Tektronix 321 A User manual

IV I A .IN J U A L
TYPE
OSCILLOSCOPE
Tektronix, Inc.
S.W. Millikan Way • P. O. Box 500 • Beaverton, Oregon 97005 • Phone 6 -0161 • Cables: Tektronix
070- 25 564

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Ail Tektronix instruments are warranted
against defective materials and workman
ship for one year. Tektronix transformers,
manufactured in our own plant, are war
ranted for the life of the instrument.
Any questions with respect to the war
ranty mentioned above should be taken up
with your Tektronix Field Engineer.
Tektronix repair and replacement-part
service is geared directly to the field, there
fore all requests for repairs and replace
ment parts should be directed to the Tek
tronix Field Office or Representative in your
area. This procedure will assure you the
fastest possible service. Please include the
instrument Type and Serial number with all
requests for parts or service.
Specifications and price change priv
ileges reserved.
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Copyright © 196 by Tektronix, Inc.,
;V Beaverton, Oregon. Printed in the United
States of America. All rights reserved.
Contents of this publication may not be re
produced in any form without permission
>■flif the copyright owner.
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Prelimin ry Instructions
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Operating Instructions
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Section 1
Section 2
Section 3
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Section 6
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Type 321 A
The Typo 32! A Oscilloscope

Type 321A
SECTION I
CHARACTERISTICS
Introduction
The Tektronix Type 321A is a high-performance, dc-to-6
me, transistorized oscilloscope. Its light weight, small size
and ability to operate from a variety of power sources make
it a versatile field and laboratory instrument. The oscillo
scope can operate from its internally-contained rechargeable
battery pack, an external dc source or from a 115/230-volt
50-800 cycle ac line. Regulated power supplies in the instru
ment, accurate calibration, and precise linearity assure exact
time and amplitude measurements despite normal voltage-
source and power-supply-load changes that occur under
actual operating conditions.
Operating temperature range derived from tests indicates
optimum performance and reliability on its self-contained
batteries from 0° to + 0° C at altitudes up to 15,000 feet.
Temperature range without bolteries when operating from an
external source is —-15* C to +55° C. Non-operating tem
perature range is —55° C to -75* C without batteries
and — 0* C to + 0° C with batteries at altitudes to
50.000 feet.
For the operator's convenience, a front-panel battery light
indicates when the internal batteries are low. If external dc
or ac operation is being used insteod of the batteries, the
light turns on if the external voltage source drops too low
for proper power supply regulation.
A -position power switch on the front panel permits
convenient selection of charging rate and/or power source.
Vertical Deflection System
Bandpass—Dc to at least 6 me (3-db down) using dc cou
pling; using ac coupling, low-frequency 3-db down point
is 2 cps typical from a 1-kc reference.
Sensitivity—0.01 v/div to 20v/div in 11 calibrated steps;
accuracy is within 3% of front-panel markings. Con
tinuously variable from 0.01 v/div to about 50 v/div
uncalibrated.
Input Impedance—35 pf nominal paralleled by 1 megohm
|r.trl%), 8.2 pf nominal paralleled by 10 megohms
(+:2%i when using the P6006 10X Probe.
Maximum Allowable Input Voltage Rating—600 volts com
bined dc and peak ac; 600 volts (not 1200 volts) peak-to-
peak ac.
Triggering
Type—Automatic, or amplitude-level selection using pre
set stability.
Mode—Ac-coupled or Dc-coupled.
Slope—Plus, from rising slope of triggering waveform, or
minus from negative slope of triggering waveform.
Source—Internal from vertical signal, or external from
triggering signal.
Signal Requirements—Internal: 0.2 major division vertical
deflection at 1 kc increasing to 1 major division at 6 me.
External: 1 volt peak-to-peak at 1 kc increasing to 3 volts
peak-to-peak at 6 me. Nominal input impedance: 5 pf
paralleled by 100 kilohms (±20%).
Sweep
Type—Miller Integrator.
Sweep Rates—0.5 /isec/div to 0.5sec/div in 19 calibrated
steps. Accurate 5X sweep magnifier extends calibrated
range to 0.1 psec/div. Calibrated sweep-rate accuracy
is ±-3%. Sweep lime adjustable between steps and to
>1.5sec/div uncalibrated.
External Horizontal Input
Bandpass—Dc to at least 1 me (3-db down).
Deflection Factor—1 v/dv drl0% with 5X magnifier on.
Input Impedance—30 pf typical paralleled by 100 kilohms
(± 5 % ).
Amplitude Calibrator
Square Wave—Frequency about 2 kc.
Amplitude—500 mv peak-to-peak. Also 0 mv peak-to-
peak internally coupled in CAL DIV position of VOLTS/
DIV switch. Peak-to-peak amplitude accuracy is r+3%.
Cathode-Ray Tube
Type—Special Tektronix-manufactured T3211. 3" flat-face,
post-deflection accelerator. Low heater power.
Accelerating Potential— kv.
Z-Axis Modulation—External terminal permits RC coupling
to ert grid.
Unblanking—Deflection unblanking.
Phosphor—Type P31 normally furnished; PI, P2, P7, and
PI 1 phosphors optional. Other phosphors furnished on
special order.
Graticule
Illumination—Variable edge lighting when operating from
ac line.
Display Area—Marked in 6-vertical and 10-horizontal y "
divisions.
Power Requirements
Source—Operates from 10 size D flashlight cells, or 10
size D rechargeable cells (approximately 3 hours using
2.5 ampere-hour cells,- approximately 5 hours using
1-1

