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Trigger Point Selection. The SLOPE switch determines whether the sweep will
on a positive-going or negative-going transition of the trigger singal. (See
Figure 2-5). Always select the steepest and most stable slope or
edge. For example, small changes in the amplitude of the sawtooth shown in Figure
2-5A will cause jittering if the timebase is triggered on the positive (ramp) slope,
but have no effect if triggering occurs on the negative slope (a fast-fall edge).
In the example shown in Figure 2-5B, both leading and trailing edges are very steep
(fast rise and fall times). However, triggering from the jittering trailinge edge will cause
the entire trace to jitter, making observation difficult. 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 will be triggered. The effect of the LEVEL control on the displayed
trace is shown in Figure 2-5C. The
+,
0, and - panel markings for this control
refer to the wavefrom's zero crossing and points more posivive( +) 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 sopts on such waveforms.
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