circuits. Each position permits selection or rejection of
some frequency components of the signal which triggers
the sweep.
AC. AC COUPLING blocksthe dc component of the trig-
ger signal. Signals with low-frequency components below
about
30 hertz are attenuated. Ingeneral, AC COUPLING
can be used for most applications. However, ifthe signal
contains unwantedfrequency componentsor if the sweep is
to be triggered
at a low repetition rate or dc level, one of
the other COUPLING switch positionswill provide
a better
display.
AC LF REJ. AC LF REJ COUPLING rejects dc, and atten-
uates low-frequency trigger signals below about
30 kilo-
hertz. Therefore, the sweep
is triggered only by the higher-
frequency components of the trigger signal. This position is
particularly useful for providing stable triggering if the
trigger signal contains line-frequencycomponents. Also, the
AC LF REJ position providesthe best alternate-modever-
tical displays
at fast sweep rates when comparing two or
more unrelatedsignals.
AC HF REJ. AC HF REJ COUPLING passes all low-
frequency signals betweenabout 30 hertz and 50 kilohertz.
Dc is rejected and signals outside the above range are atten-
uated. When triggering from complex waveforms, this posi-
tion
is useful to provide a stable display of the low-
frequency components.
DC. DC COUPLING can be used to providestable trigger-
ing from low-frequency signals which would be attenuated
inother COUPLING switch positions. DC COUPLING can
be used to trigger the sweep when the trigger signal reaches
a dc level set by the LEVELcontrol. When using internal
triggering, the setting of the vertical unit position control
affects the triggering point.
Trigger Source
The TRIGGERING SOURCE push buttons select the
source of the trigger signal which
is connected tothe trigger
circuits.
INTERNAL. The INT position connects the trigger signal
from the vertical plug-in unit. Further selection of the in-
ternal trigger signal may be provided by the vertical plug-in
unit or by the mainframe;see the instruction manuals for
these instrumentsfor more information. For most applica-
tions, the internal source can be used. However, some appli-
cations requirespecial triggeringwhich cannot be obtained
in the INTposition. Insuch cases, the LlNE or EXTposi-
tions of the SOURCE switches must be used.
LINE. The LlNE position connects
a sample of the power-
line voltage from the mainframetothe trigger circuit. Line
triggering is useful when the input signal
is time-related
(multipleor submultiple) tothe line frequency. Itis also
useful for providing
a stable display of a line-frequency
component in
a complex waveform.
EXTERNAL. The EXT position connectsthe signal from
the EXTTRIG IN connector tothe trigger circuit. The ex-
ternal signal must be time-related to the displayed wave-
form for
a stable display. An external trigger signal can be
used toprovide
a triggered display when the internal signal
is either too low inamplitude for correct triggeringor con-
tains signal components on which triggering
is not desired.
It is also useful when signal tracing in amplifiers, phase-shift
networks, wave-shapingcircuits, etc. The signal from
a
single point in the circuit can be connected to the EXT
TR lG INconnector through
a probe or cable. The sweep is
then triggered by the same signal
at all times and allows am-
plitude, time relationship, or waveshape changes of signals
at various points in the circuit to be examined without
resettingthe TRIGGERING controls.
The
+I0 push button attenuatesthe external trigger signal
by
a factor of 10. Attenuation of high amplitude external
trigger signals is desirable toincrease the effective range of
the LEVELcontrol.
Trigger Slope
The TRIGGERING SLOPE switch (concentric with the
TRIGGERING LEVEL control) determines whether the
trigger circuit responds on the positive- or negative-going
portion of the trigger signal. When the SLOPE switch is in
the
(+) (positive-going)position, the display starts on the
positive-goingportion of the waveform (see Figure
1-31.
When several cycles of a signal appear inthe display, the
setting of the SLOPE switch is often unimportant.However,
if only a certain portion of a cycle is to be displayed, cor-
rect settingof the SLOPE switch is important to provide
a
display that starts on the desired slope of the input signal.
