ASTM D257, IEC 62631-3-1 test method determines Surface Resistivity and Volume Resistivity of insulating materials. Indi rect measurements of moisture content, degree of cure, mechanical continuity, or different types of deterioration are frequently made using the values of resistivity or conductivity. The degree of correlation found by supporting theoretical or experimental investigations determines how helpful these indirect measurements are. The low-frequency dielectric breakdown and dissipation factor characteristics of materials can be predicted by resistivity values. Read more about ASTM D257 below.... Read More
ASTM D257, IEC 62631-3-1 test method determines Surface Resistivity and Volume Resistivity of insulating materials. Indirect measurements of moisture content, degree of cure, mechanical continuity, or different types of deterioration are frequently made using the values of resistivity or conductivity. The degree of correlation found by supporting theoretical or experimental investigations determines how helpful these indirect measurements are. The low-frequency dielectric breakdown and dissipation factor characteristics of materials can be predicted by resistivity values. Read more about ASTM D257 below.
ASTM D257 test method covers direct-current (DC) procedures for measuring DC insulation resistance, volume resistance, and surface resistance. Volume and surface resistivity of electrical insulating materials are calculated from volume and surface resistance values and specimen and electrode dimensions. Corresponding conductances and conductivities are also calculated consequently. Volume resistivity or conductivity determinations are often used to check the uniformity of an insulating material during its production and processing. Resistivity values provide an indirect measure of moisture content, degree of cure, mechanical continuity, or deterioration of materials. ASTM D257 test results also help in detecting conductive impurities that affect the quality of the material and that are not readily detectable by other methods.
Test Procedure:
For the ASTM D257 test, a standard size sample is placed between two electrodes. Then, a potential of specified voltage is applied for 60 seconds and the resistance is measured. Finally, the volume or surface resistivity is determined and the apparent value is given for 60 seconds of electrification time.
All dielectric resistances or conductances are dependent on the amount of applied voltage and the duration of electrification (along with the environmental variables). To make the measured value of resistance or conductance relevant, these must be known and reported.
Conductivity and resistivity alter with temperature and humidity. When planning for operating conditions, these changes must be taken into account.
To assist in designing an insulator for a given application, volume resistivity or conductivity is estimated from resistance and dimensions data. Volume resistivity or conductivity measurements are frequently used to examine the homogeneity of an insulating material, either in terms of manufacturing or to find conductive impurities that degrade the material’s quality but are difficult to find using other techniques.
Video 01: ASTM D257 Tester
Specimen size:
A 4 inch disk is desirable, or a 4 inch square can also be used for the ASTM D527 test. The least possible size of a specimen is a 3.5 inch disk.
Data:
Surface and Volume resistivity is calculated. Volume Resistivity is given in ohms-cm Surface Resistivity is given in ohms (per square)
Conclusion:
ASTM D257 is a standard test method for DC Resistance or Conductance of Insulating Materials. The test results also help in detecting conductive impurities that affect the quality of the material and that are not readily detectable by other methods.
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