The eddy current sensor consists of a sensor excitation coil and a metal body to be measured. According to Faraday's law of electromagnetic induction, when a sinusoidal alternating current passes through the sensor excitation coil, a positive alternating magnetic field will be generated around the coil, and the metal conductor located in the magnetic field of the cover will generate an induced current, which will generate a new alternating magnetic field. The new alternating magnetic field hinders the change of the original magnetic field and changes the equivalent impedance of the sensor coil.
the change of coil impedance depends entirely on the eddy current effect of the measured metal, which is related to the above factors respectively. If only one parameter in the formula is changed and the other parameters remain unchanged, the impedance z of the sensor coil is only related to this parameter. If the change of the impedance of the sensor coil is measured, this parameter can be determined. In practical application, it is usually to change the distance x between the coil and the conductor, while keeping other parameters unchanged, to achieve displacement and distance measurement.
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1. Generally, the maximum allowable temperature of eddy current sensor is ≤18 degrees. In fact, if the working temperature is too high, not only the sensitivity of the sensor will be significantly reduced, but also the sensor will be damaged. Therefore, when measuring the vibration of high, middle and low shafts of steam turbines, the sensor must be installed in the bearing bush.
2. In order to prevent the magnetic field generated by eddy current from affecting the normal output of the instrument, a certain range of non-conductive medium space must be left around the sensor head during installation. If two or more sensors need to be installed in a certain part at the same time during the test, a certain distance should be kept between the two sensors to avoid cross interference.
3. In addition, the surface area of the measured body should be more than 3 times the diameter of the probe, and there should be no scars, holes and gaps on the surface, and surface electroplating is not allowed. The measured material should be consistent with the material calibrated by the probe and the preamplifier.
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