Subject to change without notice
28
Triggering and Timebase
Photo 1
(composite video signal)
MODE: undelayed
TIME/DIV: 5ms/div
Trigger coupling: TV-F
Trigger slope: falling ( - )
Pressing and holding the
SEA./DEL.
button switches over to
SEARCH
mode (
SEA
displayed by the readout).
In all delay modes, the
DEL. POS.
knob assumes the function
of DEL. POS. (delay position), and the hold off time defaults
to minimum. Now the function of this knob
(DEL. POS.)
is to
adjust the delay time, indicated as a blanked part of the
screen. The length of the blanked sector depends on the
DEL.
POS.
setting and can be set between approx. two and seven
division after the normal trace start position. As the trace right
end is not effected, the visible trace length is reduced. In delay
(DEL)
mode, the trace will start from the normal left end
where the blanking starts. If the maximum delay is not
sufficient, the time coefficient must be increased (
TIME/DIV
knob) and the
DEL. POS.
knob set to the later starting point.
To return to normal (undelayed) time base operation, press
and hold the
SEA./DEL
pushbutton again.
Photo 2
MODE: SEA (SEARCH)
TIME/DIV: 5ms/div
Trigger coupling: TV-F
Delay time:
4div x 5ms = 20ms
Figure 2 shows that the delay time can be measured. It is
identical with the displacement of the start of the trace. One
can calculate this by multiplying the blanked out section
(horizontal) by the time deflection coefficient setting.
The total trace starting with the previously selected section
will be visible when switched from
SEARCH
to
DELAY
,
providing the (stored) current time deflection coefficient is not
too small.
If the trace is invisible or hardly visible because of too high
expansion (too small deflection coefficient), the time deflection
coefficient must be increased with
TIME / DIV
knob. A larger
deflection coefficient than in the
SEARCH
mode cannot be
set.
Example:
The SEARCH setting selected in figure 2 is 5ms/cm. The
display in DELAY mode, also with 5ms/cm is delayed but
unexpanded (1:1). A further increase in the deflection
coefficient, e.g. 10ms/cm would be meaningless and
therefore automatically blocked.
Please note that the previous time coefficient chosen in
DEL
and
DTR
mode is stored and automatically set after activating
one of those modes. If the stored time coefficient in
DEL
or
DTR
mode was higher than the actual value in
SEA
(search)
mode, the time coefficient in
DEL
or
DTR
mode is automatically
set to the value used during SEA (search) operation.
Photo 3
MODE: DEL (DELAY)
TIME/DIV: 5ms/div
Trigger coupling: TV-F
Trigger slope: falling ( - )
Delay time: 20ms
Reducing the time coefficient (increasing the time base
speed) now expands the signal. If the signal start position is
not set to the optimum, it can still be shifted in the X direction
by turning the
DEL. POS.
knob. Photo 4 shows a 50 fold X
magnification caused by setting the time coefficient to 0.1ms/
div (5ms/div : 0.1ms/div = 50). The reading accuracy also
increases with higher X magnification. As already mentioned,
the time variable control must be in
CAL
position when
measurements are taken.
Photo 4
MODE: DEL (DELAY)
TIME/DIV: 0.1ms/div
Trigger coupling: TV-F
Trigger slope: falling ( - )
Delay time: 20ms
The delayed and expanded signal display can be triggered
again if a signal slope suitable for triggering appears after the
delay time. For this, one must switch to
DEL.TRIG.
(2nd
triggering after the expiry of the delay time - after Delay
Triggering). The settings selected before switching, automatic
Peak value triggering / Normal triggering, trigger coupling,
the trigger
LEVEL
setting and slope setting, remain valid and
trigger the start of the delay time.
The
”After Delay”
Triggering automatically switches to
normal triggering (indicated by the
NM LED
) and DC trigger
coupling. These default conditions cannot be changed. But
the trigger level (
LEVEL
) and the trigger slope direction can
be altered in order to enable the triggering at the desired
signal section. The trace does not start and the screen
remains blank if the signal amplitude is not sufficient for
triggering or if the setting of the trigger
LEVEL
is unsuitable.
The expanded display can also be displaced in the X direction
with
DELAY
position control (
DEL.POS.
) under suitable
settings. However, the displacement is not continuous as in
the untriggered
DELAY
operation but jumps from one trigger
slope to another - with most signals this is not evident. This
means, in the case of TV Triggering, that it is possible to
trigger not only with line synchronizing pulses but also on
suitable slopes occurring within the line.
Of course, the magnification is not restricted to a factor 50
as mentioned in the example. The limit is given by the
increasing loss of trace intensity as the magnification is
increased.
The manipulation of time delay requires a certain experience
, especially with complicated signal combinations which are
difficult to display. The recording of signal sections of simple
signals is, in contrast, from the beginning fairly easy. The
time delayed display is also possible in the dual channel,
addition and difference modes.
