Inductive displacement sensors

• US 4,991,301 A
• Filed: 02/10/1989
• Issued: 02/12/1991
• Est. Priority Date: 02/27/1987
• Status: Expired due to Term

• Current Assignee: Regal Components AB
• Original Assignee: Radiodetection Limited
• Inventors: Hore, Donald L.
• Primary Examiner(s): Will, Thomas B.
• Application Number:
  US07/313,186
• Time in Patent Office: 732 Days
• Field of Search: 33/366, 33/1 N, 33/1 PT, 336/135, 324/207.15, 324/207.18, 324/207.23, 324/207.24, 324/207.25, 340/870.31
• US Class Current: 33/366.25
• CPC Class Codes: G01C 9/06 Electric or photoelectric indication or reading means
• CPC Class Codes: G01D 5/2013 by a movable ferromagnetic element, e.g. a core G01D5/2033 takes precedence

Abstract

Two members 21,22 are relatively displaceable along a linear or circular path. One member 21 provides a plurality of coil portions along the path. Their individual inductances are dependent on the configuration of the second member 22. For example, the first member 21 may be an annular stator with inward radial projections k,l,m . . . on which the coil portions are wound, alternately in different senses so that the flux path tends to loop in and out. The second member 22 may be an annular rotor, one section 23 being ferromagnetic and the other section 24 being non-ferromagnetic and/or having a conductive screening layer. Alternatively the second member may be mercury 42 half-filling an annular conduit 40 which surrounds a static ferromagnetic core 44 (FIG. 9). A particular characteristic is that for any relative position of 21 and 22, half the coil portions of 21 have a different inductance from the other half.

Claims

1. Apparatus for use in monitoring displacement along a displacement path, said apparatus comprising first and second members extending along said displacement path and separated by a constant spacing, said first member comprising a wound portion having a single winding which provides a multiplicity of serially connected coil portions arranged as wound salient poles disposed successively along said displacement path with the axes thereof intersecting said displacement path;

said poles being wound so that alternate poles are of opposite polarity;

said multiplicity of serially connected salient poles including a first terminal at one end of the series of poles, a second terminal at the other end of the series of poles, and a central tapping connection;

said second member comprising an inductance varying means for providing, along with displacement path, regions of different effective permeability to alternating magnetic flux which affect the inductances of adjacent coil portions of said single winding;

at least a portion of said inductance varying means being displaceable relative to said first member along said displacement path to effect displacement of the regions of different effective permeability relative to said coil portions of said single winding such that, for any relative position, the coil portions of one half of the length of the wound portion have higher inductance than the coil portions of the other half;

the apparatus further including means for supplying an alternating electrical voltage across said first and second terminals so that, when alternating current is applied across said terminals and said relative displacement is effected, the voltage at the central tapping connection varies with a substantially linear analog characteristic for a displacement corresponding to one half of the length of the wound portion, and continued displacement in the same sense for a further half length restores the voltage to its original value in a symmetrical manner;

said voltage providing analog electrical output data relating to said displacement.

2. Apparatus according to claim 1 wherein said first member includes a ferromagnetic core with slots so as to define salient ferromagnetic core portions therebetween, said serially connected coil portions being wound on respective ones of said core portions.

3. Apparatus according to claim 2 wherein said slots are skewed relative to said displacement path so as to smooth the variation with displacement of the voltage at the central tapping connection.

4. Apparatus according to claim 1 wherein said regions of different effective permeability of the second member comprise two regions having an interface, and said interface is skewed relative to said displacement path so as to smooth the variation, with displacement, of the voltage at the central tapping connection.

5. Apparatus according to claim 1 further including signal processing means electrically connected to the central tapping for detecting the voltage thereat so as to provide a reading indicative of the displacement.

6. Apparatus according to claim 5 in which said winding has a pair of intermediate tapping connections provided respectively midway between the first terminal and the central tapping, and midway between the central tapping and the second terminal;

said intermediate tapping connections being electrically connected to the signal processing means which is arranged to detect the voltage across said connections, to detect whether this voltage is above or below the midway value, and to thereby determine whether the voltage at the central tapping corresponds to a displacement in the range of the first half length of the wound portion or in the range of the second half length thereof.

7. Apparatus according to claim 1 wherein said first member and at least a portion of said relatively displaceable second member are relatively rotatable, and said predetermined path is circular.

8. Apparatus according to claim 7 wherein a rotatable one of said first member and said at one portion of said relatively displaceable second member is biased by gravity to a predetermined angular orientation relative to the horizontal, so that said electrical output data relate to the inclination of the apparatus.

9. Apparatus according to claim 1 wherein said second member includes a separated ferromagnetic core which is static and is separated from said coil portions by said path;

said second member further including a displaceable portion comprising screening means extending over a length of the path equal to one half of the length of the wound portion.

10. Apparatus according to claim 9 wherein the first member comprises a stator including an annular member with radially extending core portions bearing said coil portions;

said separated ferromagnetic core is located radially within the annular member; and

said screening means comprises an annular conduit located between the separated ferromagnetic core and the coil portions, said conduit being partly filled with a conductive fluid.

11. Apparatus according to claim 9 wherein said path is linear and said displaceable portion of the second member comprises a plurality of screening means spaced from one another by a distance equal to one half of the length of the wound portion, each screening means extending over a length of the path equal to one half of the length of the wound portion.

12. Apparatus according to claim 1 wherein said second member comprises a ferromagnetic core member which is relatively displaceable along said path;

a portion of the ferromagnetic core member of said second member including short circuiting means on the surface thereof to reduce its effective permeability.

13. Apparatus according to claim 1 wherein said second member comprises a relatively displaceable core member comprising, in series along said path, a ferromagnetic portion and a non-ferromagnetic portion.