Trigger Level
The TRIGGERING LEVELcontrol determines the voltage
level on the trigger signal at which the sweep is triggered.
When the LEVELcontrol is set in the
+ region, the trigger
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Operating Instructions-7B85
TRIC'D
BLOB0
LEVEL
(SLOPE)
(LEVEL)
CRT DISPLAY
OBTAINEDWlTH
SLOPE SWITCH
SET TO POSITIVE
(+I
TRIC'D
8LopE LEVEL •
TRIC'D
SLOPE
LEVEL .
CRT DISPLAY
OBTAINED WITH
I SLOPE SWITCH
SET TO NEGATIVE
(-1
TRI6'D
SLOPE
LEVfL .
Fig. 1-3. Effects of LEVEL control and SLOPE switch on crt display.
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Operating Instructions-7B85
circuit responds at a more positive point on the trigger sig-
nal. When the LEVEL control is set in the
- region, the
trigger circuit responds at a more negative point on the
trigger signal. Figure 1-3 illustrates this effect with different
settingsof the SLOPE switch.
To set the LEVEL control, first select the TRIGGERING
MODE, COUPLING, SOURCE, and SLOPE. Then set the
LEVEL control fully counterclockwise and rotate itclock-
wise untilthe display starts at the desired point. Less selec-
tion of the triggering level is available as the trigger signal
frequency exceeds 150 megahertz.
Horizontal Sweep Rates
The TIMEIDIV switch providescalibrated sweep rates from
5 secondsldivision to 10 nanoseconds/division in a 1-2-5
sequence. The VARIABLE TIMEIDIV control must be in
the calibrated position and the MAG switch set to XI to
obtain the sweep rate indicated by the TIMEIDIV switch.
However, the mainframe crt readout will display the appro-
SECOND-VERTICAL TENTH-VERTICAL
LINE LINE
I
I
I I
p-TIME MEASUREMENT -4
AREA
C1752-06
priate sweep rate.
Fig. 1-4. Area of graticule used for most accuratetime measure-
ments.
The VARIABLE TIMEIDIV control includes atwo-position
switch todetermine if the sweep rate is calibrated, or un-
calibrated. When the VARIABLE control is pressed in, it is
inoperative and the sweep rate is calibrated. When pressed
and releasedoutward, the VARIABLE control is activated
for uncalibrated sweep rates, to at least the sweep rate of
the next slower position.
A calibrated sweep rate can be obtained in any position of
the VARIABLE control by pressing in the VARIABLE con-
trol. This feature is particularly useful when aspecific un-
calibrated sweep rate has been obtained and it is desired to
switch between calibrated and uncalibrated displays.
Time Measurement
When making time measurements from the graticule, the
area between the second and tenth vertical lines of the gra-
ticule provides the most linear time measurements (see
Figure 1-4).Position the start of the timing area to the
second vertical line and adjust the TIMEIDIV switch so the
end of the timing area falls between the second and tenth
vertical lines.
Sweep Magnification
The sweep magnifier can be used to expand the display by a
factor of 10. The center division of the unmagnified display
is the portion visible on the crt in the magnified form (see
Figure 1-5).The equivalent length of the magnified sweep is
more than 100 divisions; any 10-division portion can be
viewed by adjusting the POSITION and FINE POSITION
controls to bring the desired portion intothe viewing area.
Fig. 1-5. Effect of sweep magnifier on crt display.
@
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Operating Instructions-7B85
When the MAGswitch is set to XI0 (OUT),the equivalent
magnified sweep rate can be determined by dividing the
TIMEIDIV setting by 10;the equivalent magnified sweep
rate
is displayedon the crt readout.
Variable Hold Off
The HOLD OFF control improvestriggering stability on re-
petitive complex waveforms by effectively changing the re-
petition rate of the horizontal sweep signal. The HOLD
OFF control should normally be set to its minimum setting.
