2-17
WAVEFORM ANALYSIS
WAVEFORM ANALYSIS can be made by observing displays of voltage and current variations with
respect to time or by harmonic analysis of complex signals. Waveform displays are particularly valuable
for adjusting and testing pulse-generating, pulse-forming, and pulse-amplifying circuits. The waveform
visual display is also useful for determining signal distortion, phase shift, modulation factor, frequency,
and peak-to-peak voltage.
Waveform analysis is used in various electrical and electronic equipment troubleshooting. This
section will briefly discuss the oscilloscope and spectrum analyzer to provide you with basic knowledge
of this test equipment.
Q-9. Name two instruments used to analyze waveforms.
USE OF THE OSCILLOSCOPE
The CATHODE-RAY OSCILLOSCOPE (CRO or O-SCOPE) is commonly used for the analysis of
waveforms generated by electronic equipment. Several types of cathode-ray oscilloscopes are available
for making waveform analysis. The oscilloscope required for a particular test is determined by
characteristics such as input-frequency response, input impedance, sensitivity, sweep rate, and the
methods of sweep control. The SYNCHROSCOPE is an adaptation of the cathode-ray oscilloscope. It
features a wide-band amplifier, triggered sweep, and retrace blanking circuits. These circuits are desirable
for the analysis of pulse waveforms.
Oscilloscopes are also part of some harmonic analysis test equipments that display harmonic energy
levels. To effectively analyze waveform displays, you must know the correct wave shape. The
maintenance instructions manual for each piece of equipment illustrates what waveforms you should
observe at the various test points throughout the equipment. Waveforms that will be observed at any one
selected test point will differ; each waveform will depend on whether the operation of the equipment is
normal or abnormal.
The display observed on a cathode-ray oscilloscope is ordinarily one similar to those shown in figure
2-13. Views A and B show the instantaneous voltage of the wave plotted against time. Elapsed time (view
A) is indicated by horizontal distance, from left to right, across the etched grid (graticule) placed over the
face of the tube. The amplitude (view B) of the wave is measured vertically on the graph.
