THERMOCOUPLE CORRECTIONS FROM IRREVERSIBILITY THEORY.
Technical summary rept.,
MATHEMATICS RESEARCH CENTER UNIV OF WISCONSIN MADISON
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The resultant error introduced by using finite impedance measuring instruments in thermocouple circuits was determined quantitatively and rigorously. The standard-practice correction formula to account for finite impedance of measuring instruments in thermocouple circuits is valid provided there are no excessive radial temperature and voltage gradients. The measured voltage can be corrected to give voltage values for use with standard tables. The analysis shows that error is reduced by decreased thermocouple circuit resistance RTC including all lead wires and increased instrument impedance internal impedance of instrument alone. The effect of the temperature dependence of the electrical conductivity and the absolute thermoelectric power are exactly accounted for by an equation which requires that the total resistance RTC, which is dependent upon the temperature variation along the wires, be determined. A procedure was also indicated that minimizes the effect of unequal lead-wire junction temperatures.
- Test Facilities, Equipment and Methods