A thermocouple is a temperature measuring device consisting of two
conductors of dissimilar metals or alloys that are connected only
at the ends. When the ends are at different temperatures a small
voltage is produced in the wire that can be related directly to the
temperature difference between the ends. If the temperature at one
end is known, the temperature at the other end can be determined.
Thermocouple wire or extension grade wire is recommended to be used
to connect thermocouples to the sensing or control instrumentation.
The conditions of measurement determine the type of thermocouple
wire and insulation to be used. Temperature range, environment,
insulation requirements, response, and service life should be
Calibration Type Characteristics
Normal Operating Temperatures (°F)
Iron (JP)/ Constantan(JN)
TYPE J(Iron vs Constantan) is used in vacuum, oxidizing, inert or
reducing atmospheres. Iron element oxidizes rapidly at temperatures
exceeding 538'C, and therefore heavier gauge wire is recommended
for longer life at these temperatures.
TYPE K(CHROMEL vs ALUMEL ) is used in oxidizing, inert or dry reducing
atmospheres. Exposure to vacuum limited to short time periods. Must
be protected from sulfurous and marginally oxidizing atmospheres.
Reliable and accurate at high temperatures.
TYPE T(Copper vs Constantan) is used or service in oxidizing, inert or
reducing atmospheres or in vacuum. It is highly resistant to
corrosion from atmospheric moisture and condensation and exhibits
high stability at low temperatures. It is the only type with limits
of error guaranteed for cryogenic temperatures.
TYPE E(CHROMEL vs Constantan) may be used in oxidizing, inert or dry
reducing atmospheres, or for short periods of time under vacuum.
Must be protected from sulfurous and marginally
oxidizingatmospheres. Produces the highest EMF per degree o any