The working principle of the eddy current sensor, the eddy current effect

When connected sensor system power supply, in the front-end will produce a high frequency signal, the signal through the cable to the probe head, H1 to produce alternating magnetic field around the head. If no metal conductor in magnetic field H1 close, is launched into this energy will be released within the scope of; On the other hand, if there is a metal conductor is close to the probe head, the alternating magnetic field H1 will generate eddy current field in the surface of the conductor, the eddy current field can have a direction contrary to the H1 H2 alternating magnetic field. Due to the adverse effect of H2, can change the probe head coil of high frequency current amplitude and phase, which changes the effective impedance coil. This change is associated with the eddy current effect, are also associated with static magnetism effect (with metal conductor of electric conductivity, magnetic permeability, geometric shapes, coil geometry parameters, the frequency of the exciting current and coil parameters related to the distance to the metal conductor). Assume that the metal conductor is homogeneous, and its performance is linear and isotropic, the permeability of the coil, metal conductor system is u, conductivity sigma, size factor r, coil and metal conductor from the delta coil excitation current and frequency to describe the parameters, such as omega I. Therefore the impedance of the coil available function Z = F (u, sigma, r, delta, I, omega). If the control u, sigma, r, I, omega is constant, then the impedance Z as a single value function of the distance, by maxwell formulas, this function can be obtained as a nonlinear function, for the "S" type curve, the curve within a certain range can be approximately as a linear function. Through the processing of the front-end electronic circuit, the coil impedance Z change, namely the head body coil and the change of the metal conductor from the delta into the change of the voltage or current. The size of the output signal with the probe to the measured body surface spacing between, the eddy current sensor is realized according to the principle of the metal object parameters such as displacement, vibration measurement.