Tektronix 502A, Instruction Manual

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Operating Instructions — Type 502A
How to measure the ac component of a wave­
form
For measuring the ac component of a waveform, ac coup­
ling is normally used since it is usually not advantageous
to display the dc component of the waveform being mea­
sured. AC component voltage measurements can usually be
made with dc coupling also, but there is normally no par­
ticular advantage in doing so. To obtain peak-to-peak volt­
age measurement, perform the following steps.
1. To
use the graticule, measure the vertical distance in
centimeters from the level of the positive peak to the level of
the negative peak.
2. Multiply the setting of the SENSITIVITY Control by the
distance measured to obtain the indicated voltage.
3. Multiply the indicated voltage by the attenuation factor
of the probe you are using to obtain the true peak-to-peak
voltage.
Fig. 2-10. Voltage measurement of the ac component of a wave­
form. The vertical distance between peaks is multiplied by the
setting of the SENSITIVITY control and by the probe attenuation
factor to obtain the voltage measurement.
As
an example of this method, assume that using a 10X
probe and a sensitivity of 1 volt per centimeter, you mea­
sure a total vertical distance between peaks of 4 centimeters.
In this case then, 4 centimeters times 1 volt per centimeter
gives
you an indicated voltage of 4 volts peak-to-peak
of sine wave. The indicated voltage times the probe attenua­
tion factor of 10 then gives you the true peak-to-peak am­
plitude of 40 volts. The peak-to-peak sinusoidal voltage can
then be converted to peak, rms, or average voltage through
use of standard conversion factors.
How to measure instantaneous voltages
The method used to measure instantaneous voltages is
very similar to the method described previously for ac com­
ponent voltage measurements. A reference line must be es­
tablished on the c rt screen. The actual voltage measurement
is taken with respect to this reference line. If for example,
the voltage measurement is to be made with respect to
+1 00 volts, the reference line would correspond to +100
volts. In the following procedure the method is given for
establishing this reference line as ground since measurements
with respect to ground are by far the most common type
made. The same general method may be used to measure
voltage with
respect to any other potential, so long as that
potential is used to establish the reference line.
CAUTION
To prevent saturation of the vertical amplifiers,
the peak voltage to ground at any amplifier input
connector must not exceed 200 volts on 5, 10, and
20 VOLTS PER CM ranges; 20 volts on the .5, 1,
and 2 VOLTS PER CM ranges; and 2 volts on all
other ranges.
To obtain a voltage measurement with respect to ground,
perform the following steps:
1. To establish the reference line, DC couple the oscilloscope
input,
then touch the probe tip to the oscilloscope ground
terminal and rotate the TRIGGERING LEVEL Control fully
clockwise to the RECURRENT position.
Fig. 2-11. Measuring the instantaneous voltage. The vertical distance
from the point of measurement to a pre-established reference line
is multiplied by the setting of the SENSITIVITY control and by the
attenuation factor of the probe to obtain the voltage measurement.
2. Vertically position the trace to a convenient point on the
face of the crt. (This point will depend upon the polarity
and amplitude of the input signal, but it should always be
chosen so that the trace lies along one of the major divisions
of the graticule. The graticule division corresponding to the
position of the sweep is known as the ground reference line.
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