Measurement of dc dielectric conductance (reciprocal resistance) at elevated temperature

The general principles given in ASTM D 257(1) apply to measurements of dielectric conductance at elevated temperatures. However, special precautions must be taken in the design of the cell or holder and the measuring circuit to insure that the supporting insulator conductances are Iow enough so that they do not appreciably affect the instrument indication when the conductance of a specimen is being measured. This includes conductance between the measuring electrode and the guard ring when volume conductance is being measured. This generally requires that the supporting insulators for the measuring electrode be Iocated outside the heated area. lt is possible to have the supporting insulators in the heated area if special insulating materials are used and special care is taken to have long lengths of insulators with relatively small cross section. Surface conductance usually has little meaning at elevated temperatures.