Specifications

The four-terminal pair (4TP) configuration solves the mutual coupling problem because it uses coaxial
cable to isolate the voltage sensing cables from the signal current path (Figure 3-5). Since the return
current flows through the outer conductor of the coaxial cable, the magnetic flux generated by the
inner conductor is canceled by that of the outer conductor (shield). The measurement range for this
configuration can be improved to below 1 Ω. The impedance measurement range realizable for this
configuration depends on the measurement instrument and on how well the 4TP configuration is
strictly adhered to up to the connection point of the DUT. If the cables are not connected properly,
measurement range will be limited, or in some cases, measurement cannot be made. Figure 3-5 (d)
shows an example of incorrect configuration.
Figure 3-1. Two-terminal (2T) configuration
3-2