Ch r cteristics — Type 321A
ampere-hour cells), or 11.5 to 35 volts dc (aircraft, outo,
boat, etc.), or 103.5 to 126.5 volts or 207 to 253 volts,
rms, 50 to 800 cycles, single-phase ac.
Power Consumption—Approximately 700 ma from internal
batteries or external dc source; 20 watts nominol at
115-volt ac line.
Temperature Protection—Thermal cutout switch interrupts
power if ambient temperature exceeds 131° F (55° C).
Built-in battery charger is standard equipment.
Environmental Capabilities
Vibration (operating)—0.025" peak-to-peak, 10 to 55 to
lOcps in 1 minute sweeps ( G's) for 15 minutes on
each axis. Three-minute vibration at resonance or
55cps on each axis.
Shock (operating)—20 G's, !/s sine, 11-msec duration.
Two shocks each direction along each of the three
major axis.- bottom, top, left side, right side, front
and rear. Total of 12 shocks.
Shock [non-operating)—60 G's, '/j sine, 11-msec dura
tion. One shock each direction along each of the three
major axis; total of 6 shocks.
Humidity |non-operating)-—Meets Mil-Std-202B, method
106A (except freezing and vibration) through 5 cycles
(120 hours).
Transit (non-operating)—Meets National Safe Transit test
when factory packaged. Vibration for one hour at
slightly greater than one G. Eighteen-inch drop in any
orientation.
Mechanical Specifications
Construction—Aluminum olloy chassis and cabinet.
Finish—Anodized panel, blue vinyl-finish cabinet.
Dimensions—S'/*" high, 53/," wide, 16" deep overall.
ACCESSORIES
Information on accessories for use with this instrument is
included at the rear of the mechanical parts list.
1-2

SECTION 2
PRELIMINARY INSTRUCTIONS
Power Requirements
The regulated power supplies in the Type 321A will operate
form 115-v or 230-v rms ac line, from an external dc source
(11.5 to 35 volts), or from a "battery pack” consisting of
either 10 size D flashlight cells or 10 size D rechargeable
cells.
Fuse Data
Use only the recommended fuses in the Type 321A Oscil
loscope. The upper fuse, F621 (see Fig. 2-1), is a 1.5-amp
3AG Fast-Bio; the lower fuse, F601, is a .25-amp 3AG Fast-
Blo. Neither fuse needs to be changed if the oscilloscope
is converted from one line voltage to the other (115 v and
230 v).
Fig. 2*1. Location of fuses and Charger switch (left-side view).
Ac Operation
Unless tagged otherwise, your instrument is connected at
the factory for operation at 103.5 to 126.5 volts, 50 to 800
cycles ac (115 volts nominal). However, provisions are made
for easy conversion to operate at 207 to 253 volts, 50 to
800 cycles (230 volts nominal). The power transformer T601
is provided with split input windings which are normally
connected in parallel for 115-volt operation, but which can
be connected in series for 230-volt operation.
The primary windings are marked 1, 2, 3, and . Terminals
1 and 3 are connected to one winding and terminals 2 and
are connected to the second winding. The ac input leads are
connected to terminals 1 and for both 115-volt and 230-
volt operation, so these connections do not have to be
changed when converting from one line voltage to the other.
When wired for 115-volt operation, terminals 1 and 2 are
joined by a bare bus wire, and terminals 3 and are simi
larly joined, as shown in Fig. 2-2|a). To convert to 230-
volt operation, remove the bare bus wires between these
terminals and substitute a single connecting wire between
terminals 2 and 3, as shown in Fig. 2-2(b).
To turn on the Type 321A when the power cord is con
nected to the oscilloscope power connector and to the ac
voltage source, set the POWER switch to EXT ON. To turn
off the oscilloscope, set the POWER switch to TRICKLE. The
TRICKLE position can be regarded as the normal "off" posi
tion for the instrument.
Fig. 2-2. (al Transformer connection for operation from 103.5-
126.5 volt ac line; <b) connections for operation from 207*253
volt ac line.
As long as the ac power cord is connected to the ac line,
power is being applied to the power transformer T601, c-
rectifier circuit, and graticule lights for all positions of the
POWER switch. Application of power to these circuit is re
quired to provide battery-charger operation for the internal
batteries; the graticule lights provide visual indication that
these circuits are on". Power to the battery charger itself is
controlled by a Charger switch (see Fig. 2-1). If the switch
2-1

