VOLTAGE MEASUREMENT
Accurate voltage measurements of inputs to
the vertical amplifiers can be made using the
calibrated deflection factor feature of the Type
502. The following instructions tell you how to
use the oscilloscope for this purpose and how to
obtain the greatest possible accuracy in your
measurements. It is important that proper tech
niques be used in order that errors are not in
troduced in the results.
During voltage measurements, you should al
ways display the waveform across as much of
the crt face as is possible since, as a general
rule, the accuracy of your measurements will in
crease as the vertical size of the displayed
waveform is increased. In measuring voltages,
it is important to remember that the width of the
trace may be appreciable part of the overall
measurement and care should be used that the
trace width is not included in the vertical deflec
tion readings that you obtain. You should con
sistently make all your readings from one side of
the trace. If the bottom side of the trace is used
for one reading, it should be used for all suc
ceeding readings.
How to measure the ac component of a
waveform.
For measuring the ac component of a wave
form, ac coupling is normally used since it is
usually not advantageous to display the dc com
ponent of the waveform being measured. AC
component voltage measurements can usually be
made with dc coupling also, but there is nor
mally no particular advantage in doing so. To
obtain peak-to-peak voltage measurement, per
form the following steps:
1. Through the use of 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 con
trol by the distance measured to obtain the in
dicated voltage.
3. Multiply the indicated voltage by the atten
uation factor of the probe you are using to
obtain the true peak-to-peak voltage.
As an example of this method, assume that
using a 10X probe and a sensitivity of 1 volt per
centimeter, you measure a total vertical distance
between peaks of 4 centimeters. In this case
then, 4 centimeters times 1 volt per centimeter
Fig. 3-6. Voltage measurement of the ac component of
a waveform.
The vertical distance between peaks is multiplied by
the setting of the SENSITIVITY control and by the
probe attenuation factor to obtain the voltage meas
urement.
gives you an indicated voltage of 4 volts peak-
to-peak. The indicated voltage times the probes
attenuation factor of 10 then gives you the true
peak-to-peak amplitude 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 component voltage measure
ments except that for instantaneous voltage
measurements, a reference line must be esta
blished on the crt screen. The actual voltage
measurement is taken with respect to this refer
ence line. If, for example, the voltage measure
ment is to be made with respect to -{-100 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 meas
ure voltage with respect to any other potential,
however, so long as that potential is used to es
tablish the reference line.
OPERATING INSTRUCTIONS — TYPE 502
3-7
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