Tektronix 545A Instruction Manual page 14

Operating
Instructions
—
Type 545A
TIME BASE
A TRIGGERING MODE
switch
to
AUTO,
and
the
TIME BASE
A TRIGGER
SLOPE
switch
to
-PINT. Turn up
the intensity
until
the trace
is
visible
and
connect
the
probe
tip to
the
CAL
OUT
connector.
Set the
AMPLITUDE
CALI-
BRATOR
switch
for
2 centimeters of
displayed
signal. Set
the
TIME BASE
A
TIME/CM
switch to display
approximately
3 or 4
cycles of the Calibrator
waveform and
adjust the
probe compensation
control
to
obtain
flat
tops
on
the
dis-
played
Calibrator square-waves
(see
Figure
2-3).
First
unlock
the
Locking
Sleeve by
turning
it
counter-
clockwise.
The probe
is
then compensated by
rotating the
probe body
while watching
the oscilloscope display
for the
desired
waveform.
When
compensation
is
completed,
care-
fully turn
the Locking Sleeve clockwise
to lock
it
without
disturbing the adjustment
of the probe.
Horizontal
Sweep
The
usual oscilloscope display
is
a graphical presentation
of instantaneous voltage versus
time.
Voltage
information
is
presented by
vertical deflection of the trace
and
time
information
is
presented
by
horizontal
deflection.
To obtain
a useful display,
it is
necessary
for
the spot
formed by
the
electron
beam
to
be 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.
The Type
545A
Oscilloscope features two independent
time-base
units:
Time Base
A
and Time
Base
B.
Either of
the
two
time bases
may
be
displayed
on
the oscilloscope
screen
at
any
time.
Controls
affecting
Time
Base
A
and
Time Base
B
operation are
in
the
correspondingly labeled
blocks
on
the oscilloscope front panel.
The
HORIZONTAL
DISPLAY
switch determines which time base
is
used
and
the
type of display
to
be presented. Time Base
A
is
selected
when
the
HORIZONTAL
DISPLAY
switch
is
in
position
A
and Time Base
B
is
selected
when
the switch
is in
posi-
tion B.
Fig.
2-4.
The
oscilloscope
plots instantaneous voltage versus time,
thereby
serving
both
as a voltmeter
and
a
timer.
The
rate at which the spot
is
deflected across
the screen
is
accurately controlled by
the setting of the appropriate
TIME/CM
controls.
The
settings of the
TIME/CM
controls
determine
the
sweep
speed
and
the horizontal
size of the
displayed waveform. The
controls
are
set to
display
the
portion of the
waveform
you wish
to
observe.
Time
Base
A
has 24
accurately calibrated
sweep
rates
ranging from
.1
microsecond
to
5 seconds per
centimeter.
These
calibrated
sweep
rates
are obtained only when
the
VARIABLE TIME/CM
control
is
in
the
fully
clockwise
posi-
tion.
The
VARIABLE TIME/CM
control
permits you
to
vary
the
sweep
rate continuously
between
.1
microsecond
and
approximately
12 seconds per
centimeter.
All
sweep
rates
obtained
with the
VARIABLE TIME/CM
control
in
any
posi-
tion but fully
clockwise are
uncalibrated. Uncalibrated
sweep
rates
are
indicated
when
the
UNCALIBRATED
lamp
is
lit.
Time Base
B
has
sweep
rates
ranging from
2
microseconds
to
1
second per centimeter
in
18
steps.
There
is
no VARI-
ABLE TIME/CM
control for
Time Base
B.
The
red
LENGTH
control adjusts the
sweep
length
between
approximately
4
and
10 centimeters.
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 at a
rate
unrelated
to
the
rate of occurrence
of
the
input
waveform,
the displayed
waveform
will
be
traced out
at
a
different point
on
the
screen each time
the
sweep
runs. This will either
cause
the
waveform
to
drift
across the screen or
to
be
indistinguish-
able.
In
most
cases
it is
desirable
for a repetitive
waveform
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
appearance
of the input
waveform.
This
means
that
the
sweep
must be synchronized
with the input
waveform.
In
the
Type 545A
Oscilloscope
this
is
accomplished by
starting (triggering) the
sweep
with the
displayed wave-
form
or with
another
waveform
bearing
a definite time
relationship
to the
displayed waveform.
The
following paragraphs
outline the
means
for selecting
the triggering source, triggering slope,
and
triggering level
with
specific information
regarding
the operation
of the
controls
affecting triggering.
Triggering
controls
for
Time
Base
A
and
Time
Base B are
virtually identical so that the
following information
is
applicable
to
both time-base
units.
Triggering
of the
sweep
is
adjusted by
the respective
STABILITY,
TRIGGERING
LEVEL,
TRIGGERING MODE,
and
TRIGGER SLOPE
controls.
Selecting the Triggering
Source
In
preparing
the
Type 545A
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,
a line-frequency
waveform,