# IEC 60027-3:2002 pdf download

IEC 60027-3:2002 pdf download.Letter symbols to be used in electrical technology – Part 3:Logarithmic and related quantities, and their units.

b) logarithmic quantities. In which the argument is given explicitly as a number, for example ?ogarithmvc information-theory quantifies, such as decision content, where the argument is a number of mutually exclusive events, and information content, where the argument Is the reciprocal of a probability:

c) other logarithmic quantities.

In the set of logarithmic and related quantities there are also included quantities which are a

linear combination of logarithmic quantities, or a derivative of a logarithmic quantity, or a

quotient of a logarithmic quantity and another quantity, for example attenuation coefficient.

The logarithm to any specified base of an argument gives the same Information about the situation under consideration, as does the argument Itself. Ouantlties defined with logarithms of different bases are proportional to each other, but have different values and thus are different quantities. In a given field of application, only logarithms of one base shall be used to define logarithmic quantities. Because of the proportionality between the logarithms It Is possible to express the numerical values using different bases of the logarithm together with different units. To avoid ambiguities In applications the unit shall be written Out explicitly after the numerical value in a logarithmic quantity.

NOTE I in ihis patt of EC 60027. complex quanhhel are denotd by underiininç thsir cymbols However, this does not constitule a coenpuisory rule in applications see iEC 60027-1)

4 LogarithmIc ratios of f.Id quantities and power quantities

4.1 Logarithmic ratios of field quantities

A quantity the square of which is proportional to power when It acts on a linear system is here called a field quantity, general symbol I-.

EXAMPLES

Electric current, voltage, electric field strength, sound pressure, particle speed. and force are field quantities.

For sinusoidal time-varying field quantities, the ratio of the amplitudes or the root-mean- square values is the argument of the logarithm.

For non-sinusoidal field quantities, the root-mean-square value over an appropriate time interval to be specified is used. For a periodic quantity, the appropriate time interval is the periodic time.

For logarithmic ratios of field quantities, logarithms with two different bases are used for the numerical values. These logarithms are:

— natural logarithm, symbol In (or loge).

— decimal logarithm, symbol Ig (or log10).

For real field quantity ratios, F11F2, the following general expressions of a logarithmic ratio, Q. expressed in different units are obtained:

6 Other logarithmic quantities

6.1

General

There are other logarithmic quantities than logarithmic ratios of field or power quantities, and

logarithmic information-theory quantities,

EXAMPLES

Logarithmic frequency interval, optical density, pH.

The units neper (Np) and bel (B), or its sub-mutiple decibel (dB)，shall not be used when a relation between the quantity considered and a field quantity or a power quantity does not exist.

The units shannon (Sh), natural unit of information (nat), and harley (Hart), shall be used only in information theory.

6.2

Logarithmic frequency interval

For logarithmic frequency interval, logarithms with two different bases are used for the

numerical value. These logarithms are:

binary logarithm, symbol Ib (or log2).

decimal logarithm, symbol Ig (or 10910)-

For logarithmic frequency interval, the fllowing general expressions expressed in different units are obtained:

With the quantity G defined by convention with the binary logarithm,

which is the practice in acoustics, the octave, symbol oct, becomes the coherent unit which can be replaced with one, symbol 1 (see ISO 31-7.7-3).

7 Names, symbols, and definitions

Names, symbols, and definitions of logarithmic quantities, and their units in electrical technology, are given in other parts of IEC 60027. mainly in part 2. Names, symbols, and definitions of logarithmic quantities, and their units in information theory are given in ISO/IEC 2382-16.