Temperature Detectors
THERMOCOUPLES
THERMOCOUPLES
The thermocouple is a device that converts thermal energy into electrical energy.
EO 1.4
DESCRIBE the basic construction of a thermocouple
including:
a.
Major component arrangement
b.
Materials used
EO 1.5
EXPLAIN how a thermocouple provides an output
representative of the measured temperature.
Thermocouple Construction
Figure 4 Thermocouple Material Characteristics
When Used with Platinum
A thermocouple is constructed of
two dissimilar metal wires joined
at one end. When one end of each
wire is connected to a measuring
instrument,
the
thermocouple
becomes a sensitive and highly
accurate
measuring
device.
Thermocouples may be constructed
of several different combinations
of materials. The performance of
a
thermocouple
material
is
generally determined by using that
material with platinum. The most
important factor to be considered
when selecting a pair of materials
is the "thermoelectric difference"
between the two materials.
A
significant difference between the
two materials will result in better
thermocouple performance. Figure 4 illustrates the characteristics of the more commonly used
materials when used with platinum.
Other materials may be used in addition to those shown in Figure 4. For example: Chromel-
Constantan is excellent for temperatures up to 2000°F; Nickel/Nickel-Molybdenum sometimes
replaces Chromel-Alumel; and Tungsten-Rhenium is used for temperatures up to 5000°F. Some
combinations used for specialized applications are Chromel-White Gold, Molybdenum-Tungsten,
Tungsten-Iridium, and Iridium/Iridium-Rhodium.
Rev. 0
Page 5
IC-01
