Non-contact position sensor and method

• US 20020097042A1
• Filed: 01/10/2002
• Published: 07/25/2002
• Est. Priority Date: 01/24/2001
• Status: Active Grant

• Current Assignee: Sensata Technologies Incorporated (Sensata Technologies Holding Plc)
• Original Assignee: Texas Instruments, Inc.
• Inventors: Huang, Lidu, Foelsche, Gerhard A., Fleischfresser, Gerald H., Kawate, Keith W.
• Granted Patent: US 6,642,711 B2
• Time in Patent Office: Days
• US Class Current: 324/207.17
• CPC Class Codes: G01B 7/003 for measuring position, not involving coordinate determination coordinate measuring G01B7/004
• CPC Class Codes: G01D 5/2053 by a movable non-ferromagnetic conductive element
• CPC Class Codes: G01D 5/2225 by a movable non-ferromagnetic conductive element
• CPC Class Codes: G01D 5/2291 Linear or rotary variable differential transformers (LVDTs/RVDTs) having a single primary coil and two secondary coils

Abstract

A differential pulse transformer having a drive coil (10a) and differential sense coils (10b) are disposed on a planar surface with a target (10e, 10f) movable over the sense coils to cause an imbalance in magnetic field when a large di/dt pulse is generated in the drive coil. A detection circuit senses the imbalance and provides a digital output accurately identifying the position of the target. Coil and target embodiments include relatively small secondary coils and relatively long targets (10b, 10e/10f; 12b, 12e/12f and 14b) and relatively large secondary coils and short targets (16b, 16c; 18b, 18c; 20b and 22b).

Claims

1. A non-contact position sensor system comprising

at least one primary drive coil disposed on a generally planar surface, the drive coil having an input,

at least one differential secondary sense coil disposed on a generally planar surface in magnetic field receiving relationship with the drive coil, the sense coil having an output,

a drive circuit connected to the input of the drive coil for providing a large di/dt pulse creating a magnetic field and a detection circuit connected to output of the sense coil for detecting positive and negative pulses in the sense coil providing a digital output, and

a generally planar target having an electrically conductive portion movable over the sense coil within the magnetic field of the drive coil.

2. A non-contact position sensor according to claim 1 in which the sense coil has at least two loops arranged so that voltage reduced in one loop is opposite in polarity to voltage induced in the other loop.

3. A non-contact position sensor according to claim 1 further comprising a plurality of differential sense coils disposed on a planar surface in magnetic field receiving relationship with a drive coil and being connected to the detection circuit.

4. A non-contact position sensor according to claim 1 in which the di/dt pulse is approximately at least 1 amp/microsecond.

5. A non-contact position sensor according to claim 4 in which the di/dt pulse is generated approximately every millisecond.

6. A non-contact position sensor according to claim 1 in which the detection circuit includes a latch for holding a detected digital output.

7. A non-contact position sensor according to claim 1 in which the detection circuit includes a diagnostic network to provide fault indication upon sensing selected fault conditions.

8. A non-contact position sensor according to claim 2 further comprising a plurality of differential sense coils disposed on a planar surface in magnetic field receiving relationship with a drive coil and each sense coil being connected to a separate channel in the detection circuit to provide a plurality of bits to form a binary word indicating positional information.

9. A non-contact position sensor according to claim 8 in which the plurality of sense coils are arranged next to one another along a selected direction and a separate target is provided for each loop and is movable generally perpendicular to the selected direction.

10. A non-contact position sensor according to claim 8 in which the loops of each sense coil are arranged along a selected direction and the plurality of sense coils are arranged next to one another along a direction generally perpendicular to the selected direction and the target extends across the plurality of sense coils and is movable along the selected direction.

11. A non-contact position sensor according to claim 10 in which the sense coils are arranged along a straight line.

12. A non-contact position sensor according to claim 10 in which the sense coils are arranged along an arc of a circle.

13. A non-contact position sensor according to claim 2 further comprising a circuit board having a plurality of layers, the drive and sense coils being disposed on at least one of the layers, the circuit board having vias formed with an electrically conductive lining extending between at least some of the layers and the loops of the sense coils have circuit portions on another layer interconnected through vias to provide opposite current directions.

14. A non-contact position sensor according to claim 13 further comprising at least one ground layer of electrically conductive material formed on a layer of the circuit board for shielding the detection circuit from stray electromagnetic fields.

15. A non-contact position sensor according to claim 13 further comprising magnetic field shaping material disposed in vias interconnecting loops of the sense coils.

16. A non-contact position sensor according to claim 1 in which the loops of each sense coil have a cross-over point at which the loops of each sense coil are interconnected and the loops have a width which is essentially equal at a location adjacent to the cross-over point.

17. A non-contact position sensor according to claim 16 in which at least one portion of a sense coil has an elongated, narrowed section.

18. A non-contact position sensor according to claim 13 in which the drive and sense coils are arranged on one layer of the circuit board.