Patent ID: 7918801
Filing Date: 2011-04-05
Classification: A61B

Abstract:
1. A sensor system for monitoring the displacement between movable parts of an object comprising: an electrical sensor comprising two components, one component being adapted to be positioned within the other for generally linear movement there between, and having input and output circuits, wherein the electrical impedance of the sensor changes as a function of the relative displacement between the components, the components of the sensor being adapted to be attached to different movable parts of the object for providing impedance changes corresponding to displacements; a circuit for applying pulses to the input circuit wherein the output winding outputs decaying signals, the rate of decay being a function of the relative displacement between the components, and a monitoring circuit is responsive to the output signal decay rate for providing indications of the displacements between the movable parts of the object, wherein the sensor components comprises a coil having an input winding and an output winding and a magnetic core extending into the coil for generally linear relative movement there between, wherein the inductance of the sensor changes as a function of the relative displacement between the core and the coil, the coil and core being adapted to be attached to different movable parts of the object, wherein the monitoring circuit comprises a circuit for measuring the amplitude of the decaying signal after the application of the pulses to the sensor as an indication of the displacements, wherein the monitoring circuit includes a storage circuit for storing the magnitudes of the decaying signals at selected times subsequent to the application of the electrical pulses, wherein the monitoring circuit varies the relative timing between the application of the electrical pulses and the operation of the storage circuit, and wherein the monitoring circuit comprises: a circuit for amplifying the magnitude of the decaying signals and applying the value of the amplified signals at controlled times to the storage circuit; a circuit for sensing when the values of the decaying signals from the amplifying circuit are in saturation or below a reference level, and the control circuit is responsive to the sensing circuit to adjusts the controlled times in a direction so that the amplifier circuit operates between saturation and the reference level.