Tektronix 503, Инструкция по эксплуатации

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O perating Instructions— Type 503
3. M ultiply the disance measured by the setting of the
SWEEP TIME/CM control and divide by the setting o f the
HORIZONTAL DISPLAY switch ( X I , X 2 , X 5 , etc.). This
is the time interval between the two points measured.
NOTE
Errors caused by a lack o f resolution can be re ­
duced b y e x p a n d in g the displayed w aveform fo r
a 1-cycle presentation between the first and ninth
g ra tic u le lines.
To determine the frequency of a recurrent waveform,
simply take the reciprocal of the time interval between
corresponding points on two consecutive cycles of the wave­
form.
Phase-Shift Measurements
To measure the phase shift produced in a given signal
by some device, proceed as follows:
1. Set up the oscilloscope for conventional externally trig ­
gered operation with the signal at the input to the phase-
shifting device applied to either of the vertical INPUT con­
nectors.
2. Horizontally position the display so that an easily
identifiable point of a cycle corresponds to one of the ver­
tical graticule lines.
3. W ithout making any adjustments to the oscilloscope,
move the signal probe from the input to the output o f the
device under test. If there is phase shift in the device, the
displayed waveform will be shifted horizontally.
4. Measure the amount of horizontal shift of the display
in centimeters.
5. Measure the distance in centimeters between corres­
ponding points on two consecutive cycles of the waveform.
6. Divide the measurement obtained in step 4 by the
measurement obtained in step 5 and multiply the result by
360°. This is the phase shift produced in the signal by the
device under test.
A second method for comparing the phase relationship
of two signals of the same frequency makes use of the X-Y
mode of operation (HORIZONTAL DISPLAY switch set to
HORIZ. AMPLIFIER, SWEEP DISABLED).
This method is
suitable only when comparing two sine waves.
1. Applying the sine waves to the two +INPUT connec­
tors. The display w ill be an ellipse. (Actually, the display
will appear as a diagonal straight line if the two sine
waves are inphase or exactly 180° out of phase, or it will
appear as a circle if the two sine waves are exactly 90°
or 2Z0° out of phase. Application of these instructions,
however, will still apply.)
2. Center the ellipse horizontally and vertically on the
CRT screen.
3. Measure the distances A and B on the display as shown
in Figure 2-8.
A /B is equal to the sine of the phase difference between
A
the two signals (Sin <j> = — ).
Fig. 2 -8 . X-Y method o f calculating phase difference ( 0 ) o f two
sine waves.
Direct Connection to the CRT Plates
In some applications it may be desirable to connect a
signal directly to one or both sets of CRT deflection plates,
bypassing the internal oscillscope amplifiers. The vertical
deflection plate pins are located on the side of the neck
of the CRT, and the horizontal deflection plate pins are
located at the bottom of the neck of the CRT.
W ith a signal connected directly to the CRT pins, it is
possible, under optimum impedance matching conditions and
with connections kept as short as possible, to obtain a band­
width on the order of 100 MHz with the Type 503. How­
ever, limitations of the sweep magnifier at the faster sweep
rates discussed earlier in this section must be kept in mind
when making risetime measurements on fast-rise wave­
forms. The vertical and horizontal deflection factors of the
CRT are approximately 20 volts per centimeter and 16 volts
per centimeter, respectively.
The diagram in Fig. 2-9 shows how a signal may be AC
coupled to the CRT deflection plates. This method of AC
coupling permits the use of front panel controls to position
the display on the screen. The SENSITIVITY control of the
bypassed am plifier should be placed in the 20 VOLTS/CM
position, and both INPUT switches should be placed in the
GND position. The value of the capacitors shown in Fig.
2-9 will depend upon the characteristics of the signal to be
displayed.
To DC couple a signal to the deflection plates, remove
the amplifier leads and connect the signal directly to the
CRT pins. Tape the ends of the loose am plifier leads to
prevent accidental shocks to operating personnel. For best
performance, the average of the voltages at the two plates
must be kept close to +1 5 0 volts: otherwise, the display
will be defocused and slightly bowed, and the sweep rate,
if the sweep is used, will not be accurate. Actually, if these
T,
2-9