A 0.1 to 10 MHz Dielectric Specimen Bridge with Dissipation Factor Accuracy of ±10-6

The Dielectric Specimen Bridge has been developed to measure polyethylene's dissipation factor of approximately 60× 10-6 to an accuracy of approximately 10-6 over the frequency range of 0.1 MHz to 10 MHz. The specimen holder is of the liquid displacement type employing silicone fluid. A specimen consists of two 0.050-inch thick sheets, 2.7 inches wide by 2.0 inches high. Low-impedance coaxial spring fingers provide a highly reproducible connection between the holder and the bridge. The bridge is of the unity ratio type with 100-picofarad ratio arms and adjustable capacitance and conductance standards. The conductance standard contains four decades, each consisting of a small fixed capacitor in series with a resistance decade. A specially developed phase-sensitive detector prevents capacitance changes of several parts per million from obscuring the observation of the desired conductance balance. This detector has continuous tuning and uses heterodyne techniques. The bridge is calibrated with an external conductance standard which consists of a capacitor in series with an interchangeable resistor, and has a geometry and element values such that the radio frequency conductance can be determined from low-frequency measurements. Since the liquid displacement method measures the difference between the dissipation factors of the polyethylene and the silicone fluid, the bridge is being used to make measurements of the dissipation factor of the fluid itself. In addition, measurements are being made of the dissipation factor of air.