Position indicating apparatus

Claim 1

Apparatus for indicating the position of a movable member, said movable member being separated from at least part of the indicating apparatus by a partition of nonmagnetic material, said indicating apparatus comprising: a permanent magnet, said magnet being affixed to and moving with said movable member; a plurality of normally open magnetic flux responsive electrical switches, said flux responsive switches being located on the opposite sides of said partition from said movable member, said flux responsive switches being positioned along a line parallel to the path of motion of said movable member whereby said flux responsive devices will be serially and individually closed during during travel of said magnet with said movable member; means for generating a first plurality of voltages of different magnitude; means for applying said first plurality of output voltages to the first terminals of individual of said flux responsive switches; means interconnecting the second terminals of said flux responsive switches, the magnitude of the voltage appearing on said interconnecting means being indicative of the energization of a particular one of said flux responsive switches; a source of reference potential, the magnitude of the output signal from said reference potential source being adjustable; means connected to said adjustable reference potential source and said interconnecting means for comparing the signal from said reference potential source with the signal indicative of which of said flux responsive switches is energized; means responsive to the sensing of an unbalance by said comparing means for automatically adjusting the output of said reference potential source in stepwise fashion to null said unbalance; and means for providing an indication commensurate with the adjusted output of said reference potential source.