Capacitative displacement- and position measurement instrument for e.g. subsea valves, includes inner and outer sections with dielectric supports moved by adjuster

摘要

A second inner section (6) is located inside the first inner section (2). A second dielectric support (8) moves in the intervening gap (7). First and second dielectric supports (5, 8) are connected to move together with an adjuster (9) or actuator, relative to the first and/or second inner sections. The inner sections are tubular. The sections (2, 3, 6) have surface structures affecting capacity in the direction of movement of the dielectrics. The outer section is the adjustment device (3). It is an outer casing (12). It is the inner side of a cavity. The outer section is conductive. Variants of the structures affecting capacity are described. A read-out device for capacity determines coarse and fine position values. Capacities are of the order of nF per meter length. There is a band pass filter in the read out device. Capacity is controlled in frequency bands of 1kHz to 10 MHz, especially 50 kHz to 1 MHz. The capacitors are divided into segments and wired symmetrically to the read-out unit. Capacitative sections are fed in antiphase to the outer section. The read out and analysis unit adds difference signals produced. Coarse and fine evaluations are carried out simultaneously for difference signal determination.