Portable capacitance standards.
P. Patel, S.A. Awan · 2001
This paper describes capacitance standards made from NPO ceramic dielectric in the range from 100 pF to 1 µF. The standards are encased ina two stage oven to achoeve high temperature stability resulting ina low overall temperature coefficient which is less than 0.05 ppm/K (with typical stability of 0.01 ppm/h). The NPO ceramic is batch selected and trimmed to give close tolerance (better than 100ppm) to the nominal value of the standard. The standards are designed to have good transport behaviour and have found many uses in AC bridge work. The design and manufacture of the capacitors will be discussed and results presented on their temperature coefficient, long-term drift, frequency dependence and dissipation factor.