1.
Physical Basics
1.1 General Foreword
The following sections discuss temperature sensors that are brought into
direct contact with the medium to be measured. The (base and noble) thermocouple
assemblies and resistance thermometers described here are primarily used in
industrial temperature measurement technology. The information provided is
limited to the cited temperature sensors in standard configuration and to the
corresponding connecting cables. If the instrumentation is part of the scope of
delivery, additional information can be provided on request. The most important
data relating to temperature sensors, such as basic-value series and tolerances,
is defined in standards. Apart from the standard configurations described
here, RECKMANN GMBH also manufactures a wide variety of special
designs according to individual customer requirements.
1.2 Thermocouple Assemblies (TE)
Thermocouple assemblies exploit
the so-called Seebeck effect. If welding, soldering etc. is used to connect two
electrical conductors made of different metals at one end (measuring point) and this junction is heated,
a voltage (EMF or thermoelectric voltage) can be measured in
the mV range at the two free ends (reference junction). There must,
however, be a temperature difference between measuring point and
reference junction. Temperature measurement by means of thermocouple assemblies is therefore
based on a voltage measurement, the arising thermoelectric
voltage being a function of the temperature
difference between the measuring point and reference junction.
The amount of thermoelectric voltage, however, not only depends
on the above-mentioned temperature difference, but also on the
conductor materials used. The current range of metals and
alloys which guarantee a voltage curve without transition points and which constantly
increases with temperature, are used for industrial
measurements.
1.3 Resistance Thermometers (WT)
Resistance thermometers use the
constant change in resistance that
metals undergo when temperatures change. Owing to its high
stability and reproducibility, platinum is mainly used as a
resistance material. Nickel can also be used. Both
metals have a positive temperature coefficient (TC), i.e. their
resistance increases as the temperature rises.
Go to Section 2 (Thermocouple
Measuring Circle, Schematic
Diagram)
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