Appendix A – The Digital Oscilloscope
An oscilloscope is an instrument used to view signal amplitude,
frequency, and shape at different points throughout a circuit. We will
employ a dual trace digital oscilloscope, which uses fast analog-to-
digital converters to convert two channels of input (CH1, CH2) into
arrays (V1,t) and (V2,t) where V1 and V2 are voltages and t is time
represented by 2500 points, equally spaced by a set time interval t.
Since the data is digital, the oscilloscope can use a powerful
microprocessor to process and display the data in many ways,
although it is still most commonly used to display V1 and V2 versus
time. Oscilloscopes come with a wide variety of features and
functions, but the basic operational features are almost identical.
1. The Time Base: The oscilloscope contains circuits that produce a
beam of light that is swept continually from the left to the right of
the cathode-ray tube (CRT) screen. When no input signal is
applied, this sweep will produce a straight horizontal line in the
center of the screen. When an input signal is present, the
horizontal sweep is influenced by the input signal, which moves it
up and down to produce a pattern on the CRT screen the same as
the input pattern (sine, square, sawtooth, etc.). The sweep time/cm
switch selects the speed of the sweep from left to right, and it can
be either fast (0.2 s/cm) or slow (0.5 s/cm). A low-frequency input
signal (long cycle time or period) will require a long time setting
(0.5 s/cm) so that the sweep can capture and display one or more
cycles of the input.
2. Voltage measurement: The screen is divided into eight vertical and
ten horizontal divisions. This 8x10 cm grid is called graticule.
Every vertical division has a value depending on the setting of the
volts/cm control.
Channel 1 and 2 Vertical Controls: Volts/div knobs set the number of volts to be
displayed by each major division on the vertical scale of the screen. Position control
moves the trace up or down for easy measurement or viewing.
Appendix
A
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