dissimilar metal conductors are connected
together to form a closed circuit
and the two junctions are kept in
different temperatures, thermal electromotive
force(EMF) is generated in the circuit(Seebeck's
one end(cold junction)is kept constant
at a certain temperature, normally
at 0, and the other end(measuring
junction)is exposed to unknown temperature,
the temperature at latter end can
be determined by measurement of EMF
so generated. This combination of
two dissimilar metal conductors are
in comparison with other thermometers,
have the following features.
and comparatively small tome-lag.
2.If appropriate selection of a quality
thermocouple is made, a wide range
of temperature from absolute 0 to
2,300"C can be measured.
3.Temperature of specific spot or
small space can be measured.
4.Since temperature is detected by
means of EMF, measurement, adjustment,
amplification, control, conversion
and other data processings are easy.
5.Less expensive and easily available
in comparison with other temperature
and Measuring Method
industrial thermocouple is inserted
into an insulating tube to prevent
short circuit between the element
wires and then inserted into a protective
tube so as not to contact directly
the object or surrounding atmosphere.
Reference junction is compensated
at a certain temperature(mostly at
0"C) for measurement. T he EMF
so generated is measured by means
of moving coil type, electronic type,
auto-balancing type, potentiometric
or other indicating instruments.
Precautions in Practical Applications
are various types of thermocouples,
it is most important to select the
appropriate thermocouple for the specific
application, In addition, care should
be given to the selection of protection
tube, structure and fitting method
with due consideration of resistance
to heat, corrosion and vibration.