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 DLY
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
us.
If an interval begins less
than 0.05 division from the beginning of A Sweep, the readout shows a
question mark. Move A 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
MS
or for low repetition rate signals that make the
display flicker, you may prefer to use the B Sweep without At. Without At, the display
repetition rate is higher and the Dly 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 At or 1/At.
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 DLY. (If an A-Trigger
Mode indicator is on, the B-Trigger has been set previously to RUN AFT DLY.)
4.
Set A REF OR DLY 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 (ALT mode). Use TRACE SEP to separate the
A-Sweep and B-Sweep traces.
6. Set A REF OR DLY POS to align the end of the interval with the left end of the
B Sweep. The DLY 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.
2-20 2465B/2455B/2445B Operators
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