2.
The vertical and horizontal positioning controls permit you to shift the
position of the entire display to any portion of the viewing area desired.
The
vertical positioning control is a continuously variable potentiometer that permits
the display to be moved up and down by any amount, including those positions away
from the viewing area. Similarly, the horizontal positioning permits the side-to-
side movement of the entire display.
3.
Occasionally, while examining a waveform, you may notice irregularities at or
near some extremity of the display. You can enlarge the display using other scope
controls, and then position it by using the horizontal and vertical position
controls, so the irregularity appears within the viewing area.
The remainder of
the signal, of which the irregularity is only a small part, is then deflected off
the screen toward the neck of the cathode-ray tube, where it cannot be viewed. At
the edges of the tube, the display being deflected off the screen widens and
becomes considerably blurred at the rim of the tube. This distortion is caused by
the curvature and the reinforcing thickness of the glass.
4.
The coarse and fine sweep frequency controls of a scope provide for changing
the frequency of the sawtooth sweep generator output (fig 2-2).
The coarse
frequency control is generally a multiposition rotary switch used to select the
desired range of sawtooth frequency by changing the forward sweep time charging
capacitor. The fine frequency control is a potentiometer used to adjust the sweep
time constant (TC) to obtain the exact frequency needed for suitable display.
a. Selecting different shapes of the horizontal amplifier signals is also
determined by the setting of the coarse frequency control. Five or six positions
of the coarse frequency control are used to cover the full frequency range of the
internal sawtooth sweep generator.
b. Sinewave signals are widely used for time base sweep applications.
Such
signals are easily obtained from the 60-Hz power source within the scope.
The
sawtooth sweep generator is disabled by the coarse frequency control when either
the line sweep function or the direct function is selected.
5.
With the fine frequency control and the coarse frequency control, you can
select the time base required to display as many cycles or pulses as desired to
view the waveform.
Except for markings which aid in estimating some previous
position, the fine frequency control is not calibrated because the time base
frequency is only used as a means of obtaining a convenient display.
6.
injecting a known frequency into the vertical amplifier and manipulating the coarse
and fine frequency controls for a stationary pattern of one cycle. If the injected
signal is a 60-Hz sinewave, one sinewave lasting 1/60 of a second is displayed by
one sawtooth lasting for 1/60 of a second.
Therefore, the frequency of the time
base generator is also 60 Hz and is a 1-to-1 frequency ratio, as shown in Figure 2-
6.
43
Previous Page
