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Eddy Current Position Sensors Gabe Poehls Inductance Eddy currents are loops of electrical current induced within conductors as a result of a changing magnetic field. These currents circulate such that a new magnetic field is created to oppose the field that created them. This relationship is shown in the following diagram: Image References: Image #1: https://en.wikipedia.org/wiki/Emil_Lenz Image #2: https://en.wikipedia.org/wiki/Michael_Faraday Image #3: https://www.bluelineengineering.com/ Eddy current position sensors rely on the principle of inductance to determine the proximity of a sensor coil to a conductive target. Inductance is a result of the interaction between magnetic fields and electrical current within a coil of wire. Faraday’s Law and Lenz’s Law describe this interaction: -An electromotive force (EMF) is generated within in a closed loop equal to the rate of change in magnetic flux through the loop. Michael Faraday Emil Lenz -This EMF causes a current to flow through the loop and a magnetic field is formed which opposes the field that caused it. Deriving Self Inductance Self Inductance: Eddy Currents A changing magnetic field is generated in the sensor coil when supplied by an AC Voltage source. As the target approaches the sensor coil, eddy currents are formed within the body of the aluminum target which create a magnetic field of their own to oppose that of the coil. This decreases the net magnetic flux through the coil and with it the measured inductance of the circuit. By measuring inductance at various coil-target distances, a relationship between inductance and target position can be determined. Summer Research Blue Line Engineering specializes in the design and fabrication of high precision eddy current position sensors for various aerospace applications, typically used on fast steering mirrors for laser communication. This summer we worked on developing a modeling process for their line of sensor coils to aid in new position sensor development. ANSYS Maxwell Software used to model coil sensors and perform E&M analysis with an aluminum target (not shown) and collect inductance data Inductance vs. Position for physical test data (red) and ANSYS model data (blue). As the target approaches the sensor (the zero of the x- axis) the inductance of the sensor coil circuit is shown to decrease
