Showing Waveforms with the Oscilloscope

Author: N.H. Crowhurst

Waveforms can actually be examined by means of the instrument known as an oscilloscope. It a special tube in which a beam or "pencil" of electrons is focused to a point on a fluorescent screen that glows with the impact of the electrons. Two pairs of deflecting plates bend the beam in accordance with the voltages applied to them.

Applying different voltages to the plates at the sides of the beam will move the spot sideways, and voltages applied to the upper and lower plates deflect the beam up or down. If different fluctuating voltages are applied to both pairs of plates, the spot will trace a pattern on the screen representing the combined effect of the two voltage fluctuations.

Cathode ray oscilloscope

If the fluctuation applied to the side plates follows a "sawtooth" waveform, the spot will move steadily from left to right across the screen, and then rapidly return to its starting point. By using this waveform as a "time-base" in this way, the voltage applied to the vertical plates traces its own waveform. In this way we can see the curvature distortion or clipping just discussed.

Sawtooth wave applied to horizontal plates makes spot travel steadily from left to right, then fly back to start again