Agilent Technologies 16451B, Operation Manual

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Guard Electrode
The dielectric constant of the disk material shown in Figure 3-3 is
calculated from the measured capacitance value , as above-mentioned.
When the capacitance of the disk material is measured, there is
measurement error caused by stray capacitance at the edge of the test
material, as shown in the left of gure of Figure 3-4. When the guard
electrode as used by the 16451B surrounds the guarded electrode as
used by the 16451B , it is possible to measure the capacitance of the
test material accurately , because the guard electrode can avoid the
stray capacitance at the edge of the electrode as shown in Figure 3-5
Figure 3-4. Capacitance Measurement using Unguarded Electrode System
Figure 3-5. Capacitance Measurement using Guarded Electrode System
3-8 Operation