Standard Capacitor Calibration Procedure Implemented Using Control Software

Abstract

Abstract NOTE: The first page of text has been automatically extracted and included below in lieu of an abstract ASEE 2004 Standard Capacitor Calibration Procedure Implemented Using Control Software Svetlana Avramov-Zamurovic1, Brian Waltrip2, Andrew Koffman2 and George Piper1 1 United States Naval Academy, Annapolis, Maryland, USA avramov@usna.edu 2 National Institute of Standards and Technology*, Gaithersburg, Maryland, USA Introduction A capacitance scaling method is used to calibrate standard capacitors. This is a very powerful technique that was introduced by Aoki and Yokoi in 1997 [1]. Reference [1] describes the general method and provides a detailed uncertainty analysis. Aoki and Yokoi developed a calibration procedure based on [1] but this reference is insufficient for duplication of the measurement system and implementation of the calibration procedure. The capacitance scaling procedure involves reference point measurements and a series of "scaling" measurements. A commercial capacitance bridge is used in order to obtain reference measurements at 1 kHz. An inductive voltage divider (IVD) with the ratio of 10:1 is used to scale a known capacitance for comparison with a capacitance under test. The measurements are performed over a range of frequencies. This paper will present the capacitance scaling procedure in detail and demonstrate the developed software program that controls the calibration procedure. The challenge of this presentation is to explain a rather sophisticated precision measurement technique in such a way that it may be taught to an interested group of undergraduate students. The software development provides an opportunity to teach the calibration process: from taking measurements to producing a calibration report. Capacitance Scaling Method Modern instrumentation is designed for automated control in order to create custom calibration procedures. In the case when very precise and specialized tests are necessary within the metrology community, it is particularly challenging to establish computer control of an entire procedure. Accurate calibration of capacitors that range from 1nF to 100 µF over a wide frequency range (100 Hz to 100 kHz) is a demanding task. There are several instruments commercially available to measure the impedance of a capacitor. LCR meters are general impedance-measuring instruments that have limited * Electronics and Electrical Engineering Laboratory, Technology Administration, U.S. Department of Commerce. Contribution of the U.S. Government. Not subject to copyright in the U.S.