Eddy current sensor working principle

Isolation sensor work principle When the sensor system is turned on, a high frequency signal is generated in the front of the probe, which is sent to the head of the probe, and an alternating magnetic field H1 is generated around the head. If there is no metal conductor in the range of the magnetic field H1, the energy emitted to this range is released; in turn, if the metal conductor is close to the head of the probe, the alternating magnetic field H1 will generate an eddy flow field on the surface of the conductor. The eddy flow field also produces an alternating magnetic field H2 opposite to H1. Due to the reaction of the H2, the magnitude and phase of the high-frequency current of the probe head coil will change, that is, the effective impedance of the coil is changed. This change is related to the eddy current effect, and is also related to the sideline (with the electrical conductivity, magnetic permeability, geometric shape, coil geometric parameters, the excitation current frequency, and the distance parameters of the metal conductor). It is assumed that the metal conductor is homogeneous, and its properties are linear and isotropic, then the magnetore-metal conductor system of the coil-metal conductor system is the magnetic permeability u, the conductivity σ, the size factor R, the coil and the metal conductor distance δ coil excitation current I and Description of the parameters such as frequency Ω. Therefore, the impedance of the coil can be represented by function Z = f (u, σ, r, Δ, i, ω). If the control U, σ, R, I, ω constant constant, then the impedance z is a single value function of the distance, by the Maxwell formula, the function can be obtained as a non-line function, the curve is "S" type curve. It can be approximately a linear function within a certain range. The change in the coil impedance z is changed by the treatment of the frontier electron line, that is, the change in the distance δ of the head portion coil and the metal conductor is converted into a voltage or current. The size of the output signal varies with the spacing between the probe to the surface of the measured surface, and the eddy current sensor is measured by the displacement, vibration of the metal object, according to this principle. In general, the impedance, inductance, and quality factor of the sensor coil are related to the geometry, conductivity and magnetic permeability of the conductor. Also related to the geometric parameters of the coil, the frequency of the current, and the coil to the pitch of the tested conductor. If a parameter change in the above parameters is controlled, the remaining unchanged, then various sensors can be constituted by the measurement, measurement temperature, hardness, and the like. Read more

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