mode (VERT MODE set to DUAL), and with alter-
nate sweep only (PULL CHOP not engaged).
3.
In the EXT position, the signal applied to the EXT
TRIG jack becomes the trigger source. This signal
must have a timing relationship to the displayed wave-
forms for a synchronized display.
4.
In the LINE position of the COUPLING switch,
triggering is derived from the input line voltage (50/60
Hz) and the trigger SOURCE switch is disabled. This
is useful for measurements that are related to line
frequency.
TRIG LEVEL/PULL (–) SLOPE Control
(Refer to Fig. 3)
A sweep trigger is developed when the trigger source
signal crosses a preset threshold level. Rotation of the TRIG
LEVEL control varies the threshold level. In the + direction
(clockwise), the triggering threshold shifts to a more posi-
tive value, and in the
−
direction (counterclockwise), the
triggering threshold shifts to a more negative value. When
the control is centered, the threshold level is set at the
approximate average of the signal used as the triggering
source. Proper adjustment of this control usually synchro-
nizes the display.
The TRIG LEVEL control adjusts the start of the sweep
to almost any desired point on a waveform. On sine wave
signals, the phase at which sweep begins is variable. Note
that if the TRIG LEVEL control is rotated toward its
extreme + or
−
setting, no sweep will be developed in the
normal trigger mode because the triggering threshold ex-
ceeds the peak amplitude of the sync signal.
When the PULL (–) SLOPE control is set to the + (“in”)
position, the sweep is developed from the trigger source
waveform as it crosses a threshold level in a positive-going
direction. When the PULL (–) SLOPE control is set to the
−
(“out”) position, a sweep trigger is developed from the
trigger source waveform as it crosses the threshold level in
a negative-going direction.
TIME BASE Control
Set the Time Base TIME/DIV control to display the
desired number of cycles of the waveform. If there are too
many cycles displayed for good resolution, switch to a faster
sweep time. If only a line is displayed, try a slower sweep
time. When the sweep time is faster than the waveform being
observed, only part of it will be displayed, which may appear
as a straight line for a square wave or pulse waveform.
HOLDOFF Control
(Refer to Fig. 4)
A “holdoff” period occurs immediately after the comple-
tion of each sweep, and is a period during which triggering
of the next sweep is inhibited. The normal holdoff period
varies with sweep rate, but is adequate to assure complete
retrace and stabilization before the next sweep trigger is
permitted. The HOLDOFF control allows this period to be
extended by a variable amount if desired.
This control is usually set to the MIN position (fully
counterclockwise) because no additional holdoff period is
necessary. The HOLDOFF control is useful when a com-
plex series of pulses appear periodically such as in Fig. 4B.
Improper sync may produce a double image as in Fig. 4A.
Such a display could be synchronized with the VAR
SWEEP control, but this is impractical because time meas-
urements are then uncalibrated. An alternate method of
synchronizing the display is with the HOLDOFF control.
The sweep speed remains the same, but the triggering of the
next sweep is “held off” for the duration selected by the
HOLDOFF control. Turn the HOLDOFF control clock-
wise from the MIN position until the sweep starts at the
same point of the waveform each time.
Slope “–” Range
Slope “+” Range
Level
+
–
Fig. 3.
Function of Slope and Level Controls.
OPERATING INSTRUCTIONS
A. Holdoff not used
B. Holdoff used
Fig. 4.
Use of HOLDOFF Control.
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