Prelimin ry Instructions — Type 321A
is set to LOW or HIGH, the ac rectifier is connected to the
battery charger circuit which, in turn, provides charging cur
rent to the internal rechargeable batteries.
NOTE
If dry cells are used instead of rechargeable bat
teries, then the Charger switch must be set to DRY
CELLS to disconnect the charger circuit. For further
information about battery operation, refer to the
topics tilled “ Battery Operation” and "Battery
Charger" appearing in this section of the manual.
If the Type 321A is being operated exclusively from the
ac line and the internal batteries are removed, the Charger
switch can remain in the DRY CELLS position to disconnect
the charger circuit. If you prefer to completely turn off
all power to the Type 321 A, set the POWER switch to
TRICKLE and either disconnect the power cord from the
ac line or turn off the power at a wall switch (or equiv
alent).
Battery Operation
Operation from the internal battery source can be accom
plished by using:
1. Ten size D flashlight cells (approximately '/j-hour con
tinuous operation, more with intermittent operation), or
2. Ten size D Alkaline cells such as Eveready E95, Burgess
AL-2, or Mallory MN-1300 (about 2'/3 hours continuous
operation), or
3. Ten size D nickel-cadmium rechargeable cells (up to
about 5 hours continuous operation, depending on the
type used).
The nickel-cadmium cells are the most practical type where
considerable battery operation is planned.
To install the cells, first open the battery cover os illus
trated in Fig. 2-3. Next, install the batteries by following
the procedure given in Fig. 2- .
CAUTION
Be sure to observe cell polarity indicated on the
battery cover.
To turn on the Type 321A when operating from the internal
batteries, set the POWER switch to BATT ON. To turn off the
oscilloscope, set the POWER switch to one of the OFF posi
tions—FULL or TRICKLE. These OFF positions disconnect
the batteries from the oscilloscope load (10-volt regulated
supply) so there is no battery drain. To charge the recharge
able batteries, refer to the next topic titled “ Battery Charger".
• Vi*
loosen rhumb screw to unlock
cover, then pull cover forward »o
rttnovt-
2-2
Fifl. 2-3. Rem*>vln9 the battery cover from the Type 321A Oscilloscope.

Prelimin ry Instructions — Type 321A
——
P W i l
Terminal.
External
2. Install five cells in each side 3. Insert battery spacer,
of the battery holder. Be sure i
to observe cell polarity as In-
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Fig. 2- . Procedure for installing the batteries.
Battery Charger
As mentioned previously, the battery charger is connected
to the internal batteries as long as the ac power cord is
connected to an ac power source and the Charger switch
(see Fig. 2-1) is set to HIGH or LOW. No charging occurs if
the Charger switch is set to DRY CELLS.
Table 2-1 summarizes the charging currents that can be
obtained by using various line voltages in combination with
various settings of the POWER and Charger switches. The
table shows the Type 321A wired for 115-volt nominal line
operation, If the oscilloscope is wired for 230-volt nominal
line operation, the charging currents will still be the same
but the ac line voltages will be twice the amount shown in
the table.
Use Table 2-1 as an aid in determining the proper posi
tion for the POWER and Charger switches for the particular
brand or type of rechargeable batteries being used in the
Type 321 A. After setting the switches to their proper posi
tion, the line voltage can then be set to the charging rate
recommended by the manufacturer of the cells. An auto
transformer having a rating of at least I ampere and
equipped with an rms-reading ac voltmeter can be used to
set the line voltage.
When using rechargeable batteries, sixteen hours of
charging at the full rated charging current recommended
by the manufacturers should be adequate to fully charge
the batteries. Excess charging may damage the batteries.
One method for determining charge conditions of the bot-
teries is to set the POWER switch to BATT ON and then
measure the voltage across the battery terminals (see Pig,
2- ). A reading higher than 13 volts indicates that the
batteries are fully charged. A reading lower than 13 volts
indicates that more charging time is required.
As mentioned previously, if dry cells are installed in the
battery holder and the Type 321A is being operated from
the ac line, the Charger switch must be set to the DRY CELLS
position. This position disconnects the charging circuit from
the batteries.
TABLE 2-1
Ch rging Currents
POWER*
Switch
Position
Charge^
Switch | Aproximate Charging
Current in Ma
Position 103.5 v 109 v 115 v 121 v 126.5 v
EXT ON LOW 20 2 27 31 33
HIGH 22 26 30 33 35
TRICKLE LOW 31 3 38 1
HIGH 3 37 1 8
FULL LOW 160 Li80 200 220 230
HIGH 290 I 320 360 380 10
•The BATT ON position is not included in the table because the
Type 321A should not be operated from the oc line and the
batteries ot the same time. Reoson; Battery drain oxceods charg
ing rote.
2-3

Prelimin ry Instructions — Type 321A
Dc Operation
Operation from an external dc source is acomplished by
connecting the special pigtail-type dc power cord in the
proper manner. For 11.5- to 20-volt operation, the black
1 -1 and white (—) leads are connected to the voltage
source.: for 20- to 35-volt operation, the green H-| and white
{—) leads are connected to the voltoge source. When the
connections to the external dc voltage source are properly
made, the external dc source is floating with respect to the
Type 321A chassis. Up to 600 volts difference is permissi
ble, if necessary.
To turn on the Type 321 A, set the POWER switch to EXT
ON. To turn off the oscilloscope, set the POWER switch to
one of the OFF positions—TRICKLE or FULL.
When operating from the external dc source, the ac line
cord should be disconnected. That is, only one of the exter
nal sources should be used rather than both at the same time.
NOTE
The internal battery charger circuit is disconnected
during external dc operation. Therefore, external
batteries (if used as the dc source) cannot be
charged by connecting the line cord to the ac line.
Also, an external dc source cannot be used to
charge the internal batteries since the POWER
switch does not electrically connect the two
sources together.
LOW BATTERIES Light
The LOW BATTERIES light turns on when the following
conditions exist:
1. The POWER switch is set to BATT ON and the internal
batteries drop to 11.5 v (di0.2 v) or lower.
2. The POWER switch is set to EXT ON and the external
source voltage is low enough to cause the Type 321A un
regulated voltoge to drop to about ll.S v or lower.
2-

