Variable differential transformer apparatus

• US 4,149,133 A
• Filed: 10/14/1977
• Issued: 04/10/1979
• Est. Priority Date: 10/14/1977
• Status: Expired due to Term

• Current Assignee: Johnson Service Company
• Original Assignee: Johnson Controls, Inc. (Johnson Controls International plc)
• Inventors: Hilgert, Adolph J.
• Primary Examiner(s): Kozma, Thomas J.
• Application Number:
  US05/842,288
• Time in Patent Office: 543 Days
• Field of Search: 336/30, 336/136, 336/130, 336/132, 336/83, 336/134
• US Class Current: 336/30
• CPC Class Codes: G01D 5/2258 by a movable ferromagnetic element, e.g. core
• CPC Class Codes: G01D 5/2291 Linear or rotary variable differential transformers (LVDTs/RVDTs) having a single primary coil and two secondary coils
• CPC Class Codes: G01L 9/0085 using variations in inductance
• CPC Class Codes: H01F 21/06 by movement of core or part of core relative to the windings as a whole

Abstract

A linear variable differential transformer includes a primary winding and two secondary windings in spaced stacked relation on a core unit. The core unit includes similar cup-shaped pot cores mounted in opposed opening relationship and having abutting cylindrical outer walls and spaced cylindrical inner walls define an annular chamber within which the windings are located. A core axis located within the central air gap between the inner walls and terminates in close relation to the windings. A movable stem couples the core to a pressure diaphragm transducer to locate the core in accordance with pressure.

Claims

1. A position-sensitive linear variable differential transformer apparatus having a primary coil and first and second secondary coils located in stacked relation to the opposite sides of said primary coil and connected in series opposition, comprising a winding core of a low reluctance material and having an inner chamber having a cross-section substantially complementing said stacked coils and having an inner wall, said stacked coils being located in said chamber adjacent the inner wall, said inner wall including a pair of opposed inner core leg portions spaced from each other and axially aligned to define an air gap aligned with the primary winding, said primary winding spanning said air gap, a movable core located in alignment with the opposed inner core leg portions and within said air gap and having a movable support means for selective axial positioning of said core axially within said air gap between the leg portions and thereby the opposite ends of the air gap, said coils and core defining a flux pattern including a pair of flux loops which encompass the primary coil and said secondary coils.

2. The transformer apparatus of claim 1 having a positioning diaphragm chamber unit including a mounting wall and a movable wall, a pressure signal fitting secured to the mounting wall, and a stem member adjustably secured to the movable wall and to the movable core.

3. The transformer apparatus of claim 2 including an outer housing including having an end wall secured to the mounting wall and a tubular side wall extending upwardly in spaced relation to the chamber unit and having an upper reduced end adhesively bonded to only the lower end of the core unit.

4. The transformer apparatus of claim 1 wherein said winding core is a sintered powdered ferrite material.

5. The transformer apparatus of claim 4 wherein said movable core is a high nickel alloy material.

6. The transformer apparatus of claim 4 wherein said windings are wound as annular coils of similar inner and outer diameters and end faces, said coils being located in abutting end-to-end coaxial alignment.

7. The transformer apparatus of claim 6 wherein said movable core is a disc-like member having a non-magnetic stem extending coaxially through a central core opening, said stem being firmly affixed to said core at said opening.

8. The transformer apparatus of claim 1 wherein said secondary coils are wound with a different number of turns, and a position sensitive device coupled to said movable support means, said core has a minimum output position within said air gap adjacent the secondary coil with the lesser number of turns.

9. The linear variable differential transformer apparatus of claim 1 wherein said winding core is formed from corresponding cup-shaped core members, each of said core members having a substantially C-shape with a base connected to an outer leg and and said inner core leg portions being formed by an inner leg substantially shorter than said outer leg, said core members being located in opposed relation and telescoped over said stacked coil assembly with the outer and inner legs aligned.

10. A linear variable differential transformer apparatus having an annular primary coil and first and second annular secondary coils located in stacked relation to the opposite sides of said primary coil and connected in series opposition, comprising a winding core unit including an upper and a lower cup-shaped core, each of said cores having a substantially C-shape with a base connected to an outer leg and an inner leg substantially shorter than said outer leg, said cores being located in opposed relation and telescoped over said stacked coil assembly with the outer and inner legs aligned, said inner legs being spaced to define an air gap therebetween, said primary coil being located spanning the air gap, a movable cylindrical core located between and in alignment with the inner legs and thereby within said air gap and having a movable support means for selective axial positioning within said air gap between a centered position aligned with the primary coil and an off-centered position, said primary coil being operable to create first and second loops in the centered position, said first loop passing through the movable and winding cores and enclosing both the primary and first and secondary coils and said second loop enclosing only the primary coil, said primary coil being operable in an off-centered position to develop third and fourth loops, each of said third and fourth loops enclosing the primary winding and an opposite one of the first and second secondary coils.

11. The transformer apparatus of claim 10 wherein each of said cores is a sintered powdered ferrite material.

12. The transformer apparatus of claim 10 wherein said winding core is a sintered powdered ferrite material and said movable core is a high nickel alloy material.

13. The transformer apparatus of claim 10 wherein said windings are wound as annular coils of similar inner and outer diameters and having flat end faces, said coils being located in abutting end-to-end coaxial alignment, said chamber defined by said cores essentially corresponding to the cross-section of the stacked coils.

14. The transformer apparatus of claim 13 including a winding bobbin with said coils located therein, said bobbin having a tubular base abutting the inner legs and separating plates extended between the coils.

15. The transformer apparatus of claim 14 wherein said movable cylindrical core being an annular core having a central core opening and includes a non-magnetic stem extending coaxially through the central core opening.

16. The transformer apparatus of claim 13 wherein said secondary coils are wound with a different number of turns, and having a position sensitive device coupled to said movable support means, said core has a minimum output position within said air gap adjacent the secondary coil with the lesser number of turns.

17. The transformer apparatus of claim 10 wherein said winding core is a sintered powdered ferrite material, said movable core is selected from the group consisting of a high nickel alloy material and a sintered powdered ferrite material, an annular coil bobbin having three adjacent coil chambers of essentially the same inner and outer diameters and having flat end faces, said coils being located within said chambers in coaxial alignment, said chamber defined by said cores essentially corresponding to the cross-section of the bobbin, and means firmly affixing the bobbin to the core unit.

18. The transformer apparatus of claim 17 wherein said movable cylindrical core is an annular core and includes a non-magnetic stem extending coaxially through a central opening in the annular core.

19. A transformer apparatus of claim 17 having a positioning means for the moving and holding said movable core within said air gap.

20. The transformer apparatus of claim 19 wherein said positioning means includes a closed diaphragm chamber unit having a mounting wall and a movable wall, a pressure signal fitting secured to the mounting wall, and a stem member adjustably secured to the movable wall to the movable core.

21. The transformer apparatus of claim 20 including an outer housing including having an end wall and a tubular side wall, said end wall having an opening, said fitting passing through said opening, means fixedly mounting said mounting wall to said end wall, said core unit having an outer diameter less than said diaphragm chamber unit, said side wall extending upwardly in spaced relation to the chamber unit and having an upper reduced end adhesively secured to only the lower end of the core unit.