Tektronix 422, Instruction Manual

Page: 32 / 213

OperatingInstructions—Type 422 AC-DC
Instantaneous Voltage Measurements-DC
To measure the DC level at a given point on a waveform,
use the follow ing procedure:
1. Connect the signal to either INPUT connector.
2. Set the vertical Mode switch to display the channel
used.
3. Set the VO LTS/DIV switch to display about six divis­
ions of the waveform.
4. Set the input Coupling switch to GND.
5. Set the TRIGGERING Mode switch to AUTO.
10. Establish the polarity o f the signal. If the waveform
is above the reference line the voltage is positive; below the
line, negative (with the INVERT switch pushed in fo r Chan­
nel 2).
11. M ultiply the distance measured in step 9 by the
VO LTS/D IV switch setting. Include the attenuation factor
of the probe, if used.
EXAMPLE: Assume that the vertical distance measured
is 4.6 divisions (see Fig. 2-15) and the waveform is above
the reference line using a 10X attenuator probe and a
VOLTS/DI V switch setting o f 2.
Using the formula:
6. Position the trace to the bottom line o f the graticule
or other reference line. If the voltage is negative w ith re­
spect to ground, position the trace to the top line of the
graticule. Do not move the vertical POSITION control after
this reference line has been established.
NOTE
To measure a voltage level w ith respect to a voltage
other than ground, make the follow ing changes in
step 6. Set the Input Coupling switch to DC and ap­
ply the reference voltage to the INPUT connector.
Then position the trace to the reference line.
Instantaneous
Voltage
vertical
distance X polarity X
(divisions)
VO LTS/DIV
setting
probe
X attenuation
factor
Substituting the given values:
Instantaneous
Voltage
4.6 X +1 X 2 V X 10
7. Set the Input Coupling switch to DC. The ground
reference line can be checked at any tim e by switching to
the GND position.
8. Set the TRIGGERING control to obtain a stable dis­
play. Set the T IM E /D IV switch to a setting that displays
several cycles of the signal.
9: Measure the distance in divisions between the refer­
ence line and the point on the waveform at which the DC
level is to be measured. For example, in Fig. 2-15 the meas­
urement is made between the reference line and point A.
Fig. 2-15. Measuring instantaneous DC voltage with respect to a
reference voltage.
The instantaneous voltage is +92 volts.
Comparison Measurements
In some applications it may be desirable to establish
arbitrary units o f measurement other than those indicated
by the V O LTS/D IV switch or T IM E /D IV switch. This is
particularly useful when comparing unknown signals to a
reference amplitude or repetition rate. One use fo r the
comparison-measurement technique is to facilitate calibra­
tion o f equipment (e.g., on an assembly-line test) where the
desired amplitude or repetition rate does not produce an
exact number of divisions of deflection. The adjustment
w ill be easier and more accurate if arbitrary units o f meas­
urement are established so that correct adjustment is indica­
ted by an exact number o f divisions of deflection. A rb itra ry
sweep rates can be useful fo r comparing harmonic signals to
a fundamental frequency, or fo r comparing the repetition
rate of the input and output pulses in a digital count-down
circuit. The follow ing procedure describes how to establish
arbitrary units of measure fo r comparison measurements.
Although the procedure fo r establishing vertical and hori­
zontal arbitrary units o f measurement is much the same,
both processes are described in detail.
Vertical Deflection Factor. To establish an arbitrary
vertical deflection factor based upon a specific reference
amplitude, proceed as follows:
1. Connect the reference signal to the INPUT connector.
Set the T IM E /D IV switch to display several cycles o f the
signal.
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