 Thermocouple reference junction

The thermocouple reference junction is the connection region where the two thermoelements meet the measurement leads. In ordinary copper-lead wiring there are two material transitions, A–Cu and B–Cu, rather than a second welded A–B junction. They must have a common known temperature $T_c$ for the simple expression $E(T_h,T_c)$ to apply. An ice-water heat bath can establish a nominal $0{}^{\circ }\mathrm{C}$ reference; cold-junction compensation instead measures $T_c$ locally. The word “cold” describes the reference role and imposes no requirement that $T_c<T_h$.