Tektronix 545A Instruction Manual page 27

Applications
—
Type
545A
Sweep
Magnification
Time/cm
Switch
Setting Horizontal Distance
—
Time
Fig.
3-3.
Measuring
time
interval
between
events displayed on
the oscilloscope screen.
indicated
to
be
positive.
The
indicated
voltage
multiplied
by the probe's attenuation factor of 10 then gives
you
the
actual voltage of positive 6
volts.
Time
Measurements
The
calibrated
sweeps
of the
Type 545A
Oscilloscope
cause
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
sufficient
accuracy
for
most
applications
is
as
fol-
lows
(see
Figure
3-3):
1.
Using
the graticule,
measure
the horizontal distance be-
tween
the
two displayed events
whose
time
interval
you
wish
to find.
2.
Multiply the distance
measured by
the
setting of
the
appropriate
TIME/CM
control to
obtain
the
apparent time
interval.
(The
VARIABLE TIME/CM
control
must be
in
the
CALIBRATED
position).
3.
Divide the
apparent
time
interval
by
5
if
the
magnifier
is
on,
and
1 if
the
magnifier
is off,
to
obtain the actual
time
interval.
For
example, assume
that the
TIME/CM
switch
setting
is
1
MILLISEC,
the
MAGNIFIER
is
ON,
and
that
you measure
a
horizontal distance of 5 centimeters
between
events.
In
this
example
then,
5 centimeters multiplied by
1
millisecond
per centimeter gives
you an apparent
time
interval
of 5
milliseconds.
The apparent
time divided by
5 then gives
you
the actual time
interval of
1
millisecond.
Another method
for
measuring
time
intervals involves
the use of the
delayed
sweep
feature of the
Type 545A
Oscilloscope.
In this
method
the
HORIZONTAL
DISPLAY
switch
is
placed
in
the
'B'
INTENSIFIED BY
'A'
position
to
brighten a portion of the
trace.
The brightened
portion of
the trace
and
the
DELAY-TIME
MULTIPLIER
control
are
then
used
to
make
the time measurements.
This
method
provides
a very high degree
of
accuracy
when
care
is
taken
in
mak-
ing the measurements.
The method
is
summarized
as
follows:
1.
Place
the
HORIZONTAL
DISPLAY
switch
in
the
'B'
INTENSIFIED BY
'A' position
and
adjust the
Time Base
B
triggering controls
for
a
stable display of the input
wave-
form. Adjust
Time
Base
A
for free-running operation.
2.
Turn the
intensity
down
until the
brightened
portion of
the trace
is
easily distinguishable. Adjust the
Time Base
A
TIME/CM
controls to
reduce
the
brightened area
to a small
spot or to
cover as
small a portion of the trace
as possible.
3.
Using
the
DELAY-TIME MULTIPLIER
control, position the
start
of the
brightened
portion of the beginning of the
inter-
val
you wish
to
measure. Record
the
setting
of the
DELAY-
TIME MULTIPLIER
control.
4.
Using the
DELAY-TIME MULTIPLIER
control, position the
start
of the
brightened
portion of the trace to the
end
of
the interval
you
wish
to
measure.
Again
record the
setting
of the
DELAY-TIME MULTIPLIER
control.
3-3