Tektronix 4S1 Instruction Manual page 20

Lagging waveform
Fig. 2-16. (a) Dual trace display of 100 Mc sinewave at sweep
rate of 2nsec/cm; (b.) Same display with sweep calibrated at 45
degrees /cm.
5, Measure the horizontal difference in centimeters be-
tween corresponding points on the two phases.
6. Multiply the difference in centimeters by the number
of degrees per centimeter. This product is the phase dif-
ference in degrees.
The "leading" waveform is generally considered to be
the one to the left on the crt display. This nomenclature is
only relative, however, since either waveform can be called
the leading one on the display. If one signal is known to be
from a signal source and the other is a response waveform,
the source waveform usually leads the response.
X-Y Method
To measure the phase difference between two sine waves
of the same frequency, using an X-Y display, proceed as
1. Set the front-panel controls of the Type 481 as indicated:
@L
Operating Instructions — Type 4$1
MODE B ONLY
DISPLAY (both channels) NORMAL
DC OFFSET (both channels) Midrange
TRIGGERING A or B as desired
SMOOTHING (both channels) NORMAL
2. With an unmagnified sweep, set the triggering con-
trols of the timing unit for a stable display showing from
one to five cycles of the input waveform.
3. Adjust the Channel B controls to obtain a display of
approximately 4 to 7cm of vertical deflection. Do not use
the VARIABLE control, since it will not be in the circuit in
4, Set the MODE switch to A ONLY and adjust the Chan-
nel A controls for approximately the same display amplitude
5. Set the MODE switch to A VERT. B HORIZ.
6. Center the display on the graticule with the Channel A
VERT. POSITION control and either the Channel B DC OFF-
SET or the oscilloscope Horizontal Position control. The dis-
play at this point will probably be an ellipse. If the dis-
play appears as a diagonal straight line the two sine waves
are either in phase (tilted upper right to lower left}, or 180°
out of phase (tilted upper left to lower right). If the display
is a circle, the two sine waves are 90° out of phase. In
any case, these instructions apply for measurement of phase
differences.
Fig. 2-17. X-Y method of calculating phase difference (9) between
7. Measure the distance 'A' and 'B' on the display as
shown in Fig. 2-17. 'A' divided by 'B' equals the sine of the
phase angle between the two sine waves.
ALGEBRAIC ADDITION
Signal Addition
The sum of two input signals may be obtained by placing
the MODE switch in the ADDED ALGEB. position and the