New Fused-Silica-Dielectric 10-and 100-pF Capacitors and a System for Their Measurement

New instruments have been designed to bring to standards laboratories the improved accuracy of capacitor calibrations developed by the National Bureau of Standards. The new 10-and 100-pF reference standard capacitors, based upon an NBS design, use a fused-silica dielectric with gold electrodes to provide the time and voltage stability required for calibrations to parts in 107. To maintain the capacitor temperature constant to within 0.01 °C, one model of the capacitors is designed for use in an oil bath, the other model is fitted with a new, stable, thermostatically controlled air bath. The system to measure these capacitors with a precision of parts in 108 consists of a bridge, detector, and oscillator. For these special measurements and for the general calibration of a wide range of capacitors, the new transformer-ratio-arm bridge has 12 capacitance decades and a range of 10 MAF-10-7 pF, and five conductance decades and a range of 103110-10 tmho. The new phasesensitive detector and power oscillator provide high sensitivity to bridge imbalance over the frequency range 10 Hz-100 kHz.