Digital inductive position sensor

• US 6,642,711 B2
• Filed: 01/10/2002
• Issued: 11/04/2003
• Est. Priority Date: 01/24/2001
• Status: Expired due to Fees

• 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.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US10/043,406
• Publication Number:
  US 20020097042A1
• Time in Patent Office: 663 Days
• Field of Search: 324/207-6-2, 324/207.24, 324/207.25, 336/45, 336/75, 336/77, 336/79, 336/130, 336/131, 336/192, 336/199, 336/200, 337/06, 337/08, 340/870-2-8, 318/660, 318/661, 341/15
• 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,

a plurality of differential sense coils disposed on a planar surface in magnetic field receiving relationship with the at least one drive coil, each sense coil having at least two loops arranged so that voltage induced in one loop is opposite in polarity to voltage induced in the other loop, and 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 the outputs of the plurality of sense coils for detecting positive and negative pulses in the sense coil providing a digital output, 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, and

a plurality of generally planar targets having an electrically conductive portion movable over the plurality of sense coils within the magnetic field of the drive coil, said plurality of sense coils arranged next to one another along a selected direction and a separate target provided for each loop being movable sequentially perpendicular to the selected direction.

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

3. A non-contact position sensor according to claim 2 in which the di/dt pulse is generated approximately every millisecond.

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

5. 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.

6. A non-contact position sensor according to claim 1 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.

7. A non-contact position sensor according to claim 6 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.

8. A non-contact position sensor according to claim 6 further comprising magnetic field shaping material disposed in vias interconnecting loops of the sense coils.

9. 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.

10. A non-contact position sensor according to claim 6 in which the drive and sense coils are arranged on one layer of the circuit board.