When astable display cannot be obtained with the TRIG-
GERING LEVEL control, the HOLD OFF control can be
varied for an improved display. Ifastable display cannot be
obtained at any setting of the LEVEL and HOLD OFF
controls, check the TRIGGERING COLlPLlNG and
SOURCE switch settings.
Delay-Time Operation
A 7885 installed in the mainframe A horizontal compart-
ment can delay acompanion time-baseunit installed inthe
INTENSIFIED
PORTION
Fig.
1-6. (A) Delaying-sweepdisplay produced by 7885 in the A
horizontal compartment.
(B) Delayed-sweepdisplay produced by
companion time-baseunit in the
6 horizontal compartment.
B horizontal compartment. When operating the 7B85 ina
delaying mode (B DELAY MODE switch set to BSTARTS
AFTER DLYor BTRIGGERABLE AFTER DLY), an in-
tensified zone
is provided on the delaying sweep display
during the time that the companion time-baseunit runs (see
Figure 1-6).A delayed-sweeptrace
is provided by the com-
panion time-base unit, corresponding to the intensified
zone on the delaying trace, at the sweep rate set by the
TIMEIDIV switch of the companion time-base unit (see
Figure 1-6). The delay time between the triggering event
which starts the delaying-sweeptrace and the start of the
intensified zone (andcorrespondingdelayed sweep),
is de-
termined by the 7885 TIME/DIV switch and DELAY
TlME control. The amount of calibrated delay time is dis-
playedon the crt readout.
To view the delaying-sweeptrace (intensifieddisplay), set
the mainframe horizontal mode switch to A; to view the
correspondingdelayed-sweeptrace, set the mainframe hori-
zontal mode switch to B. To view the delaying trace (inten-
sified) and the corresponding delayed-sweeptrace on the
same display, set the mainframe horizontal mode switch to
alternate or chop.
Triggeringfor the delaying-sweeptrace is controlledby the
7885TRIGGERING controls. Triggering for the intensified
zone on the delaying-sweep trace and the corresponding
delayed-sweeptrace
is controlled by the triggering controls
of the companion time-base unit when the 7885 is in the B
TRIGGERABLE AFTER DLY mode.
Delay-time measurements must be made with the
B DELAY MODE switch set to B STARTS AFTER DLY.
When the B DELAY MODE switch is set to BTRIGGER-
ABLE AFTER DLY, the delayed sweep startswith the first
trigger pulse after the delay time shown on the crt readout.
Therefore, precisiontime measurementscannot be made in
this mode because the time delay
is only partially depen-
denton the DELAY TlMEcontrol.The crt readout displays
the greater-thansymbol
(>) precedingthe delay time when
operating in the BTRIGGERABLE AFTER DLYmode to
indicate that the delay time is uncalibrated. However, the
BTRIGGERABLE AFTER DLY mode is useful for trigger-
ing on waveforms with excessive jitter.
A Time Operation
The A TIME delaying mode provides the best means of
making differential time measurements. The 7885can de-
lay acompanion time-baseunit at
2 separate delay times.