SECTION 3
OPERATING INSTRUCTIONS
General Information
The Type 321A Oscilloscope is an extremely versatile in
strument, adaptable to a great number of applications. How
ever, to make full use of the instrument, it is necessary that
you understand completely the operation of each front-panel
control. This portion of the manual is intended to provide
you with the basic information you require. If you are
familiar with other Tektronix oscilloscopes, you should have
very little difficulty in understanding the operation of the
Type 321 A. The function of many controls is the same as
the function of corresponding controls on other Tektronix
instruments. A front-panel view of the Type 321A is shown
in Fig. 3-1.
Intensity Control
The INTENSITY control is used to adjust the trace bright
ness. This permits adjustment of trace intensity to suit the
ambient light conditions and changes in intensity caused
by changes in the sweep triggering rate (sweep duty cycle).
Clockwise rotation increases the intensity and counterclock
wise rotation decreases the intensity.
Focus and Astigmatism Controls
The FOCUS and ASTIGMATISM controls operate in con
junction with each other to allow you to obtain a sharp,
clearly defined spot or trace. To adjust these controls:
1. Adjust the INTENSITY control for the most pleasing level.
2. Set the ASTIGMATISM control to midscale.
3. Adjust the FOCUS control for sharpest detail.
. Adjust the ASTIGMATISM control as necessary for best
overall focus.
Graticule Illumination Control
The graticule used with the Type 321A is accurately
marked with 10 horizontal and 6 vertical divisions, with 0.2-
division markers on the centerlines. These graticule markings
allow you to obtain time and voltage measurements from
the oscilloscope screen.
Graticule illumination is adjusted by the SCALE ILIUM
control, located just to the right of the oscilloscope screen.
Rotating the control clockwise increases the brightness of the
graticule markings and counterclockwise rotation decreases
the brightness.
NOTE
The graticule is illuminated only when operating
from an ac line. This permits longer operation
when on batteries.
Positioning Controls
Two controls are used with the Type 321A Oscilloscope
to position the trace or spot on the screen.
The HORIZONTAL POSITION control moves the trace to
the right when it is rotated clockwise and to the left when it
is rotated counterclockwise. This control has o positioning
range of approximately 15 divisions with the sweep magnifier
off, and approximately 75 divisions with the sweep magnifier
on.
The HORIZONTAL POSITION control is a combination
coarse/vernier type of control. Built-in blacklash between
its two sections permits 30° of vernier adjustment for a given
coarse setting. If a 30° range is exceeded, the coarse ad
justment takes over to provide fast positioning of the trace.
The VERTICAL POSITION control has sufficient range to
position the trace completely off the top or bottom of the
screen, or to any intermediate point. The troce moves up
when the control is rotated clockwise and down with the
counterclockwise rotation.
Intensity Modulation
The crt display of the Type 321A Oscilloscope can be in
tensity modulated by an external signal to display additional
information. This is accomplished by disconnecting the
grounding bar from the CRT GRID connector at the rear of
the instrument and connecting the external signal to this
terminal. A negotive signal of approximately 30 volts peak
is required to cut off the beam from maximum intensify, less
with lower intensity levels. Negative-going signals as low as
5 volts peak will accomplish intensity modulation.
HORIZONTAL DEFLECTION SYSTEM
Horizontal Sweep
The usual oscilloscope display is a graphical presentation
of instantaneous voltage versus time. Voltage is represented
by vertical deflection of the trace and time is represented
by horizontal deflection. To obtain a useful display, the spot
formed by the electron beam is deflected horizontally at a
known rate, so that any horizontal distance on the screen
represents a definite known period of time. The trace formed
by the deflection of the spot across the screen is known as
the horizontal sweep. Since the horizontal deflection of the
spot bears a definite relationship to time, and provides the
means for making time measurements from the screen, the
horizontal sweep is also known as the time base. (See Fig.
3-2).
The rate at which the spot is deflected across the screen
is accurately controlled by the setting of the TIME/DIV con
trol. The setting of the TIME/DIV control determines the
sweep rate, and thus the number of cycles displayed on the
crt screen. The control is set to display the portion of the
waveform you wish to observe.
3-1

Oper ting Instructions — Type 321A
CRT CONTROLS
ASTIGMATISM— Used in conjunc
tion with FOCUS to obtain overall
focus.
SCALE ILIUM— Adjusts brightness
of graticule markings (when oper-
from AC lin e).
FOCUS — Controls sharpness of
spot or trace. INTENSITY— Controls brightness of
HORIZONTAL CONTROLS
DC BAl— Potentiometer for sotting
dc balance of Vortical Amplifier.
VERTICAL CONTROLS
TRIGGERING CONTROLS
INPUT —• Terminal for accepting
waveforms to be displayed on crt.
CAL OUT 500 MV— Terminal pro
vides 500-mv square wave for
compensating probe.
LEVEL— Selects point on triggering
signal at which sweep is triggered.
SLOPE— Determines whether sweep
is triggered on -f- or — slope of
triggering signal.
AC-OC— Selects AC or DC coupling
for triggering signal.
INT-EXT— Selects either internal or
external triggering signal.
STABILITY— Potentiometer for set
ting dc level of sweep generator.
VERTICAL POSITION — Positions
trace vertically.
AC-OC-GND— Selects either AC or
DC input coupling. The GND posi
tion connects the Vertical Amplifier
to ground but does not ground
the input signal.
VOLTS/DIV and VARIABLE — Se
lects vertical deflection factor and
calibrator signal.
HORIZONTAL POSITION— Coarse-
vemier type of control that posi
tions trace horiiontally.
POWER— Switch turns regulated
10-volt power on and off. Also,
selects charging rate.
TIME/DIV and VARIABLE— Selects
sweep rate and extemol horizontal
Input.
EXT HORIZ INPUT— Terminal for
accepting external horizontal sig
nal.
INPUT— Terminal for accepting ex.
ternal triggering signal.
3-2
Fig. 3-1. Functions of the Typo 321A Oscilloscope front-panel controls.

