•
To facilitate the reading of numbers with many digits, the digits may be sepa-
rated into groups of three counting from the decimal point. The groups should be
separated by a space, never a comma, which may be confused for a decimal point.
Use of prefixes for symbols
•
The most commonly used prefixes are given in Table 1.7.
•
When joining a prefix and SI unit symbol, there is no space between the prefix
symbol and the unit symbol, e.g. 10 mK or 10 m
°
C, not 10 m K.
1.6 Documentary Standards
From a traceability perspective the most important contribution of documentary standards to the rmometry is in the area of test methods. There are very few properties of
materials that do not change with temperature, and consequently a very high percentage
of test methods involve the measurement of temperature.
Documentary standards also cover a number of aspects of interest to thermometrists,
including:
•
Specifications for the response of platinum resistance thermometers and thermo-
couples, and the dimensions and scales for liquid-in-glass thermometers.
•
Colour codes for thermocouple lead wires, and colours and dimensions of thermo-
couple plugs and sockets.
•
The materials and dimensions for sheathing materials and thermowells (the protec-
tive pockets used for mounting thermocouples in industrial plants).
•
Dimensional and electrical specifications for industrial instrumentation such as
temperature controllers.
•
Specifications for furnaces and ovens, especially those used for heat treatment and
sterilisation.
•
Electrical and communication standards for instrument interfaces.
•
Quality assurance and laboratory accreditation systems.
A short summary of major standards organisations relevant to thermometry is given in
Table 1.8.
It is notable that only a few of the standards organisations are truly international.
Consequently, there may be differences between standards from different organisa-
tions, apparently for the same device or protocol. Particular examples include the
standards for platinum resistance thermometers and thermocouples, where there are
small differences. As the standards have been revised following the change to the
ITS-90 temperature scale, many of the standards have become harmonised.
It is beyond the scope of this book to catalogue all of the temperature-related
standards available from these organisations. Your local standards organisations will
have catalogues available and may be able to advise which standards are relevant. In
addition, most of the organisations now have Internet sites, with good search engines
and on-line shops. Many of the organisations also have application guides and manuals