b. Consider a sinewave input signal of 1500 Hz. The resultant scope display
is adjusted until a stationary pattern of three complete cycles is observed for one
sweep of the time base generator. The sweep is now displaying three cycles, with
each cycle lasting 1/1500 second, and there are 500 sweeps per second.
c. When the display includes one or more complete cycles of an input
waveform, whether completely stationary or not, the frequency of the time base
generator is equal to or lower than that of the input waveform.
In these cases
where the display is adjusted for a stationary pattern, the frequency of the time
base generator may be calculated by dividing the input frequency by the number of
complete cycles displayed.
9.
The synchronizing control provides for injecting a portion of the signal
being amplified in the vertical section into the time base generator to produce a
stationary waveform display.
Throughout this discussion about time base sweep
controls, we have emphasized the stationary display.
To obtain a stationary
display, the vertical amplifier input and the horizontal amplifier output have a
whole-number frequency ratio and an in-phase relationship.
10.
The synchronizing control potentiometer is used to inject as much of the
synchronizing signal as needed to produce a stationary display pattern.
The
adjustment of this control is not critical, but an excessive synchronizing signal
can severely distort the observed signal due to erratic functioning of the time
base generator.
a. When there is no synchronizing waveform injected into the time base
generator, the generator initiates a sweep when the potential on the plate is equal
to the ionizing potential of the generator tube.
The resulting sweep is free
running under these conditions because the sweep rate is governed by the frequency-
determining network of the generator. The display obtained may appear as a variety
of constantly changing patterns, depending upon the frequency of the generator with
respect to the waveform present in the vertical amplifier.
b. If the synchronizing control is advanced too far, the amplitude of the
synchronizing signal produces a distorted sweep signal.
The display obtained is
undesirable because it is difficult to visualize the type of signal applied at the
vertical input terminal.
However, the pattern remains stationary, being
continuously displayed as a single trace until corrective action is taken.
c. The synchronizing signal is often injected directly into the time base
generator from a source external to the scope. Its use is dependent chiefly upon
the type of signal undergoing observation and is especially useful for initiating
triggered sweeps.
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