Oper ting Instructions — Type 321A
Voltage
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Time
Fig. 3-2. The oscilloscope plots instantaneous voltage versus time,
thereby serving both as a voltmeter and a timer.
The Time Base has 19 accurately calibrated sweep rates
ranging from .5 jxsec/div to .5sec/div. These calibrated
sweep rates are obtained when the VARIABLE (TIME/DIV)
control is fully clockwise in the CALIB position. The TIME/
DIV switch selects the calibrated sweep rates and can be
rotated 360° since there are no mechanical stops. The VARI
ABLE control permits you to vary the sweep rote continuously
between .5/»sec/div and approximately 1.5sec/div. All
sweep rates obtained with the VARIABLE control in any
position other than fully clockwise are uncalibrated.
Sweep Magnifier
The sweep magnifier allows you to expand any two-
division portion of the displayed waveform to the full ten-
division width of the graticule. This is accomplished by first
using the HORIZONTAL POSITION control to move the por
tion of the display you wish to expand to the center of the
graticule, then placing the 5X MAG switch in the “on" posi
tion (pull out the red VARIABLE TIME/DIV knob; see Fig.
3-3). Any portion of the display magnified by the horizontal
sweep can then be observed by rotating the HORIZONTAL
POSITION control.
In magnified sweep operation, the sweep rate indicated
by the position of the TIME/DIV switch must be divided by
5 to obtain the actual time required for the spot to move
one division. For example, if the TIME/DIV switch is set to
5 MILLI SEC, the actual time per division is 5 milliseconds
divided by 5, or 1 millisecond per division. The actual time-
per-division must be used for all time measurements.
External Horizontal Input
For special applications you can deflect the trace hori
zontally with some externally derived waveform rather than
by means of the internal sweep sawtooth. This allows you
to use the oscilloscope to plot one function versus onother.
To use the external horizontal input, connect the externally
derived waveform to the EXT HORIZ INPUT connector and
place the TIME/DIV switch in the EXT position. The hori
zontal deflection factor is approximately 1 volt/division with
the 5 X MAG on.
Fig. 3-3. Operation of the swoop magnifier.
Sweep Triggering
The oscilloscope display is formed by the repetitive sweep
of the spot across the oscilloscope screen. If the sweeps are
allowed to occur at random, or a rate unrelated to the input
waveform, the displayed waveform will be traced out at a
different point on the screen with each sweep. This will
either cause the waveform to drift across the screen or to be
indistinguishable.
In most cases it is desirable for repetitive waveforms to
appear stationary on the oscilloscope screen so that the
characteristics of the waveform can be examined in detail.
As a necessary condition for this type of display, the start
of the sweep must bear a definite, fixed-time relationship to
the observed waveform. This means that each sweep must
start at the same time, relative to some point on the observed
waveform. In the Type 321 A, this is accomplished by start
ing or triggering the sweep with the displayed waveform, or
with another waveform bearing a definite time relationship
to the displayed waveform.
The waveform used to start the horizontal sweep is called
a "triggering signal" (whether it is the waveform being ob
served, or some other waveform). The following instructions
tell you how to select the triggering signal source.
Selecting the Triggering Source
In preparing the Type 321A Oscilloscope for triggered
operation of the sweep, it is first necessary to select the
triggering signal source which will provide the best display
for the particular application. The sweep can be triggered
by the displayed waveform, or by on externally derived
waveform. This selection is made by the setting of the INT
EXT switch (see Fig. 3- ). Each type of triggering has certain
advantages for some applications.
Triggering from the disployed waveform is the method
most commonly used. The disployed waveform is selected
when the INT-EXT switch is in the INT position. Internal trig-
3-3

Oper ting Instructions — Type 321A
gering is convenient since no external triggering connections
are required. Satisfactory results are obtained in most appli
cations.
To trigger the sweep from some external waveform, con
nect the triggering waveform to the (TRIGGERING) INPUT
connector and place the INT-EXT switch in the EXT position.
(External triggering provides definite advantages over in
ternal triggering in certain cases.) With external triggering,
the triggering signal usually remains constant in amplitude
and shape. It is thereby possible to observe the shaping and
amplification of a signal in an external circuit without reset
ting the oscilloscope triggering controls for each observation.
Also, time and phase relationships between the waveforms at
different points in the circuit can be seen. If, for example,
the external triggering signol is derived from the waveform
at the input to a circuit, the time relationship and phase of
the waveforms at each point in the circuit ore compared to
the input signol by the display presented on the oscilloscope
screen.
Selecting the Triggering Slope
The horizontal sweep can be triggered on either the rising
or falling portion of the triggering waveform. When the
SLOPE switch is in the -+• position, the sweep is triggered
on the rising portion of the triggering waveform; when the
SLOPE switch is in the — position, the sweep is triggered on
the falling portion of the waveform (see Fig. 3-5).
In many applications the triggering slope is not important
since triggering on either slope will provide a display suitable
to the application.
Selecting the Triggering Mode
Automatic Mode
Automatic triggering is obtained by rotating the (TRIG
GERING) LEVEL control fully counterclockwise to the AUTO
position.
This mode allows triggering at the average voltage point
of the applied waveform. Also, the sweep runs at approxi
mately a 50-cycle rote when no triggering signals are ap
plied; this produces a reference trace or baseline on the
screen. Automatic triggering can be used with both internal
and external triggering signals, but for most waveforms
it is useful only for triggering at frequencies above 50 cycles.
Automatic triggering saves considerable time in observing
a series of waveforms since it is not necessary to reset the
triggering level for each observation. For this reason it is
the mode that is normally used. Other modes are generally
used only for special applications, or where stable trigger
ing is not attainable in the automatic mode,
3-
Fig. 3- The triggering signal Is selected from two possible sources with the INT-EXT switch.

