34
Subject to change without notice
Trigger coupling
Instrument specific information regarding this item can be
noted in the ”Data Sheet”. The coupling setting (
TRIG. MODE
(20)
) and indication are described under ”Controls and
Readout”.
As the automatic triggering does not work below 20Hz, normal
triggering should be used in DC and LF trigger coupling mode.
The coupling mode and accordingly the frequency range of
the trigger signal should meet the signal requirements.
AC:
This is the most frequently used trigger mode. The trigger
threshold increases below and above the frequency limits
mentioned in the data sheet. This filter cuts off both the
DC content of the trigger signal and the lowest frequency
range.
DC:
In this coupling mode the trigger signal is coupled
galvanically to the trigger unit if normal triggering (NM) is
present. Therefore there is no low frequency limit.
DC triggering is recommended if the signal is to be
triggered with quite slow processes or if pulse signals
with constantly changing pulse duty factors have to be
displayed.
HF:
In this coupling mode the transmission range equals a
high pass filter. It cuts off the DC content of the trigger
signal and the lower frequency range.
LF:
LF trigger coupling has a low pass filter function
characteristic. As in DC trigger coupling, there is no limit
for the pass frequency range in connection with normal
triggering.
The LF trigger coupling is often more suitable for low
frequency signals than DC trigger coupling because the
noise components of the trigger signals are strongly
suppressed. This avoids or reduces, under borderline
conditions, jitter or double traces especially with very low
signal voltages. The trigger threshold rises continuously
above the pass band.
Tv-L:
The built in active TV Sync Separator provides the
separation of line sync pulses from the video signal.
Even distorted video signals are triggered and displayed
in a stable manner. This mode is described under paragraph
”Triggering of video signals”.
Tv-F:
The built in active TV Sync Separator also provides the
separation of frame sync pulses from the video signal.
Even distorted video signals are triggered and displayed
in a stable manner.
This mode is described under paragraph ”Triggering of
video signals”.
~
:
Indicates “line/mains triggering” and is described under
the paragraph of the same name.
Triggering of video signals
In
Tv-L
and
Tv-F
trigger coupling mode the instrument is
automatically set to automatic triggering and the trigger point
indicator is switched off. As only the separated synchronization
pulses are used for triggering the relationship between the
displayed signal and the trigger signal is lost. In
TV-F
mode
interference may occur if chopped
DUAL
mode is chosen or
the readout is active.
The automatic triggering works above 20Hz. The failure of
automatic triggering at frequencies below 20Hz is abrupt.
However, it is not signified by the trigger indicator LED which
may still be blinking. Break down of triggering is best
recognizable at the left screen edge (the start of the trace in
differing display height).
The automatic peak (value) triggering operates over all
variations or fluctuations of the test signal above 20Hz.
However, if the pulse duty factor of a square wave signal
exceeds a ratio of 100:1, switching over to normal triggering
will be necessary. Automatic triggering is practicable with
internal and external trigger voltage.
Normal Triggering
Information specific to the instrument is given in the sections
NM - AT - (9)
,
LEVEL (11
)
)
)
)
) and
TRIG. MODE (20)
in the
paragraphs ”Controls and Readout”. The time fine adjustment
(((((VAR.), and the hold off time setting assist in triggering under
specially difficult signal conditions.
With normal triggering, the sweep can be started by AC
AC
AC
AC
AC
signals within the frequency range defined by the trigger
coupling setting.
In the absence of an adequate trigger signal or when the trigger
controls (particularly the trigger
LEVEL
control) are misadjusted,
no trace is visible.
When using the internal normal triggering mode, it is possible
to trigger at any amplitude point of a signal edge, even with
very complex signal shapes, by adjusting the trigger
LEVEL
control. If the signal applied at the Y input is used for triggering
(internal trigger source), its adjusting range is directly
dependent on the display height, which should be at least
0.5div. If it is smaller than 1div, the trigger
LEVEL
adjustment
needs to be operated with a sensitive touch. In the external
normal triggering mode, the same applies to approx. 0.3Vpp
external trigger voltage amplitude.
Other measures for triggering of very complex signals are the
use of the time base variable control and
HOLD OFF
time
control, mentioned below.
/ \
SLOPE
Please note item (9) in section ”Controls and Readout”
for instrument specific information.
The actual slope setting is displayed in the readout. The
setting is not changed by the
AUTOSET
AUTOSET
AUTOSET
AUTOSET
AUTOSET function. The slope
setting can be changed for the delay timebase trigger unit
in delay mode if the delay trigger function is active. The
previous slope setting for the undelayed time base trigger
is stored and still active. For further information please note
”Controls and Readout”.
The time base generator can be triggered by a rising or falling
edge of the test signal. Whether the rising or the falling edge
is used for triggering, depends on the slope direction setting.
This is valid with automatic and normal triggering. The positive
slope direction means an edge going from a negative potential
and rising to a positive potential. This has nothing to do with
zero or ground potential or absolute voltage values. The positive
slope may also lie in a negative part of a signal.
However the trigger point may be varied within certain limits
on the chosen edge using the LEVEL
LEVEL
LEVEL
LEVEL
LEVEL control. The slope
direction is always related to the input signal and the non
inverted display.
Triggering and time base
