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edge, which is coming from a negative potential and rising
to a positive potential. That 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. A falling edge
(minus sign) triggers, when the +/— button is depressed.
However, with normal triggering, the trigger point may be
varied within certain limits on the chosen edge using the
LEVEL control.
Trigger coupling
The coupling mode and accordingly the frequency range of
the trigger signal can be changed using the TRIG. selector
switch. However, this is possible only with the TV SEP.
switch in OFF position.
AC: Trigger range = 10Hz to 20MHz.
This is the most frequently used trigger mode.
The trigger threshold is increasing below 10 Hz.
DC: Trigger range DC to 20MHz.
DC triggering is recommended, if the signal ts to
be triggered with quite slow processes or if pulse
signals with constantly changing pulse duty fac-
tors have to be displayed.
Always
work
with
normal
triggering
and
LEVEL adjustment.
Otherwise there is the possibility in the AT posi-
tion (automatic triggering) that the trigger point
may change or that triggering may not occur with
signals
without
zero
crossing
(e.g. with
DC
offset). The balance of the corresponding channel
input should then be corrected (see "DC Balance
Adjustment", page M7). Sometimes triggering is
easier with AC input coupling, because the sig-
nal then has its average value exactly at the oscil-
loscope's ground potential.
HF: Trigger range 1.5kHzto40MHz
(high-pass filter).
The HF position is suitable for all radio-frequency
signals.
DC
fluctuations
and
low-frequency
excess noise of the trigger voltage are suppres-
sed, giving a stable display. The trigger threshold
increases below 1.5kHz.
LF: Trigger range DC to 1kHz_
(low-pass filter).
The LF position is often more suited for low-fre-
quency signals than the DC position, because the
(white) noise in the trigger voltage is strongly sup-
pressed. So jitter or double-triggering of complex
signals .is avoidable or at least reduced, in particu-
lar with very low input voltages.
The trigger
threshold increases above 1 kHz.
Line triggering
A part of a secondary winding voltage of the power trans-
former is used as mains/line frequency trigger signal (50 to
60 Hz) in the ~ position of the TRIG. selector switch. This
trigger mode is independent of amplitude and frequency of
the Y signal and is recommended
for all mains/line syn-
chronous signals. This also applies — within certain limits —
to whole number multiples or fractions of the line fre-
quency. Line triggering can also be useful to display signals
below the trigger threshold (less than
5mm). It is therefore
particularly suitable for measuring small ripple voltages of
mains/line rectifiers or stray magnetic field in a circuit.
Magnetic leakage (e.g. from a power transformer) can be
investigated for direction and amplitude using a search or
pick-up coil. The coil should be wound on a small former
with a maximum of turns of a thin lacquered wire and con-
nected to a BNC connector (for scope input) via a shielded
cable. Between cable and BNC center conductor a resistor
of at least 100@ should be series-connected (RF decou-
pling). Often it is advisable to shield statically the surface of
the coil.
However,
no shorted
turns
are permissible.
Maximum, minimum, and direction to the magnetic source
are detectable at the measuring point by turning and shift-
ing the coll.
Triggering of video signals
The built-in active TV-Syne-Separator (separation of the
sync pulses from the video signal and following amplifica-
tion) even allows the display of noisy, changing in amplitude
or distorted video signals, alternatively triggered with line
(or horizontal) frequency or frame (or vertical) frequency.
The TV SEP. lever switch has three positions. The OFF
position serves to all normal operations; the TRIG. selector
switch is operative. The TV: H position (horizontal 4 line)
and the TV: V position (vertical & frame) are used for video
triggering. The TRIG. coupling switch is inoperable in these
both positions. In the TV: V position (frame triggering), a
low-pass filter or integrating network is connected into cir-
cuit, which forms a trigger pulse sequence with frame fre-
quency from the vertical sync pulse (incl. pre- and post-
equalizing pulses).
For accurate function of the sync separator, the slope of the
sync pulses should correctly be adjusted (corresponding to
the position of the sync pulses in the composite color sig-
nal. If the sync pulses are placed above the picture content,
the +/— button should be released. The trigger point lies on
the rising front edge of the sync pulse. If they are below the
picture content, the +/— button should be depressed. The
trigger point lies on a falling (negative) front edge of the sync
pulse. This setting of the slope is valid for line and frame fre-
quency. An incorrectly set slope results in an unstable dis-
M12 203-6
Subject to change without notice
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