16
Subject to change without notice
Triggering and time base
The most important controls and displays for these functions
are to be found in the shaded TRIGGER area, they are described
in „Controls and Readout“.-
In YT mode the signal will defl ect the trace vertically while the
time will defl ect it horizontally, the speed can be selected.
In general periodic voltage signals are displayed with a peri-
odically repeating time base. In order to have a stable display,
successive periods must trigger the time base at exactly the
same time position of the signal (amplitude and slope).
STOP
Pure DC can not trigger the time base, a voltage
change is necessary.
Triggering may be internal from any of the input signals or
externally from a time related signal.
For triggering a minimum signal amplitude is required which
can be determined with a sine wave signal. With internal trigge-
ring the trigger take off within the vertical amplifi ers is directly
following the attenuators. The minimum amplitude is specifi ed
in mm on the screen. Thus it is not necessary to give a minimum
voltage for each setting of the attenuator.
For external triggering the appropriate input connector is used,
thus the amplitude necessary there is given in V
pp
. The voltage
for triggering may be much higher than the minimum, however,
it should be limited to 20 times the minimum. Please note that
for good triggering the external voltage should be a good deal
above the minimum. The scope features two trigger modes to
be described in the following:
Automatic peak triggering (MODE menu)
Consult the chapters MODE
16
>
AUTO, LEVEL A/B
15
, FILTER
17
and SOURCE
18
in ”Controls and Readout“. Using AUTOSET
this trigger mode will be automatically selected. With DC coup-
ling and with alternate trigger this mode will be left while the
automatic triggering will remain.
Automatic triggering initiates a new time base start at the end
of each sweep, and after the hold off time has elapsed; even
without any input signal. Thus there is always a visible trace.
The position of the trace(s) without any signal is then given by
the settings of the POSITION controls.
As long as there is a signal, scope operation will not need more
than a correct amplitude and time base setting. With signals
<
20 Hz their period is longer than the time the auto trigger
circuit will wait for a new trigger, consequently the auto trigger
circuit will start the time base irrespective of the signal. Hence
the display will not be triggered and free run, quite independent
of the signal’s amplitude which may be much larger than the
minimum.
Also in auto peak trigger mode, the trigger level control is active.
Its range will be automatically adjusted to coincide with the
signal’s peak to peak amplitude, hence the name. The trigger
point will thus become almost independent of signal amplitude.
This means that even if the signal is decreased the trigger will
follow, the display will not loose trigger. As an example: the
duty cycle of a square wave may change between 1:1 and 100:1
without loosing the trigger.
Depending on the signal the LEVEL A/B control may have to be
set to one of its extreme positions.
The simplicity of this mode recommends it for most uncompli-
cated signals. It is also preferable for unknown signals.
This trigger mode is independent of the trigger source and
usable as well for internal as external triggering. But the signal
must be
>
20 Hz.
Normal trigger mode (See menu MODE)
Consult the chapters: MODE
16
>
AUTO, LEVEL A/B
15
, FILTER
17
and SOURCE
18
in ”Controls and Readout“. Tools for trigge-
ring very diffi cult signals can be found in the HOR VAR menu
26
where the functions time base fi ne adjustment VAR, HOLD OFF
time setting, and time base B operation are available.
With normal triggering and suitable trigger level setting, trigge-
ring may be chosen on any point of the signal slope. Here, the
range of the trigger level control depends on the trigger signal
amplitude. With signals
<
1 cm care is necessary.
In normal mode triggering there will be no trace visible in the
absence of a signal or when the signal is below the minimum
trigger amplitude requirement!
Normal triggering will function even with complicated signals. If
a mixture of signals is displayed triggering will require repetition
of amplitudes to which the level can be set. This may require
special care in adjustment.
Slope selection (Menu FILTER)
After entering FILTER
17
the trigger slope may be selected using
the function keys. See also ”Controls and Readout“. AUTOSET
will not change the slope.
Positive or negative slope may be selected in auto or normal
trigger modes. Also, a setting ”both“ may be selected which will
cause a trigger irrespective of the polarity of the next slope.
Rising slope means that a signal comes from a negative po-
tential and rises towards a positive one. This is independent
of the vertical position. A positive slope may exist also in the
negative portion of a signal. This is valid in automatic and
normal modes.
Trigger coupling (Menu: FILTER)
Consult chapters: MODE
16
>
AUTO, LEVEL A/B
15
, FILTER
17
and SOURCE
18
in ”Controls and Readout“. In AUTOSET DC-
coupling will be used unless AC coupling was selected before.
The frequency responses in the diverse trigger modes may be
found in the specifi cations.
With internal DC coupling with or without LF fi lter use normal
triggering and the level control. The trigger coupling selected
will determine the frequency response of the trigger channel.
AC:
This is the standard mode. Below and above the fall off of the
frequency response more trigger signal will be necessary.
DC:
With direct coupling there is no lower frequency limit, so this
is used with very slowly varying signals. Use normal triggering
and the level control. This coupling is also indicated if the signal
varies in its duty cycle.
T r i g g e r i n g a n d t i m e b a s e
