Effect of Pressure on emf of Thermocouples

Abstract

``Pressure'' thermal emf's have been measured for constantan, Pt, Ni, alumel, Pt 10% Rh, Cu, chromel, and Ni 18% Mo for a ΔT of 100°C over a pressure range 0 to 72 kbar. Corrections due to pressure for common thermocouples made of pairs of these metals have been deduced. A number of thermocouple pairs have been compared at temperatures up to 1200°C and pressures up to 58 kbar. Below 200 to 300° the deviations between them agree quite well with the absolute data on single metals taken at ΔT of 100°C. At higher temperatures the deviations diminish and generally reverse. It appears that the deviation δT of the readings of two thermocouples at a given pressure follow roughly the relationship δT = A (P)ΔT+B(P)ΔT², where ΔT is the temperature interval in the pressurized zone, A (P) and B (P) are functions of pressure (roughly linear), and B (P) is generally opposite in sign to A (P) and is large enough to dominate the A (P) term at higher ΔT's.