Power Measurement Fundamentals 11
Table 1-5. Prefixes of Large Units
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Prefix Abbreviation Number of Times Larger than 1
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Kilo k 1000
Mega M 1,000,000
Giga G 1,000,000,000
——————————————————————————————Large Units
Sometimes electrical measurements are very large, such as 20,000,000
W, 50,000, or 38,000 V. When this occurs, prefixes are used to make these
numbers more manageable. Some prefixes used for large electrical values
are shown in Table 1-5. To change a large value to a smaller unit, divide
the large value by the value of the prefix. For example, 48,000,000 Ω is
changed to 48 megohms (MΩ) by dividing by one million: 48,000,000 Ω
÷ 1,000,000 48 MΩ. To convert 7000 V to 7 kilovolts (kV), divide by one
thousand: 7000 V ÷ 1000 = 7kv. To change a large value to a unit with a
prefix, move the decimal point in the large value to the left by the number
of zeros represented by the prefix. Thus 3600 V equals 3.6 kV ( 3 6 0 0 ).
To convert a unit with a prefix back to a standard unit, the decimal point
is moved to the right by the same number of places in the unit, or, the
number may be multiplied by the value of the prefix. To convert 90 MΩ to
ohms, the decimal point is moved six places to the right (90,000,000). The
90 MΩ value may also be multiplied by the value of the prefix, which is
1,000,000. Thus 90 MΩ × 1,000,000 = 90,000,000 Ω.
The simple conversion scale shown in Figure 1-1 is useful when con-
verting standard units to units of measurement with prefixes. This scale
uses either powers of 10 or decimals to express the units.SCIENTIFIC NOTATION
Using scientific notation greatly simplifies arithmetic operations. Any
number written as a multiple of a power of 10 and a number between 1
and 10 is said to be expressed in scientific notation. For example:81,000,000 = 8.1 × 10,000,000, or 8.1 × 107
500,000,000 = 5 × 100,000,000, or 5 × 108
0.0000000004 = 4 × 0.0000000001, or 4 × 10 –10) ) ) )