At the end of the first delay time (determined bythe 7885
DELAY TlME control and TIMEIDIV switch) an intensi-
fied zone is provided on the delaying-sweeptrace. Further,
a separate delayed-sweeptrace corresponding to the first
intensified zone
is provided. Atthe end of the second delay
time (determined by the 7B85 TIMEIDIV switch, the DE-
LAY TIME, and
A TlME controls) a second intensified
zone and correspondingsecond delayed-sweeptrace are dis-
played (see Figure 1-7).The 7885 must be installed in the
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DN: cn=ArtekMedia, o=ArtekMedia.com, ou,
[email protected], c=US
Date: 2008.11.17 10:25:01 -06'00'

OperatingInstructions-7B85
DELAYING SWEEP
RATE
Dl
FFERENTIAL
MEASUREMENT DETERMINES IN-
TENSITY OF DE-
LAYED SWEEP
DELAYING
FIRST DELAYE
SWEEP TRACE
CORRESPONDING
TO FIRST INTEN- PROVIDES VERTI-
SlFlED ZONE CAL POSITIONING
OF DELAYED SWEEP
SECOND DELAYED TRACES WITH RE-
SWEEP TRACE COR- SPECT TO DELAY-
RESPONDING TO ING SWEEP TRACE
SECOND INTENSI-
FIED ZONE HORIZONTAL MODE
SWITCH SET TO
DIFFERENTIAL ALT OR CHOP FOR
A TlME OPERATION
CONTROLS TRIG-
GERING OF DELAY-
ING SWEEP TRACE
CONTROLS TRIG-
GERING OF INTEN-
SIFIED ZONES AND
DELAYED SWEEP
TRACES WHEN
B
DELAY MODE
SWITCH ISSET TO
B TRIGGERABLE
B DELAY MODE AFTER DLY
SWITCH SET TO
B STARTS AFTER
DLY FOR
A TIME DETERMINES
SWEEP RATE OF
INTENSIFIED
ZONES AND DE-
LAYED SWEEP
TRACES
DETERMINES THE
AMOUNT OF DELAY
OF THE DELAYING FERENTIAL MEASURE-
SWEEP TRACE TO THE MENT AND CORRES-
CAL POSITlONING SWEEP RATE OF
START OF THE FIRST PONDING DIFFEREN- OF
DELAYED SWEEP
INTENSIFIED ZONE TlAL TIME READOUT ~~!p'&.'p~~~~h~
TRACE
AND CORRESPONDING
FIRST DELAYED DELAYEDSWEEP
SWEEP TRACE TRACE
1960-31
Fig. 1-7. Typical A (Differential) Timeoperation.
REV. A, APR. 1976
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Operating Instructions-7B85
A horizontal compartment. The companion time-baseunit
must be installed in the B horizontal compartment. The
TRACE SEP control must be rotated counterclockwise out
of the switch detent position for
A TlME operation. The
sweep rate for the delaying-sweeptrace is determined by
the 7885 TIMEIDIV switch and the sweep rate of the in-
tensified zones and corresponding delayed-sweepdisplay is
determined by the sweep rate setting of the companion
time-base unit.
The differential time betweenthe start of the first intensi-
fied zone and the start of the second intensified zone is
displayed on the crt readout (see Figure 1-7).A
A symbol
precedingthe delay-time readout indicates a differential
measurement. The
> (greater than) symbol following the
A symbol indicatesthat the TIMEIDIV VARIABLE control
is activated or that the B DELAY MODE switch is set to
B TRIGGERABLE AFTER DLYand therefore the differ-
ential time is uncalibrated.
The TRACE SEP control vertically positions the second
delayed-sweeptrace with respect to the first delayed-sweep
trace. Vertical positioning of the delayed-sweeptraces with
respect tothe delaying-sweeptrace is provided by the verti-
cal separation control on the oscilloscope mainframe.
A TlME OPERATION IN A DUAL-BEAM OSCILLO-
SCOPE MAINFRAME. The 7B85
A TlME function is com-
patible with 7000-series dual-beam mainframes and
operation is basically the same as given for
A Time
Operation. The 7B85 must be installed in the A horizontal
compartment and the companion time-base unit must be
installed in the B horizontal compartment, as with conven-
tional
4 plug-incompartment mainframes. Set the horizon-
tal mode switch so that the 7B85 provides horizontal de-
flection for one beam and the companion time-base unit
provides horizontal deflection for the other beam. Apply
the input signal to the desired vertical plug-in unit and
select that unit for vertical deflection of both beams.
Operation of the
A TlME mode in dual-beammainframes
with adedicated vertical system differs slightly from con-
ventional dual-beam mainframes with vertical-mode
switches.The plug-in unit in the left vertical compartment
providesvertical deflection of beam 1 and the plug-in unit
in the right vertical compartment providesvertical deflec-
tion for beam
2. Therefore, the input signal must be applied
to the units in boththe left and right vertical compartments
for
A TlME operation.
