Operation
Delta-Delay-Time Measurement Characteristics
A delta-delay-time measurement is valid between a pair
of
points
superimposed on the pair of B
Sweeps, regardless of display positions, Trace
Sep setting, and CRT-distortion errors.
In
other words, the only points that can
be
superimposed are those
pOints
that are separated by the delta-time value.
(Good accuracy for short intervals does depend on correct
CH
2 DL Y
adjustment. See "Operator Checks and Adjustments' section.)
The main sweep trigger event begins the interval
of
interest for many
measurements. The delta-delay-time measurement can include the
A-Sweep
trigger event with A SEC/DIV set faster than 50 IlS. If
an
interval begins less
than 0.05 division from the beginning of A Sweep, the readout shows a
question mark. Move
~
REF clockwise and change the A-Trigger controls
as
required
to
eliminate the question mark and still see a suitable waveform feature
for the beginning of the
interval.
Single-Delay-Time Measurements
For intervals longer than 10 IlS or for low repetition rate signals that make the
display
flicker, you may prefer
to
use the B Sweep without
~t.
Without
~t,
the display
repetition rate
is
higher and the Diy readout shows the time from the start of A Sweep
to the start of B Sweep. Compared to delta-delay-time measurements, some accuracy
will
be
lost, unless you can take the difference between one delay time and another.
1 . Display the time interval with the A
Sweep running as fast as possible,
unmagnified.
If the interval
is
a propagation delay or other two-signal
measurement, apply the signals
to
CH
1 and
CH
2.
For maximum display
repetition rate, display
only the channel with the end of the interval. Trigger
the A
Sweep at the beginning
of
the interval. Turn off
~t
or
1/~t.
2.
Pull
SEC/DIV out to activate B Sweep and light both the A SWP and B SWP
indicators (INTEN mode).
3.
If a B-Trigger Mode indicator is on, select
RUN
AFT DL
Y.
(If
an
A-Trigger
Mode indicator
is
on, the B-Trigger has been set previously
to
RUN
AFT DL Y.)
4.
Set
~
REF
OR
DL Y POS
to
place the intensified zone at the end of the
interval.
5.
Turn SEC/DIV clockwise with the knob pulled out to magnify the end
of
the
interval on the B
Sweep while observing its relationship
to
the beginning of the
interval
on
the A Sweep (AL T mode). Use TRACE SEP
to
separate the A-
Sweep and B-Sweep traces.
6.
Set
~
REF
OR
DL Y POS to align the end
of
the interval with the left end of the
B
Sweep. The DL Y reading
is
the length of the interval.
7.
If you want
to
simplify the display and obtain the best possible view
of
the end
of the interval, push the
SEC/DIV knob
in
when A and B SEC/DIV settings are
unequal
to
display only the B Sweep.
2-16 2465A/2455A/2445A Operators
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