ASTM D1169 for specific resistance (resistivity) of insulating liquids
ASTM D1169 standard test method for specific resistance (resistivity) of electrical insulating liquids
4. Significance and Use
4.1 The resistivity of a liquid is a measure of its electrical insulating properties under conditions comparable to those of the test. High resistivity reflects low content of free ions and ion-forming particles, and normally indicates a low concentration of conductive contaminants.
5. General Considerations
5.1 Theory and measuring equipment pertaining to this method shall be in accordance with Test Methods D257.
5.2 Where both ac loss characteristic (dissipation factor or power factor) and resistivity measurements are to be made consecutively on the same specimen, make the ac measurement before applying the dc potential to the specimen, and short circuit the cell electrodes for 1 min immediately prior to making the resistivity measurements.
5.3 Make referee tests for resistivity in an atmosphere of less than 50 % relative humidity. For repeatable results make these tests under carefully controlled atmospheric conditions.
5.4 Aside from the adverse influence of contamination on results of the resistivity test, there are other factors that can contribute to variations in the test results as follows:
5.4.1 The use of an instrument not having an adequate range for accurately measuring the current flowing in the circuit. (See Section 6 for two types of recommended instruments.)
5.4.2 When the time of electrification is not exactly the same for every test. Upon the application of voltage, the current flow through the specimen decreases asymptotically toward a limiting value. Variation in the time of electrification can result in appreciable variation in the test results.
5.4.3 Undue length of time required for the test specimen in the cell to attain the desired test temperature. This is one of the main sources of erroneous results. For optimum results, attain the test temperature within 20 min.
5.4.4 Fluctuations in the test voltage (see 6.1.4).
