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7
Preparation of test material and test cell
7.1
Solid materials
The following sections base on the international standards for analysis of the dielectric properties of solid
electrical insulation like ASTM D150-18 (ASTM D150-11), D-257-14, IEC 62631-2-1-2018-02 (IEC
60250) or IEC 62631-3-1.
7.1.1
Preparation of solid material test cells
The measured dielectric properties can be influenced by the presence of conductive contaminations or
moisture on the test cell or the material sample surface. Thus, the test cell and its electrodes or contact
surfaces must be cleaned before measurement.
NOTICE
► Follow the cleaning, warning and safety instructions of the test cell
manual.
► The used solvents or cleaning agents must previously been checked to
ensure that they do not contain contaminations which can influence the
measurements. Ensure that the used solvent or cleaning agent leads to
correct results of known low permittivity and dielectric losses. Some
cleaning procedure examples can be found in the international standards
like described above.
DANGER
Death or severe injury caused by fire, poisoning or chemical burn
Ensure the safety conditions for using solvents. Protect persons and
equipment against fire and toxic effects. Read the safety instructions of the
solvent or cleaning agent before cleaning.
7.1.2
Preparation of solid test material
The measurement error of the permittivity is not only caused by capacitance measurement error (see 8.1
"Error correction"), but also by the error in the solid test material dimensions and structure. Therefore, cut
or model the test material accurately and measure the test material sample so that its dimensional error
will not affect the permittivity value.
Size and thickness
In general, the size of the solid material should be large enough to allow its
measurement with the required accuracy. Typically, a capacitance of at
least 100 pF should be formed by the sample (size and thickness) and test
cell. If the capacity is lower, the accuracy is limited and noise influences
can prevent a good measurement result, especially if the dielectric has low
losses. Therefore, usually a low sample thickness is used.
Preparation of test material and test cell
17
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