Mainframe Operating Modes
The 7B85 can also be operated either as an independent
time base in any Tektronix 7700-, 7800-, and 7900-series
mainframes,or as a delayed-sweepunit (B DELAY MODE
switch set to INDEPENDENT) in those mainframesthat
have two horizontal compartments. A companion delaying
time-baseunit (e.g., another 7B85) is required for delayed-
sweep operation. Refer to Applications in this section for
additional information.
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Operating Instructions-7B85
APPLICATIONS
The 7B85 is designed primarily for use with acompanion time-base unit ina readout-equipped mainframe to make delayed-
sweep time-interval measurements.The 7B85 can also be used as an independent non-delayingtime base. The following
procedures provide instructions for making several delayed-sweeptime-interval measurementsusing the delay-time and A (dif-
ferential) time modes. These procedures provide enough detail toenable the operator to adapt them toother related time-
interval measurements. Contact your Tektronix Field Office or representativefor assistance inmaking measurements not
described in this manual.
DELAYED-SWEEPMEASUREWIENTS
Complex signals often consist of a number of individual
events of differing amplitudes. Since the trigger circuits are
sensitive only to changes in signal amplitude, astable dis-
play can normally be obtained only when the sweep is trig-
gered by the event(s) having the greatest amplitude.
However, this may not produce the desired display of a
lower-amplitude portion which follows the triggering event.
The delayed-sweepfeature providesameans of delaying the
start of the delayed sweep by aselected amount following
the event which triggers the sweep generator. Then, the part
of the waveform which contains the informationof interest
can be displayed at the delayed-sweep rate with a higher
apparent magnification than
is provided by the MAG
switch.
The delayed-sweepfeature can also be used to provide rapid
and accurate time-interval measurements from a triggering
event (i.e., the start of the delaying sweep) to a selected
point or betweentwo selected points on adisplayed wave-
form. See General Operating Information inthis section for
afurther discussion of delay-time operation.
Inthe delay-time mode, the delayed (B)sweep runs for a
selected interval after the delaying (A)sweep as indicated
by an intensified zone superimposed on the delaying (A)
sweep trace. The length of the intensified zone indicates the
time that the delayed sweep runs and is determined by the
delayed (B)sweep plug-inunit sweep rate (TIMEIDIVset-
ting).The time from the start of the delaying (A)sweep to
the start of the intensified zone (i.e., the start of the delay-
ed sweep)can be read directly on the crt readout.
Inthe A (differential)time mode, the delayed (B)sweep
runs for asecond selected interval indicated by asecond in-
tensified zone superimposed on the delaying (A)sweep
trace. The two intensified zones can be positioned with the
DELAY TIME and A TIME controls. The crt readout then
indicatesthe differential (A)time from the start of the first
to the start of the second intensified zones.
By selectingthe mainframe alternate or chopped horizontal
operation, the delaying (A)sweep and either the first delay-
ed (B)sweep interval (delay-time mode) or both delayed
(B)sweep intervals (Atime mode) can be displayed simul-
taneously. Since the delayed (B)sweep(s)can be displayed
at a higher magnification than is available with the MAG
switch, more precise selection of time intervals
is possible.
The following procedures provide instructions for making
several types of time-interval measurements in the delay-
time and A (differential)time modes.
Time-Interval Measurements (Delay-Time Mode)
Perform the following procedure to measure the time from
atriggering event (start of sweep) to any point on adis-
played waveform:
1. Install the 7B85 in the mainframeA horizontal compart-
ment and a companion time-baseunit inthe B horizontal
compartment.
2. Set the 7B85 controls as follows:
B DELAY MODE BSTARTS AFTER DLY
(buttonin)
MAG
XI (buttonin)
HOLDOFF MIN (fully counter-
clockwise)
TRACE SEP OFF (fully clockwise)
VARIABLE Calibrated (knobin)
TIMEIDIV
3. Connect the signal to be measured to the vertical unit
input.
4. Set the mainframe for the A horizontal mode to display
the 7B85, and the vertical mode to display the vertical unit.
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