The characteristics and errors of capacitors used for measurement purposes

This paper deals with the variations of capacitance and loss angle occurring in precision capacitors used for measurement purposes. The degree of accuracy required in current practice is discussed, and compared with the performance of available instruments. The causes of variation are discussed with relation to time, humidity, temperature, frequency, voltage and screening. The properties of materials used in capacitor construction are discussed in relation to the foregoing variables. Special attention is given to the less well-known causes of change in capacitance and loss angle, and also to experimental difficulties which lead to errors in the measurement of these quantities. In particular, attention is directed in an Appendix to an apparently unrealized source of error in loss-angle measurements on samples with a guard ring.