Leader LBO-516 Instruction Manual - page 17
cult. Triggering from the stable leading edge (+ slope) yields a
trace that has only the trailing-edge jitter of the original signal. If
you are ever in doubt, or have an unsatisfactory display, try both
slopes to find the best way.
The LEVEL control determines the point on the selected
slope at which the main (A) timebase or delayed (B) timebase will
be triggered. The effect of the LEVEL control on the displayed
trace is shown in Figure 2-9a. The +, 0, and - panel markings for
this control refer to the waveform's zero crossing and points more
positive (+) and more negative (-) than this. If the trigger slope is
very steep, as with square waves or digital pulses, there will be no
apparent change in the displayed trace until the LEVEL control is
rotated past the most positive or most negative trigger point,
whereupon the display will free run (AUTO sweep mode) or
disappear completely (NORM sweep mode). Try to trigger at the
mid point of slow-rise waveforms (such as sine and triangular
waveforms), since these are usually the cleanest spots on such
waveforms. As figure 2-9b shows, triggering on a noisy area will
cause instability in the display. Pulling the HOLDOFF control
outwards to the PRESET level position automatically triggers the
timebase near the zero-crossing point of the trigger signal.
The larger the amplitude of the trigger signal inputted to the
trigger circuits, the greater is the degree of rotation (control range)
over which the LEVEL control will maintain a stable display.
With internally-derived trigger, the actual trigger amplitude is
proportional to the number of graticule divisions occupied by the
trace. Therefore, the trigger point is more critical with small
signals than large. This is one reason why it is important to use as
much trace height as practical for the number of traces displayed.
The HOLDOFF control is used for special circumstances
only. It allows the operator to alter the mandatory "dead" time
between the end of one sweep and the start of the next (in
response to a trigger pulse). This prevents the triggering of
subsequent sweeps by the wrong trigger pulse in a complex
waveform. During normal operation, leave the HOLDOFF control
click-stopped at NORM. When viewing complex waveforms
containing multiple trigger points per repetition, rotate the
HOLDOFF control clockwise until the proper waveform is
secured, as shown in Figure 2-10. For example, the waveform
shown contains three pulses in each group capable of triggering
the timebase, but sweep must begin only on the first pulse in each
burst to obtain the proper display. In the lower display, the dead
time has been extended enough to make it impossible for last
pulse in the second burst to start the next sweep.
Rotate the HOLDOFF control fully clockwise to its B ENDS
A click-stopped position when using the delayed (B) timebase and
the difference between the A and B TIME/DIV setting is large (6
positions or more). The resulting brightness improvement is
greatest when the delay time between B and A timebases is short.
2-3-4 Probe Compensation
The LP- 100X probes furnished with the LBO-516 must be
adjusted to the input capacitance of the. channel(s) with which
they are used. If the probes are used only with vertical input
channels 1 and 2, this adjustment need be performed only when
the probes are first used, and the probes can be used
interchangeably between these channels without adjustment.
However, if an additional probe is purchased for the trigger input
channel (CH-3), mark it and compensate it separately, as the CH-3
input capacitance is somewhat different.
To compensate a probe for CH-1 or CH-2, proceed as fol-
lows:
1. Connect the probe to the CH-1 input connector (14) and the
CAL connector (9).
2. Set the CH- 1 VOLTS/DIV switch (10) to 20 mV, the CH- 1
AC/GND/DC switch (16) to DC, and the A TIME/DIV
switch (24) to .2 mS.
3. Press the CH-1 V MODE pushbutton (21) and A HORIZ
DISPLAY pushbutton (35), and select CH-1 SOURCE (34).
4. With a small screwdriver, adjust the capacitance-correction
trimmer (Figure 2-6a) for a correct-appearing square wave.
(Figure 2-6d).
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