BK Precision 4011A Instrucciones de operaciones descargar pdf (Pagina 65)

Appendix D: Operating Instructions for a Typical Oscilloscope

201053

Phase Angle Measurement

The difference in phase angle between two waveforms may be measured directly on the oscillo-

scope with little difficulty.

For an oscilloscope with only one vertical input:

One wave is chosen as the reverence and applied to the vertical input terminals. This same wave

is applied to the external trigger input of the scope. Next, a convenient point on the wave is se-

lected as a time reference, such as where the wave is zero and about to swing positive. Then, this

waveform is removed from the vertical input and a second waveform is applied. The voltage of

this wave at the time reference is observed. The ratio of voltage at the time reference to the

maximum voltage is equal to the sine of the phase difference between the two waves. This rela-

tion is shown below.

For an oscilloscope with two vertical inputs:

Connect the reference voltage to Channel 1 of the oscilloscope and connect the second voltage to

Channel 2. Adjust the amplitudes so the overlapping signals look something like the figure be-

low, where the solid curve is Channel 1 (the reference) and the dashed curve is Channel 2. (In

this figure, the dashed curve is lagging the solid curve; if the dashed curve were shifted to the left

so it “started” before the solid curve, then the dashed curve would be leading the solid curve.)

The phase shift



in degrees can be calculated by the following formula:



= t · f ·360°

where



is the phase shift, f is the frequency, and t is the time difference between the two wave-

forms. Many new digital scopes have cursors that allow directly marking, calculating, and dis-

playing the time difference and perhaps even the phase shift.

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BK Precision 4011A Instrucciones de operaciones Pagina 65