= Isothermal terminal block
An <isothermal terminal block> keeps the two reference transitions and the reference <thermometer> at approximately the same <temperature>, while maintaining electrical insulation between the terminals. Thermal contact is required; an electrical short between A and B would bypass the signal. Merely using <copper> does not eliminate the <Seebeck effect> in the meter leads. If both homogeneous <copper> leads start at $T_c$ and end at a common meter-input <temperature> $T_m$, their contributions have equal magnitude and opposite sign around the measurement path:
$$
\int_{T_c}^{T_m}S_{\rm Cu}(T)\,dT-\int_{T_c}^{T_m}S_{\rm Cu}(T)\,dT=0.
$$
This cancellation uses matched endpoint <temperatures> and homogeneous lead material, rather than $S_{\rm Cu}=0$. A <temperature gradient> along each lead is allowed under these assumptions. If the two transitions are at different <temperatures>, one measured $T_c$ cannot generally correct both; unmatched connectors or wire inhomogeneity can introduce additional <electromotive forces>. The FP-TC-120 documentation explicitly locates the reference sensing in the terminal base or connector block and specifies isothermal versions of these assemblies.<FP-TC-120 and cFP-TC-120 Operating Instructions by National Instruments>[p. 7, Cold-Junction Compensation: terminal sensors and isothermal terminal assemblies]{ref}
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