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TM 9-254
8-3.
Multimeter Familiarization - Continued
f.
Test Leads (fig. 8-5). Each instrument is furnished with one pair of four-foot test leads. One lead is black
and the other is red for easy polarity identification. The insulation property of the test leads is a special high-grade rubber
which has far more insulation strength than the largest voltage for which the instrument is rated.
8-4.
Scale Interpretation.
a.
Ohms Scale (fig. 8-6). This scale is a nonlinear scale used only for the purpose of reading resistance. Zero
ohms is at the right end of the scale and moving across the scale to the left, the divisions become closer together. The
extreme left end of the scale is marked infinity (). This represents a resistance beyond the range of the meter. It should
be pointed out that for the purpose of accuracy, a range should be selected on the meter that will produce a pointer
indication on the right-half of the ohms scale. The reason is obvious when observing the numbers on the right-half of the
ohms scale. The numbers are spaced further apart with more graduations in-between the numbers, allowing for a more
accurate reading.
b.
DC Voltage Scales (fig. 8-6). The black scale, located directly beneath the ohms scale, is a linear scale used
to measure +DC and -DC voltages and direct current. The scale divisions are equally spaced and start at the left with 0
and end at the right with 250. For the 2.5V range, use the 0-250 figures and divide by 100. For the 10V, 50V, and 250V
ranges simply read the figures directly from the scale. For the 1000V range, use the 0-10 V range and multiply the
readings by 100. For the 5000V range use the 0-50V range and multiply the reading by 100.
c.
AC Voltage Scales (fig. 8-6). The root-mean-square (RMS) value of an AC voltage is measured on the red
scale directly beneath the black DC scales. For the 0-2.5V range, read the value directly on the scale marked 2.5VAC
only. For the 20V, 50V, and 250V ranges, read the red scale marked AC but use the black figures immediately above the
red scale. For the 1000V range, read the red scale marked AC using the black 0-10 V range and multiply the reading by
100. For the 5000V range, read the red scale marked AC using the black 0-50 V range and multiply the reading by 100.
d.
DB Scale (fig. 8-6). For some applications, output voltage and audio frequency voltage are frequently
measured in terms of decibels. The decibel (DB) scale located at the bottom of the meter face is numbered from -20
through 0 and up to +10. For the 10V range, read the DB scale and add +12DB to the reading. For the 50V range, read
the DB scale and add +26DB to the reading. For the 250V range, read the DB scale and add +40DB to the reading.
Figure 8-6. Multimeter Face
8-10
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