Principle Of Four-Terminal Pair Measurement - Keysight E4981A User Manual

Technical Information
Basic Principles of Capacitance Measurement

Principle of four-terminal pair measurement

Generally, in connection methods using common terminal structures, mutual
inductance, interference between measurement signals, and unnecessary
residual elements (especially at higher frequencies) significantly affect
measurements.
The E4981A adopts a four-terminal pair structure to reduce the limitations on
measurements due to these factors and to facilitate stable and accurate
measurements.
Figure E-7
UNKNOWN terminals are four coaxial connector terminals.
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Figure E-7 Principle of four-terminal pair measurement
The four-terminal pair measurement method has advantages in both low- and
high-impedance measurements. The outer shield conductors serve as the
return path of the measurement signal current (not grounded). Current of the
same amplitude flows through the core conductor and the surrounding shield
conductor in opposite directions, and therefore no external magnetic field
occurs around either conductor. In other words, the magnetic field caused by
the inner conductor and that caused by the outer conductor cancel each other
completely. The measurement signal current does not cause any induction
field and, therefore, the test leads do not increase the error due to their
self-inductance or the mutual inductance between different leads.
248
illustrates the principle of four-terminal pair measurement. The
H : Current high terminal
CUR
H : Voltage high terminal
POT
L : Voltage low terminal
POT
L : Current low terminal
CUR
Keysight E4981A 120 Hz/1 kHz/1 MHz Capacitance Meter