Electricity: measuring and testing – Conductor identification or location – Inaccessible
Patent
1978-04-13
1980-06-03
Krawczewicz, Stanley T.
Electricity: measuring and testing
Conductor identification or location
Inaccessible
G01R 2702
Patent
active
042064015
ABSTRACT:
An electrical length-measuring system comprises two capacitors and electronic means for obtaining an indication voltage proportional to the displacement. The measuring capacitor, whose capacitance is varied in a linear manner by the displacement to be measured, is connected to a reference a.c. voltage, whilst the reference capacitor with the same dielectric is connected to a measuring a.c. voltage of the same frequency and opposite phase, whose amplitude can be varied by electronic means in such a way that the a.c. voltage induced on an electrode common to both capacitors becomes zero, forcing the measuring a.c. voltage to be proportional to the displacement.
Preferably the capacitance change of the measuring capacitor is brought about by an earthed screen inserted between both electrodes. In the system specifically described and illustrated, the measuring capacitor comprises two coaxial cylindrical electrodes and a coaxial cylindrical screen is inserted axially between the electrodes as a function of the displacement.
In the described and illustrated system also, the a.c. voltages are of a rectangular nature, making it easy to eliminate errors due to transient couplings.
REFERENCES:
patent: 2978638 (1961-04-01), Wing et al.
patent: 3631430 (1971-12-01), West
patent: 3845377 (1974-10-01), Shimotori
patent: 3857092 (1974-12-01), Meyer
patent: 3928796 (1975-12-01), Kaiser
Greigg Edwin E.
Krawczewicz Stanley T.
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