Capacitively coupled ohmic resistance position sensor

An apparatus for measuring position of a target member comprising in combination:

• a) an elongated cylindrical member including at least one of the following two surfaces;
• an external cylindrical surface of a constant cross sectional geometry wherein the elongated cylindrical member may have only the external cylindrical surface, and an internal cylindrical surface of a constant cross sectional geometry wherein the elongated cylindrical member has a hollow construction;
• b) a first electrically conducting elongated member having a finite value of ohmic resistance per unit length thereof and a sizable surface area disposed parallel to the central axis of the elongated cylindrical member in a relationship wherein the sizable surface area of the first electrically conducting elongated member is disposed adjacent to one of the external and internal cylindrical surfaces of the elongated cylindrical member;
• c) a second electrically conducting elongated member having a finite value of ohmic resistance per unit length thereof and a sizable surface area disposed parallel to the central axis of the elongated cylindrical member and parallel to the first electrically conducting elongated member in a relationship wherein the sizable surface area of the second electrically conducting elongated member is disposed adjacent to said one of the external and internal cylindrical surfaces of the elongated cylindrical member;
• d) a capacitively coupling member having a sizable surface area disposed in a sliding relationship following the central axis of the elongated cylindrical member in a relationship wherein the sizable surface area of the capacitively coupling member maintains a close surface-to-surface proximity relationship with a portion of the sizable surface area of the first electrically conducting elongated member and with a portion of the sizable surface area of the second electrically conducting elongated member in an electrically nonconducting relationship at all instants during sliding movement of the capacitively coupling member relative to the first and second electrically conducting elongated members;
• e) means for supplying an input alternating electrical signal to the first electrically conducting elongated member;
• f) means for taking off two output alternating electrical signals respectively from two opposite extremities of the second electrically conducting elongated member;
• and
• g) means for obtaining an electrical variable related to a phase angle difference between the two output alternating electrical signals as a measure of position of the capacitively coupling member relative to at least one of two extremities of the elongated cylindrical member.