For decades, temperature has been one of the most important process variables in the automation, consumer goods and production industries. Electrical measurement of temperature, by using resistance thermometers and thermocouples, is in fact more than 100 years old, but the develop-ment of sensors and thermometers is by no means over. The continuous optimization of processes
leads to ever higher demands on the thermometers, to measure temperature faster, more accurate-
ly, and with better repeatability over a longer time.
Since there is, regrettably, no single thermometer that is capable of handling all possible measure-
ment tasks with sufficient accuracy, it is vitally important, especially for the usen to be first familiar
with the fundamentals of electrical temperature measurement and then to understand the charac-
teristics and sources of error involved. A precision thermometer by itself is no guarantee that the
temperature will be properly measured. The temperature that is indicated is only the temperature of
the sensor. The user must take steps to ensure that the temperature of the sensor is indeed the
same as that of the medium being measured.
This book has been a favorite guide for interested users for many years. This version has been re-
vised and updated to take account of altered standards and new developments. In particular, the
new chapter Measurement uncertainty” presents the basic concepts of the internationally recog-
nized ISO guideline “Guide to the expression of uncertainty in measurement” (abbreviated to GUM)
and illustrates methods of determining the measurement uncertainty of a temperature measure-
ment system and the factors that affect it. The chapter on explosion-proof thermometers has also
been extended to take account of the European Directive 94/QIEC, which comes into force on
July 1st 2003.
In view of extended product liability, the data and material properties presented in this book can
only be considered to be guidelines. They must be checked, and corrected, if necessary, for each
individual application. This applies in particular where safety aspects are involved.