Tektronix 585 - Page 23

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OOCO
SECTION 3
APPLICATIONS
General
Oscilloscopes are used principally as aids to instrument
calibration and for waveform observations in research or
new circuit design. Electronic engineers continue to reach
into the higher frequencies with greater ease through re 
search of solid state materials, and by the increased band 
pass and sensitivity of modern oscilloscopes.
Your Tektronix Type 585 Oscilloscope with Type 80/P80
or Type 82 Plug-In Unit systems, offers basic 100 millivolt
sensitivities, with a 3 db response of approximately 95 mega 
cycles, permitting accurate measurements of high frequency,
low level signals.
A versatile group of oscilloscope cameras for making per 
manent records of your waveform observations is presented
in the Accessories section of this manual.
Voltage Measurements
The Type 585 Oscilloscope can be used to measure the
voltage of the input waveform by using the calibrated
vertical-deflection factors of the instrument and associated
plug-in unit. The method used for all voltage measurements
is basically the same although the actual techniques vary
somewhat depending on the type of voltage measurements:
ac-component voltage measurements and instantaneous volt 
age measurements with respect to some reference potential.
Many waveforms contain both ac and d c voltage com 
ponents. It is often necessary to measure one or both of
these components, (see Figure 3-1).
Fig. 3-1. Typical waveform applied to the oscilloscope. Shown are
the ac component, de component, and instantaneous voltage of the
waveform.
When making accurate voltage measurements, display
the vertical waveform over only the center two centimeters
of the graticule for maximum accuracy, avoiding the bottom
centimeter where compression is greatest. Also, it is im 
portant not to include the width of the trace in your meas 
urements. You should consistently make all measurements
from one side of the trace. If the bottom side of the trace
is used for one reading, it should be used for all succeeding
readings.
When using the Type 81 Plug-In Adapter, the letter series
plug-in unit VARIABLE VOLTS/CM control must be in the
CALIBRATED position.
AC Component Voltage Measurements
In Oscilloscope measurements, the ac component of a
waveform is usually measured in terms of its peak-to-peak
or peak-to-trough value. This type of measurement is most
conveniently made by using the graticule to measure the
vertical distance between peaks and multiplying this distance
by the deflection factor of the oscilloscope. The figure
obtained is the actual peak-to-peak voltage. In most cases,
the ac component of a waveform can be measured with
the probe Input Selector switch in either the AC or DC posi 
tion. It may be necessary to use the AC position however,
in certain applications to prevent the d c component of the
waveform from deflecting the trace off the screen. Also
to prevent inaccuracies, the DC position should be used
when low-frequency measurements are made.
To make a peak-to-peak voltage measurement on the ac
component of a waveform, the following method can be
used (see Figure 3-2):
1. With the aid of the graticule, measure the vertical dis 
tance in centimeters from the positive peak to the negative
peak.
2. Multiply the vertical distance between peaks by the
vertical sensitivity per centimeter to obtain the indicated
voltage.
3. Multiply the indicated voltage by the attenuation factor
of any probe or attenuator used to obtain the actual peak-
to-peak voltage.
As an example, assume that when using the P80 Probe
with a 5-1 attenuator you measure a vertical distance be 
tween peaks of 2.1 centimeters. In this case then, 2.1 centi 
meters multiplied by 0.1 volt per centimeter gives 0.21 volt.
This figure multiplied by the attenuation factor of 5 gives
the actual peak-to-peak voltage, 1.05 volts.
3-1