| 摘要 |
Alternating current capacitance measuring bridge for measuring the capacitance of capacitors having one electrode connected to an external earth. It comprises a first metal screen box connected to the common terminal of the secondary windings of a differential transformer and directly to screened coaxial connections of capacitors inside of which an alternating voltage source and the transformer are placed, and means for d.c. supplying the source via internal d.c. supply terminals comprising a first winding connecting to the common terminal of secondary windings and the external earth, a second and third windings connecting to the internal d.c. supply terminals and external d.c. supply terminals, the first, second and third windings having a high impedance at the operational frequency of the source, two capacitors of high impedance inserted between the internal d.c. supply terminals and said first screen box, and two other capacitors of high impedance inserted between the external d.c. supply terminals and the external earth. In addition, the measuring bridge comprises a second metal box screen containing all the elements of the measuring bridge and connected to the external earth. The screened coaxial connections comprise either external conductors connected to the external earth, or internal conductors connected to the first metal screen box and external conductors connected to the external earth, so as to eliminate mutual capacitance errors coming from induced currents between conductors of the screened coaxial connections.
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