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Circuits for Measurement of Grounded and Direct Capacitance

IP.com Disclosure Number: IPCOM000094805D
Original Publication Date: 1965-Jun-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Rymaszewski, EJ: AUTHOR [+2]

Abstract

It is not always possible to ground one node of a direct capacitance to convert it into a grounded capacitance nor is it always possible to measure a grounded capacitance as a direct capacitance. Grounded capacitance is defined as capacitance from a nongrounded node to ground. Direct capacitance is defined as a capacitance between two nongrounded nodes excluding the capacitance to other nodes including ground. Circuitry that can be employed to measure both grounded and direct capacitance is shown.

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Circuits for Measurement of Grounded and Direct Capacitance

It is not always possible to ground one node of a direct capacitance to convert it into a grounded capacitance nor is it always possible to measure a grounded capacitance as a direct capacitance. Grounded capacitance is defined as capacitance from a nongrounded node to ground. Direct capacitance is defined as a capacitance between two nongrounded nodes excluding the capacitance to other nodes including ground. Circuitry that can be employed to measure both grounded and direct capacitance is shown.

In circuit A, the exterior region of the transmission line is arranged to provide a reasonable high impedance to one side of the capacitance. This is effected by winding the transmission line around a ferrite cylinder or inserting it through a bore of a ferrite cylinder. This circuit uses the isolation provided by the outer conductor of the transmission line between its outer and inner regions. The circuit also utilizes the ability of the transmission line to transform the impedance of the detector to provide a very low impedance, virtually a short circuit, to the capacitance. In circuit B, the capacitance is coupled to the emitter of a grounded base transistor having a very low input impedance.

Very low source impedance permits the presence of relatively low impedance from one node of the direct capacitance to ground. When the crossover switch is changed to the dashed position, grounded capacitance may be meas...