 - An oscilloscope is a laboratory instrument commonly used to display
and analyze the waveform of electronic
signals. In effect, the device draws a graph of the instantaneous signal voltage as a function of time.
A typical oscilloscope can display alternating current (AC) or
pulsating direct current (DC) waveforms having a frequency as low as
approximately 1 hertz (Hz) or as high as several megahertz (MHz). High-end oscilloscopes can
display signals having frequencies up to several hundred gigahertz (GHz). The display is broken up into
so-called horizontal divisions (hor div) and vertical divisions (vert div). Time is
displayed from left to right on the horizontal scale. Instantaneous voltage appears
on the vertical scale, with positive values going upward and negative values going
downward.
The oldest form of oscilloscope, still used in some labs today, is known as the cathode-ray
oscilloscope. It produces an image by causing a focused electron beam to travel, or sweep, in patterns
across the face of a cathode ray tube (CRT).
More modern oscilloscopes electronically replicate the action of the CRT using a liquid crystal display (liquid crystal display) similar to those found
on notebook computers. The most sophisticated oscilloscopes employ computers to
process and display waveforms. These computers can use any type of display,
including CRT, LCD, and gas plasma.
In any oscilloscope, the horizontal sweep is measured in seconds per division
(s/div), milliseconds per division (ms/div), microseconds per division (s/div), or
nanoseconds per division (ns/div). The vertical deflection is measured in
volts per division (V/div), millivolts per division (mV/div), or microvolts per division
(?V/div). Virtually all oscilloscopes have adjustable horizontal sweep and
vertical deflection settings.
The illustration shows two common waveforms as they might appear when displayed on an
oscilloscope screen. The signal on the top is a sine wave; the signal on the bottom
is a ramp wave. It is apparent from this display that both signals have the
same, or nearly the same, frequency.
They also have approximately the same peak-to-peak
amplitude. Suppose the horizontal sweep rate in this instance is 1 µs/div.
Then these waves both complete a full cycle every 2 µs, so their frequencies are both
approximately 0.5 MHz or 500 kilohertz (kHz). If the vertical deflection is set for,
say, 0.5 mV/div, then these waves both have peak-to-peak amplitudes of approximately 2 mV.
These days, typical high-end oscilloscopes are digital devices. They connect to
personal computers and use their displays. Although these machines no longer employ
scanning electron beams to generate images of waveforms in the manner of the old
cathode-ray "scope," the basic principle is the same. Software controls
the sweep rate, vertical deflection, and a host of other features which can include:
- Storage of waveforms for future reference and comparison
- Display of several waveforms simultaneously
- Spectral analysis
- Portability
- Battery power option
- Usability with all popular operating platforms
- Zoom-in and zoom-out
- Multi-color displays
| LAST UPDATED: |
31 Jul 2001
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