Oper ting Instructions — Type 321A
LEVEL
SLOPE
+
►
Sweep Triggers
On -f- Slope
SLOPE
+
Swoop Triggers
On — Slope
►
Waveforms obtained with the trig*
gering level control set In the
— region.
SLOPE
Sweep Triggers
On •— Slope
Waveforms obtained with the trig
gering level control set in the
- region.
3-5
Fig. 3*5. Effects on the oscilloscope display produced by + and — settings of the SLOPE ond LEVEL controls.

Oper ting Instructions — Type 321A
Ac Mode
Ac-mode triggering is obtained by setting the AC-DC
switch to the AC position. This mode provides stable trig
gering on virtually all types of waveforms. As a general
rule, however, the ac mode is unsatisfactory for triggering
with low amplitude waveforms at frequencies below approxi
mately 15 cycles. This figure will vary depending upon the
amplitude and shape of the triggering waveform and should
not therefore be set as an absolute standard. Triggering at
frequencies below 15 cycles can be accomplished when
higher amplitude triggering signals are used.
In the ac mode, the triggering point depends on the
average voltage level of the triggering signals. If the trig
gering signals occur at random, the average voltage level
will vary causing the triggering point to vary also. This shift
of the triggering point may be enough so that it is impossible
to maintain a stable display. In such cases you should use
the dc mode,
Dc Mode
Dc mode triggering is obtained by setting the AC-DC
switch to the DC position. This mode of triggering is par
ticularly useful in triggering from waveforms which are not
adaptable to the ac mode, such as random pulse trains or
very low-frequency waveforms. Random pulse trains pose
a special problem in the ac mode since the random occur
rence of the input waveforms causes the average voltage
level to shift. This in turn may cause the triggering level to
shift to an unstable point. This problem is not encountered
in the dc mode since the triggering point is determined only
by instantaneous voltages.
In the dc mode, when the triggering signal is obtained
from the Vertical Amplifier, varying the VERTICAL POSITION
control will change the triggering point. For this reason,
you may find it necessary to readjust the LEVEL control when
you change the vertical position of the trace. To eliminate
this effect, you can use the ac mode provided the triggering
signal is otherwise suitable for this mode of operation. In
the dc mode, the dc level of the external triggering signals
will olso effect the triggering point. Generally, when the
triggering signal is smoll compared to its dc level, the oc
mode should be used.
How to Set the Triggering Level
In the ac and dc triggering modes, the LEVEL control
determines the voltage level on the triggering waveform at
which the sweep is triggered. Using this control, the sweep
can be continuously triggered at any point on the waveform
so long as the slope of the waveform is great enough to
provide stoble triggering. In the dc mode, the sweep cannot
be triggered with any degree of stability at the top of a
square wove, for example, because the time that the voltage
remains constant is comparatively long. As a result, the
sweep triggers at random points along the fop of the square
wave, producing considerable trace jitter.
You can use the same metnod to set the LEVEL control for
either the ac or dc mode. After selecting the triggering
slope, rotate the LEVEL control fully counterclockwise to the
AUTO position. Then rotate the LEVEL control clockwise
until the sweep no longer triggers. Continue to rotate the
control in the clockwise direction until the sweep again trig
gers and a stable display is obtained. Further rotation of the
control in the clockwise direction causes the sweep to trigger
at more positive points on the triggering waveform. In the
fully clockwise direction the trace will free run (Fig. 3-5).
FREE-RUNNING OPERATION
With the Type 321 A, you can get o periodic, free-running
sweep, independent of any external triggering or synchroniz
ing signal, by rotating the LEVEL control fully clockwise to
the FREE RUN position. This permits you to observe the trace
without an input signal. This trace con then be used to posi
tion the sweep or to establish a voltage reference line. The
difference between the traces produced in the AUTO position
and the FREE RUN position is the repetition rate. The repeti
tion rate in the FREE RUN position is dependent upon the
setting of the timing switch. The repetition rate in the AUTO
position is fixed at approximately 50 cycles. At the faster
sweep rates, the trace in the AUTO position will appear to
be dim. In the FREE RUN position the trace intensity remains
essentially constant for all sweep rates.
VERTICAL DEFLECTION SYSTEM
Input Coupling
Input signals to the Vertical Amplifier can be either ac- or
dc-coupled by placing the AC-DC-GND switch in the ap
propriate AC or DC position. Dc coupling applies both the
ac and dc components of the input signal to the vertical
amplifier circuit. This permits measurement of the dc voltage
level as well as the amplitude of the ac component. It is
sometimes neither necessary nor desirable to display the dc
component, however, and in such cases as coupling should
be used. This is accomplished by setting the AC-DC-GND
switch to AC. With ac coupling, a capacitor is placed in
series with the input connector to block the dc component
while allowing the ac component to be displayed.
Placing the AC-DC-GND switch to the GND position
grounds the input circuit of the vertical amplifier to provide
a dc zero reference. In this position the switch internally dis
connects, but does not ground, the applied signal to the
input connector. Thus, the GND position eliminates the usual
need for externally grounding the (Vertical Amplifier) INPUT
connector of the Type 321A or the probe tip to establish a
ground reference.
Deflection Factor
The elecfricol waveform to be observed is applied to the
(Vertical Amplifier) INPUT connector. The waveform is then
applied through the vertical-deflection system to cause the
spot to be deflected vertically to trace out the waveform on
the screen of the crt. The VOLTS/DIV switch controls the
vertical deflection factor in accurately calibrated steps. The
VARIABLE control provides uncalibrated variable deflection
factors between the fixed steps of the VOLTS/DIV switch.
The VARIABLE control has 360° rotation range and a detent
position when the control is set to CALIB.
3-6

