Tektronix 502A, Instruction Manual

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Operating Instructions — Type 502A
(Do not adjust the vertical positioning control after this
reference point has been established.)
3. Remove the probe tip from ground and connect the probe
to the signal source. Adjust the TRIGGERING LEVEL Control
for a stable display.
4. Measure the vertical distance in centimeters from the
point to be measured to the ground reference line by use of
the graticule.
5. Multiply the setting of the SENSITIVITY Control by the
distance measured to obtain the indicated voltage.
6. Multiply the indicated voltage by the attenuation factor
of the probe you are using to obtain the true voltage with
respect to ground.
As an example of this method, assume that you are us­
ing a 10X probe and a sensitivity of .2 volts per centimeter
and that after setting the reference line at the bottom of the
graticule, you measure a distance of 8 centimeters to the
point you wish to measure. In this case then, 8 centimeters
times .2 volts per centimeter gives you an indicated voltage
of 1.6 volts. Since the voltage point is above the ground
reference line, the polarity is indicated to be positive. The
indicated voltage times the probe attenuation foctor of 10
then gives you the true voltage of positive 16 volts.
You should remember in determining the polarity of
voltages measured in this fashion that inputs applied to
the B input connectors are inverted on the face of the crt.
Consequently, the apparent polarity of these inputs is op­
posite the true polarity. To prevent possible confusion as
to polarity it is usually best to use the A input connectors
for voltage measurements with respect to ground.
Time Measurement
Accurate elapsed time or time interval measurements
can be made by utilizing the calibrated timebase feature
of the Type 502A Oscilloscope. The sweeps are calibrated
so that the beams are deflected across the screen at known
rates. Since the beam travels completely across the screen
in a known period of time, the time required for the beam to
travel any portion of the distance can be determined. By
measuring the horizontal distance between points on the
displayed waveform, and by knowing the sweep rates, you
can determine the time interval between the two points.
For accurate measurements be sure the same reference point
is used on both pulses and the VARIABLE TIME/CM Control
is in the CALIBRATED position. The method for measuring a
time interval is as
follows:
1. Using the graticule, measure the horizontal distance
in centimeters between two points whose time interval you
wish to find.
2. Multiply the distance measured by the setting of the
TIME/CM control to obtain the apparent time interval.
3. Divide the apparent time interval by the magnification
indicated
by the setting of the HORIZONTAL DISPLAY switch
to obtain the correct time interval.
Frequency Measurement
The frequency of a periodically recurrent waveform can be
determined if the time interval (period) of one complete
Fig. 2-12. Measuring the time interval (period) of one complete
cycle of a periodically recurrent waveform. The horizontal distance
in centimeters of one complete cycle (in this case 3 centimeters) is
multiplied by the setting of the TIME/CM control and is divided
by the sweep magnification to obtain the time interval. The fre­
quency of the waveform is the reciprocal of its time interval.
cycle of the waveform is known. This time interval can be
measured by means of the procedure described in the preced­
ing paragraph. The frequency of a waveform is the recipro­
cal of its
time interval
Using DC BAL and FINDER Controls
It is best to disconnect the input signal, unless the
approximate amplitude of it is known. If the amplitude of
the input signal is known then set the SENSITIVITY Control
for a crt display of two or three centimeters and follow
the instructions for no input signal.
With no input signal, turn the TRIGGERING LEVEL to
RECURRENT, the single sweep MODE switch to NORMAL
and the INTENSITY Control to a reasonable level. The above
control settings are to insure that a trace can be seen, when
it is found.
Set the vertical POSITION Control of the proper beam to
its midrange position. With the SENSITIVITY Control in the
.2 VOLTS PER CM position. If no input signal is connected to
the Type 502A, change the SENSITIVITY Control to the .1 m
VOLTS PER CM position and depress the FINDER Button. The
trace should now be seen on the crt. Now turn DC BAL
Control in either direction until a "fast area” is seen. A 'fast
area”
is an area of the DC BAL Control where the trace will
move a large distance for a very small movement of the DC
BAL Control.
When the "fast area" of the DC BAL Control is found,
the trace should be positioned in the center of this area
with the DC BAL Control. The FINDER Button may now be
released and the trace positioned to the proper place on
the graticule.
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