Importance

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Abstract

A displacement measurement apparatus includes a primary electrode, and first and second secondary electrodes which are closely spaced apart and together fully span the primary electrode, the primary and secondary electrodes being movable relative to one another without increasing their transverse separation. A charge pumping means is arranged to supply electric charge to the primary electrode through the first secondary electrode during selected first clock periods, and to withdraw charge from the primary electrode through the second secondary electrode during selected second clock periods. The changeover from one mode of operation to the other is made automatically when the sign of the charge on the primary electrode reverses, so that the charge on the primary electrode is successively increased, and then reduced to a low value. The numbers N1 and N2 of charge packets supplied to and withdrawn from the primary electrode during a measurement cycle are counted, and a displacement signal is produced in accordance with the relationship (N1-N2)/N1. The electrical system may also be used for determining in a similar manner the ratio of the capacitances of any two capacitors.

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First Claim