Oper ting Instructions — Type 321A
NOTE
To make the deflection factor equal to that indi
cated by the VOLTS/DIV switch, set the VARIABLE
control to the CALIB detent position.
Dc Balance Adjustment
The need for adjustment of the DC BAL control is indi
cated by o vertical shift in the position of the trace as the
VARIABLE (VOLTS/DIV| control is rotated. This adjustment
should be made as follows:
1. Set the AC-DC-GND switch to GND.
2. Set the oscilloscope controls for a free-running trace.
3. Rotate the VARIABLE (VOLTS/DIV) control back and forth,
and adjust the DC BAL control simultaneously until the
trace position is no longer affected by rotation of the
VARIABLE control.
Input Signal Connections
Certain precautions must be observed when you are con
necting the oscilloscope to an input signal source. This is
to insure that accurate information is obtained from the
oscilloscope display. This is particularly true when you
are observing low-level signals, or waveforms containing
high- or extremely low-frequency components. For applica
tions where you are observing low-level signals, shielded
cables should be used whenever possible, with the shield
connected to the chassis of both the oscilloscope and the
signal source. Unshielded input leads are generally unsatis
factory due to their tendency to pick up story signals which
produce erroneous oscilloscope displays. Regardless of the
type of input used, the leads should be kept as short as
possible.
Distortion of the input waveform may result if:
1. Very low-frequency input signals are ac-coupled to the
oscilloscope.
2. High-frequency waveforms are not properly terminated.
3. The input waveform contains high-frequency components
which exceed the bandpass of the oscilloscope.
You must be aware of the limitations of the instrument.
In analyzing the displayed waveform, you must consider
the loading effect of the oscilloscope on the input signal
source. In most cases this loading effect is negligible; how
ever, in some applications loading caused by the oscilloscope
may materially alter the results obtained. In such cases you
may wish to reduce the amount of loading to a negligible
amount through the use of o probe.
Use of Probes
Occasionally connecting the input of an oscilloscope to
a signal source loads the source sufficiently to adversely
affect both the operation of the source and the waveform
displayed on the oscilloscope. In such cases an attenuator
probe may be used to decrease both the capacitive and resis
tive loading caused by the oscilloscope to a negligible value.
In addition to providing isolation of the oscilloscope from
the signal source, an attenuator probe also decreases the
amplitude of the displayed waveform by the attenuotion
factor of the probe. Use of the probe allows you to increase
the vertical-deflection factors of the oscilloscope to observe
large-amplitude signals beyond the normal limits of the
oscilloscope. Signal amplitudes, however, must be limited to
the maximum allowable value of the probe used. When
making amplitude measurements with an attenuator probe,
be sure to multiply the observed amplitude by the attenua
tion of the probe.
If the waveform being displayed has rapidly rising or
falling voltages, it is generally necessary to clip the probe
ground lead to the chassis of the equipment being tested.
Select a ground point near the point of measurement, as
shown in Fig. 3-6.
Prob* tip conn*cl«d to tignal tourc*
Probo ground load conn«l«d to chattlt
Equipmont being checked
Fig. 3-6. Connecting a probe to the input signal source.
Before using a probe you must check (and adjust if neces
sary) the compensation of the probe to prevent distortion of
the applied waveform. The probe is compensated by adjust
ing the control located in the body of the probe. Adjustment
of the probe compensates for variations in input capacitance
from one instrument to another. To insure the accuracy of
pulse and transient measurements, this adjustment should be
checked frequently.
To adjust the probe compensation, set the VOLTS/DIV con
trol to the .01 position and the LEVEL control to the AUTO
position. Set the SLOPE switch to + and the INT-EXT switch
to INT. Connect the probe tip to the CAL OUT 500 MV con
nector. Set the TIME/DIV switch to .5 MILL! SEC and adjust
the probe to obtain flat tops on the displayed square wave
form (see Fig. 3-7.)
3-7

