Displacement Determination of the Guard Electrode for the New Calculable Capacitor at NIM
We present our continuing work on the displacement determination of the guard electrode for the new vertical calculable capacitor. We describe a method for determining the displacement by actively locking the Fabry-Perot interferometer to a stabilized laser at two cavity lengths of interest. In order to lock the interferometer tightly, the modulation width of the laser is optimized for the full-width at half-maximum at the two different cavity lengths. For each of the cavity lengths, the Fabry-Perot interferometer is maintained at its resonance, and the cavity length is quantized with a space of λ/2. Then, its corresponding ratio between the fixed standard capacitor and the calculable capacitor is accurately measured by a capacitance bridge. The two main parameters for determining the displacement between the two cavity lengths-i.e., the difference in order number (AN) of the interferometer and the laser wavelength (λ)-are obtained from the capacitance bridge measurement based on a 1-pF standard capacitor with a priori value and the accurate wavelength measurement of an iodine laser, respectively. Evaluation of the displacement sensing system confirms a relative uncertainty of 5.2 × 10-9 over a range of 205 mm.
A novel hollow active auxiliary electrode applied for the vertical calculable cross-capacitor at NIM
In order to compensate the end-effect error in the vertical calculable cross-capacitor with one fixed and one movable guard electrodes, two different methods including the nosepiece and the modified active auxiliary electrode are usually adopted in the main worldwide national measurement institutes. However, the latter electrical approach will have some difficulties in assembling the mirrors for the resonant cavity of Fabry-Perot laser interferometer. This paper describes one novel hollow active auxiliary electrode which can satisfy the optical requirements and the model experimental results show that it has similar excellent compensation effect with the modified active auxiliary electrode.
Calculation of Complex Radiant Heat Load From Surrounding Radiator Surface Temperatures
Abstract A method for calculating the radiant heat exchange between an absorber and individual radiating components in its surroundings is reported. Radiator surface temperatures, ambient and absorber temperatures, and configuration factors for radiating components in the surroundings are used in the customary radiant heat exchange formulae. Simplified methods for calculating or estimating configuration factors for radiators of various shapes solely from angles, subtended at the absorber by the radiators are presented. The method has been verified in the laboratory under controlled conditions and has been used to advantage in the field studies. The method has advantages over the globe therometer method in certain applications.