Dielectric constant and loss measurements at elevated temperatures

It is pointed out that while the importance of dielectric constant and loss measurements at elevated temperatures is generally acknowledged, a careful survey shows that only a few ASTM methods covering a wide range of electrical insulating materials contain detailed, or even adequate, instructions for carrying out such measurements. Recommendations are made for the early correction of this situation. Some general precautions to be observed to minimize common sources of inaccuracy in elevated temperature dielectric constant and dissipation factor measurements are outlined. These precautions depend strongly upon the nature of the materials being tested, the frequencies at which measurements are performed, the maximum temperatures to be covered, the test enclosures employed, and other factors too frequently overlooked.