| 摘要 |
A safety valve, coupled to a pressure chamber, includes a closure element which is translatable substantially along a reference axis. The device includes a spindle nut (60) and an associated extension member adapted for coupling to the spindle (14) of the valve. The extension member includes an annular permanent magnet (76) positioned thereon having its principal axis co-linear with the first reference axis (70). This magnet assembly provides a substantially uniform magnetic field at its periphery which is substantially symmetrical about the reference axis. The device further includes a cylindrical housing member (40) which includes a generally cylindrical inner surface which extends about and is uniformly displaced from the magnet assembly (76) for substantially all positions of the magnet assembly as the spindle moves along the reference axis. The cylindrical housing assembly includes one or more reed switches (50, 52) in close proximity to the inner cylindrical surface aligned with their principal axis parallel to the reference axis. The spacing between the magnet assembly and the reed switches is selected so that as the magnet assembly passes one of the reed switches, that reed switch changes from open to closed, and then back to open again.
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