Oper ting Instructions — Type 321A
Voltage Measurements
The Type 321 A Oscilloscope can be used to measure the
voltage of the input waveform by using the calibrated ver
tical-deflection factors of the oscilloscope. The method
used for all voltage measurements is basically the same
although the actual techniques vary somewhat depending on
the types of voltage measurements, i.e., ac-componenf volt
age measurements, or instantaneous voltage measurements
w'th respect to some reference potential. Many waveforms
contain both ac and dc voltage components, and it is often
necessary to measure one or both of these components.
When making voltage measurements, you should display
the waveform over as large a vertical portion of the screen
as possible for maximum accuracy. Also, it is important that
you do nor include the width of the trace in your measure
ments. You should consistently make all measurements from
one side of the trace. If the bottom side of the trace is used
for one reading, it should be used for all succeeding read
ings. The VARIABLE (VOLTS/DIV) control must be In the
CALIB detent position.
Ac Component Voltage Measurements
To measure the ac component of a woveform, the AC-DC-
GND switch should be set to the AC position. In this position
only the ac components of the input waveform are displayed
on the oscilloscope screen. However, v/hen the ac component
of the input waveform is very low in frequency, it will be
necessary for you to make voltage measurements with the
AC-DC-GND switch in the DC position.
To moke a peak-to-peak voltage measurement on the ac
component of a waveform, perform the following steps |see
% 3-8|.
1. With the aid of the graticule, measure the vertical dis
tance in divisions from the positive peak to the negative
peak,
2. Multiply the setting of the VOLTS/DIV control by the dis
tance measured to obtain the indicated voltage.
3. Multiply the indicated voltage by the attenuation factor
of the probe you are using to obtain the true peak-to-peak
voltage.
As an example of this method, assume that using the
P6006 Probe and a deflection factor of 1 volt per division,
you measure a vertical distance between peaks of divisions.
In this case, then, divisions multiplied by 1 volt per divi
sion gives you an indicated voltage of volts peak-to-peak.
The indicated voltage multiplied by the probe's attenuation
factor of 10 then gives you the true peak-to-peak amplitude
of 0 volts.
When sinusoidal waveforms ore measured, the peak-to-
peak voltage obtained can be converted to peak, rms, or
average voltage through use of standard conversion factors.
Instantaneous Voltage Measurements
The method used to measure instantaneous voltages is
virtually identical to the method described previously for
the measurement of the ac components of a waveform. How
ever, for instantaneous voltage measurements the AC-DC-
GND switch must be placed in the DC position. Also, since
instantaneous voltages are measured with respect to some
potential [usually ground), a reference line must be
established on the oscilloscope screen which corresponds to
that potential. If, for example, voltage measurements are to
be made with respect to -f-100 volts, the reference line would
correspond to -f-100 volts. In the following procedure a
method is presented for establishing this reference line at
ground, since measurements with respect to ground are the
Incorrect Adjusted Correctly Incorrect
P6006 Probe— Hold probe barrel and
loosen locking sleeve severol turns. Hold
probe base while odujsting probe barrel
for flat-top square waves. Hold probe
barrel and corefully tighten locking
s l e e v e .
___________________
i-.iir.k k k .
3-8
Fig. 3-7. The probe it adjusted to obtain an undistorod presentation of the calibrator squarewavo.

Oper ting Instructions — Type 321A
Fig. 3-8. Measuring the peak-to-peak ac voltage of an applied waveform.
most common type. The same general method may be used
to measure voltage with respect to any other potential, how
ever, so long as that potential is used to establish the ref
erence line.
To obtain an intonfaneous voltage measurement with res
pect to ground, or some other voltage, perform the following
steps (see Fig. 3-9).
1. To establish a ground reference line, set the AC-DC-
GND switch to GND. Or, to establish a reference line
which represents a voltage other than ground, touch the
probe tip to the voltage and leove the AC-DC-GND
switch at DC. Then adjust the oscilloscope controls to
obtain a free-running sweep. Vertically position the trace
to a convenient point on the oscilloscope screen. This
point will depend on the polarity ond amplitude of the in
put signal, but should always be chosen so that the trace
lies along one of the major divisions of the graticule.
The graticule division corresponding to the position of
the trace is the volfoge reference line and all voltage
measurements must be made with respect to this line.
(Do not adjust the VERTICAL POSITION control after the
reference line has been established.)
2. If ground reference was established, set the AC-DC-GND
switch to DC; if a reference line other thon ground was
established, remove the probe tip from this voltage and
connect it to the signal source. Adjust the LEVEL control
for a stable display.
Pre-established
reference line
(usually ground)
Instantaneous
__ Voltage With
— Respect To
Reference Voltage
Probe Attenuation Factor Vertical Deflection
From Reference Lino
3-9
Fig. 3-9. Measuring the instantaneous voltage with respect to ground (or some other reference voltoge).

Oper ting Instructions — Type 321A
3. Measure the verticol distance in divisions from the desired
point on the waveform to the voltage reference line.
. Multiply the sotting of the VOLTS/DIV control by the dis
tance measured to obtain the indicated voltage.
5. Multiply the indicated voltage by the attenuation factor
of the probe you are using to obtain the actual voltage
with respect to ground (or other reference voltage).
As on example of this method, assume you are using the
P6006 Probe and a deflection factor of 0.2 volt per division.
After setting the voltage reference line at the second from
bottom division of the graticule, you measure a distance of
3 divisions to the point you wish to check. In this case,
3 divisions multiplied by 0.2 volt per division gives you an
indicated 0.6 volt. Since the voltage point is above the
voltage reference line the polarity is indicated to be posi
tive. The indica'ed voltage multiplied by the probe attenua
tion factor of 10 then gives you the actual voltage of +6
volts.
Time Measurements
The calibrated sweep of the Type 321A Oscilloscope causes
any horizontal distance on the screen to represent a definite
known interval of time. Using this feature you can accurately
measure the time lapse between two events displayed on
the oscilloscope screen. One method which produces suf
ficient accuracy for most applications is as follows (see
Fig. 3-10).
1. Measure the horizontal distance between the two dis
played events whose time interval you wish to find.
2. Multiply the distance measured by the setting of the
TIME/DIV control to obtain the opparent time interval.
(The VARIABLE TIME/DIV control must in the CALIB posi
tion.)
NOTE
Divide the apparent time interval by 5 if the mag
nifier is on.
3-10
Fig. 3-10. Measuring the inlervol between events displayed on the oscilloscope screen.