Figure 2-4.
Beam intensity affected by spot velocity
f. The basic controls that determine the size of the display are
potentiometers used as horizontal and vertical gain controls.
Adjustment of the
horizontal gain control increases or decreases the height of the display.
(1) An attenuator (occasionally referred to as a multiplier) is sometimes
used prior to adjusting the gain control.
It is associated with the vertical
amplifier and is calibrated in steps of 1x, 3x, 10x, 30x, and 100x.
The
attenuation at each step is expressed with respect to the attenuation range at step
1x.
Operation of this control results in abrupt changes in the scope display
because of step attenuation of the input signal level.
(2) The attenuator is called a multiplier because the attenuator output is
usually larger than the vertical amplifier input.
The scope can be used as a
direct-reading, peak-to-peak voltmeter once the vertical amplifier is calibrated.
Calibrate the amplifier by setting the attenuator to 1x, inject a signal of known
amplitude, and adjust the display to vertical dimensions of convenient known
height.
Advancing the gain control too far for a given signal, or applying a
signal that exceeds the amplification capabilities of the horizontal or vertical
amplifiers, results in overloading.
g. Interpretation of an observed waveform depends greatly upon proper
proportioning of the horizontal and vertical dimensions of the scope display.
Uncertainty or lack of knowledge concerning the signal that an amplifier is
processing, together with improper display proportioning, can lead to an erroneous
conclusion concerning the test circuit.
Figure 2-5b shows the display of a
trapezoidal waveform where the horizontal and vertical dimensions are acceptable.
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