Time Measurements - Philips PM2521 Service Manual

13
1.3.3. 2.
Time measurements
Time
measurements
of
signals are
determined
in
conjunction with the
trigger level
function
in
a similar
way
to
frequency measurements.
The
input
signal
is
applied
via
the
voltage attenuator to
one
input of the
comparator A502. The
selected
trigger level
is
applied to the other
input.
When
the
amplitude of
the
signal
exceeds
that of the selected trigger
level,
an
output
pulse
from
the
com-
parator
is
applied direct to the microprocessor.
Two
trigger
modes
are possible for the time measurement
function:
In
the normal
trigger
mode,
signals that
are
higher or lower than the
circuit
zero
(0
terminal of
PM2521
)
can
be triggered with the
-i-
or
—
trigger
level
respectively.
•(-TRIGGER
LEVEL
0
TRIGGER POINTS (+-(1
TRIGGER POINTS!
)
ST 301
6
S20226
Fig. 10.
Normal
trigger
mode
In
the special trigger
mode,
using
Data Hold Probe PM9263,
the
PM2521
triggers in
the
-i-
level
mode
on
positive
and
negative crossings of
the
trigger
level.
Conversely,
in
the
—
level
mode
it
triggers
on
negative
and
positive crossings
of the trigger
level.
•(TRIGGER
1
LEVEL
O'
TRIGGER POINTS!-!--)
TRIGGER points!—
(-1
A
1
\
°-i
:
i
1
'
p:
A 1
V
TRIGGER
LEVEL
ST 3016
820226
Fig.
1
1.
Special
trigger
mode
1.
3.3.3.
Trigger
measurements
In
addition to
time and frequency
applications,
the
trigger
level
function permits other selective
measurements
to be
made.
To
measure
the peak voltage of an input
signal
the front-panel trigger
level
control
is
rotated
until
the
GATE
indicator display
is
triggered either
on
or
off.
At
this
switch-over point the voltage indicated
on
the display
represents the amplitude or
peak
voltage of the input
signal.