Thermoelectric transducers elements convert the change of measurand (temperatures) into the change of current, arising up because of difference of temperature on the junction of two heterogeneous materials, which an effect of Seebeck (fig. 17) is in. A thermoelectric transducers is anymore known under the name thermocouples, in which a probe consists of two junctions, one of which takes place in a point, where taking temperature is produced, and second - in the point of supporting temperature (fig. 18). Difference of potentials of V1 - V2 which appears on two junction (known as pin potentials), depends on the temperature of shuts and measured by a voltmeter. Thus, the testimonies of voltmeter represent the difference of temperatures between junction.
Fig. 17. Effect of Seebeck, at which in a chart, consisting of shuts of two heterogeneous metals, being at a different temperature, there is a current
Fig. 18. Principle, actions of thermocouple
Fig. 19. Typical dependences of tension on the difference of temperature for thermocouples the junctions of which are executed from different materials : 1 is a nickel-chrome/constantan (Е); 2 is iron/constantan (type of J), 3 is a copper/constantan (type of Т); 4 is a nickel-chrome/a nickel-manganese is aluminium-silicon (type of К); 5 platinum-rhodium/platinum (type of R) 6 is platinum-rhodium/platinum (type of S)
On a fig. 19 the tensions crooked, characterizing dependence are shown from the difference of temperatures for the row of typical materials which the junctions of thermocouples appear from. Although these dependences seem linear, the detailed researches show that it not quite so. In practice not so it is simple to attain necessary exactness of the temperature measuring by means of thermocouples, as it can appear from reasonings given above, as connection of voltmeter with a thermoelectric chart self on itself forms a new...