Subject to change without notice
26
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 later.
- Slope
Please note item (12) 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
function. The slope setting
can be changed in alternate- and B time base mode for the B
time base trigger unit if the delay trigger function is active.
The previous slope setting for the A 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 and 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 control. The slope direction is
always related to the input signal and the non inverted display.
Trigger coupling
Instrument specific information regarding this item can be noted
in the “Data Sheet”. The coupling setting
( TRIG. MODE (23))
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.
threshold can be stated as vertical display height in div, at which
the time base generator starts, the display is stable, and the
trigger indicator LED lights or flashes. The internal trigger
threshold of the oscilloscope is given as
≤
0.5div. When the trigger
voltage is externally supplied, it can be measured in Vpp at that
input. Normally, the trigger threshold may be exceeded up to a
maximum factor of 20.
The instrument has two trigger modes, which are characterized
as Automatic- Peak and Normal-Triggering.
Automatic Peak (Value) -Triggering
Instrument specific information can be drawn from the items
NM - AT -
(12)
and
LEVEL (13)
in the section
“Controls and
Readout”
.
This trigger mode is automatically selected after the
AUTOSET
pushbutton is pressed. As the peak value detection makes no
sense in combination with
DC
and
TV
(television) signals, it is
switched off automatically in
DC
,
TVL
and
TVF
trigger coupling
conditions as well as in alternate trigger mode. In this case the
automatic is still present, but a wrong trigger level setting causes
an untriggered display.
In automatic trigger mode the sweep generator can run without
a test signal or external trigger voltage. A base line will always
be displayed even with no signal. With an applied AC signal the
peak value triggering enables the user to select the voltage point
on the trigger signal (trigger point), by the adjustment of the
trigger level control. The control range depends on the peak to
peak value of the signal. This trigger mode is therefore called
Automatic Peak (Value)- Triggering. Operation of the scope needs
only correct amplitude and time base settings, for a constantly
visible trace.
Automatic mode is recommended for all uncomplicated
measuring tasks. However, automatic triggering is also the
appropriate operation mode for the “entry” into difficult measuring
problems, e.g. when the test signal is unknown relating to
amplitude, frequency or shape. Presetting of all parameters is
now possible with automatic triggering; the change to normal
triggering can follow thereafter.
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 is
still blinking. Loss 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
The description of the most important control elements (
NM -
AT -
(12)
and
LEVEL (13)
) is part of the section
“Controls
and Readout”
).
With normal triggering, the sweep can be started by 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.
Triggering and Time Base
