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Appendix D: Operating Instructions for a Typical Oscilloscope

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Appendix D

Operating Instructions for a Typical Oscilloscope

The oscilloscope is an instrument for the analysis of electrical circuits by observation of voltage

and current waves. It may be used to study frequency, phase angle, and time, and to compare the

relation between two variables directly on the display screen. Perhaps the greatest advantage of

the oscilloscope is its ability to display the periodic waveforms being studied.

Until recently, oscilloscopes used a cathode-ray tube to display the signals of interest. A cathode-

ray tube (CRT) contains an electron gun that directs a high-velocity beam of electrons onto a

fluorescent screen. The beam is controlled by a pair of horizontal and a pair of vertical deflecting

plates. When the voltage on the deflection plates is equal to zero, the beam produces a spot of

light in the center of the screen. Any potential applied to the plates creates an electric field that

deflects the electron beam proportionally to the applied voltage.

A simple block diagram of the cathode-ray oscilloscope is shown below.

The basic components of the traditional oscilloscope are cathode-ray tube, amplifiers, sweep or

timing oscillator, and power supply. A voltage to be observed is applied to the vertical deflection

plates. This signal may be amplified by the vertical amplifier in order to obtain a satisfactory ver-

tical deflection. Meanwhile, a sweep oscillator moves the beam horizontally at a uniform rate.

The simultaneous horizontal and vertical sweep of the beam across the CRT screen displays the

waveform of the voltage applied to the vertical plates. The sweep oscillator blanks the CRT elec-

tron gun during its reverse sweep across the screen to switch off the electron beam.

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BK Precision 4011A Instrucciones de operaciones Pagina 62