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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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