Thermocouples will cause an electric current
to flow in the attached circuit when subjected to changes in
temperature. The amount of current that will be produced is
dependent on the temperature difference between the
measurement and reference junction; the characteristics of
the two metals used; and the characteristics of the attached
circuit. The illustration below a simple thermocouple circuit.
Simple Thermocouple Circuit
Heating the measuring thermocouple produces a
voltage which is greater than the voltage across the
reference junction. The difference between the two voltages
is proportional to the difference in temperature
and can be measured on the voltmeter (in millivolts). For
ease of operator use, some voltmeters are set up to read out
directly in temperature through use of electronic circuity.
Other applications provide only the millivolt
readout. In order to convert the millivolt reading to its
corresponding temperature, you must refer to tables like the
one shown below. These tables can be obtained from the
thermocouple manufacturer, and they list the specific
temperature corresponding to a series of millivolt readings.
