|
| |
TM 9-254
8-6.
Waveform Reading - Continued
(6)
One complete cycle should be displayed on the CRT (fig. 8-14). Before you can calculate the frequency,
you must first compute the time duration of one complete cycle. Count the number of divisions of
horizontal deflection for one complete cycle and use the following formula to determine frequency.
TIME DURATION =
(HORIZONTAL DEFLECTION)
X
(HORIZONTAL SWEEP)
(IN DIVISIONS FOR 1 CYCLE)
(SETTING IN SECONDS)
EXAMPLE:
TIME DURATION = (10 DIVISIONS) X (.1 MILLISECONDS PER DIVISIONS)
TIME DURATION = 1.0 MILLISECONDS
To determine the frequency, use the following formula:
1
=
1
TIME DURATION
.001
(IN SECONDS)
8-7.
Oscilloscope Probes.
a.
General. When a waveform is to be analyzed, a probe may be used. Most probes have more than one tip
which can be inserted on the end of the probe, figure 8-15. These tips may be changed by unscrewing them from the end
of the probe and screwing the desired tip in place. A ground strap is also supplied with the probe. The spring clip of the
grounding strap clamps over the bared portion of cable at the upper end of the probe. The other end of the ground strap
uses an alligator clip for connection to chassis ground of the equipment under test. This completes the ground connection
between equipment under test and the oscilloscope.
b.
Attenuation Factor. A probe may have an attenuation factor of ten or one hundred. The signal amplitude is
reduced by the attenuation factor of the probe. This is done to allow for the measurement of signal amplitudes which
exceeds the rated input capability of the vertical amplifier input channel. When using a probe which has attenuation, an
additional step must be added to the procedure for computing the voltage:
(1)
Count the number of divisions of vertical deflection.
(2)
Multiply number of divisions by the setting of the VOLT/DIV switch (2, fig. 8-9).
(3)
Multiply the results of step (2) above by the attenuation factor of the probe. The result equals the peak-
to-peak voltage of the displayed signal.
c.
Probe Calibration (fig. 8-16). When a probe is used with an oscilloscope for the first time or when it is
transferred from one plug in unit to another, the probe must be adjusted or calibrated. This will insure accurate attenuation
of signals. Calibrate the probe as follows:
FREQUENCY =
(IN HERTZ)
.= 1000Hz
8-21
|
