Calibrating of thermocouple

   If it is needed calibration thermocouple (id est to set dependence of thermo-electromotive force on the difference of temperatures of shuts of thermocouple) that it can be done, for example, as follows.
   The simple experimental setting from which is clear essence of methods of calibrating is represented on a fig. 1. One shut of thermocouple (for example a copper () is a constantan ()) is submerged in a vessel with butter (temperature of ), other in a vessel with ice To =0 . Because calibration charts over in literature are brought in relation to 0 , then the best of all to adhere to this condition, because in future it is possible it will be easily to compare the got experimental results to tabular.  In addition melting ice  enables simply enough and exactly to fix one of temperatures in relation to which calibrating, and afterwards measuring is executed by means of this thermocouple. A vessel with butter is heated by an electric heater , and T taken temperature by the thermometer of t of necessary exactness. Arising up as a result of one heating of shuts of thermocouple thermo - E.M.F, measure by means of potentiometer of direct-current. We make a table or build the chart of dependence E.M.F from the temperature of .
   If high exactness of calibrating and measuring is not needed, then it is possible to calibrate in relation to a room temperature. In this case the second shut can be placed in butter, being at a room temperature (That approximately 20 ).

Fig. 1:

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Calibrating of thermocouple
Thermoelectricity - brief theory.
In a chain composed of two or more dissimilar metals or semiconductors, temperature gradients cause the appearance of electromotive forces. Electro-moving forces arise due to the thermal motion of free electrons (or holes) in the contacts of dissimilar conductors, as well as in the conductors themselves. This phenomenon is called thermoelectricity, and the resulting EMF is called thermoelectric power (thermopower).

The quantity theory of thermoelectric phenomena can only be built on the basis of quantum mechanics; within classical physics it is possible to identify only rough qualitative picture, allowing to visualize the causes of the thermopower, but not giving consent to experience often, even in order of magnitude.

On the boundary of two conductors A and B due to thermal motion arise counter flow of electrons. If the number of electrons per unit volume of each conductor is different, say nA > nB, then the flux from A to B will be more intense than from B to A , and the number of electrons in B will begin to increase. This will reduce the potential of conductor B, and the resulting potential difference will align the electronic flows. There is a potential difference of UA - UB, which will be established when the equilibrium is reached.