Inductive position detection
A position detecting system detects and responds to the movement of a target through a sensing domain area of a plane. The movement causes the amount of the target that lies within a first sensing domain area of a first sensor to change. A second sensor detects a height from the plane to a sensor for enhancing accuracy of measurements from the first sensor.
1. A system, comprising:
a sensing area including a surface orthogonal to a longitudinal axis;
a first sensor having a coil around the longitudinal axis, the coil configured to generate a time-varying magnetic field responsive to an electrical stimulus, the time-varying magnetic field having magnetic field lines intersecting the sensing area, and the coil having an inductance that changes as a conductive target moves within the sensing area relative to the coil;
a second sensor having a first output and configured to:
measure a distance along the longitudinal axis between the coil and the surface; and
provide a first value at the first output indicative of the measured distance;
an inductance-to-digital converter having a stimulus output and a second output, and configured to:
apply the electrical stimulus to the coil via the stimulus output;
measure the inductance by measuring a change in resonance of the coil; and
provide a second value at the second output indicative of the measured inductance; and
circuitry having first and second inputs, the first input coupled to the first output, the second input coupled to the second output, and the circuitry configured to:
responsive to the first value, determine a longitudinal component of a coupling factor between the coil and the target along the longitudinal axis, the coupling factor indicative of a difference between the inductance of the coil and a nominal inductance of the coil;
responsive to the longitudinal component, scale the second value to compensate for a dependency between the inductance and the distance along the longitudinal axis; and
determine a position of the target within the sensing area responsive to the scaled second value.
2. The system of claim 1 , wherein: the target receives an amount of magnetic flux from the time-varying magnetic field; the amount of magnetic flux received by the target changes as the target moves within the sensing area relative to the coil; and the inductance changes responsive to a change in the amount of magnetic flux received by the target.
3. The system of claim 1 , wherein the coil has a quality factor.
4. The system of claim 1 , wherein the target is shaped to variably cover the sensing area according to a movement of the target within the sensing area.
5. The system of claim 4 , wherein the movement of the target within the sensing area includes a translation of the target relative to the sensing area.
6. The system of claim 4 , wherein the movement of the target within the sensing area includes a rotation of the target relative to the sensing area.
7. The system of claim 1 , wherein the circuitry includes a processing circuit.
8. The system of claim 1 , wherein the target is a first target, the sensing area is a first sensing area, and the second sensor is configured to generate a reference inductance responsive to a second target moving within a second sensing area, and the second target is movable in tandem with the first target.
9. The system of claim 1 , wherein the target is a first target, the sensing area is a first sensing area, and the second sensor is configured to generate a reference inductance responsive to a second target moving within a second sensing area, and the second target is movable independently of the first target.