Displacement Measurement Vibration Measurement

What is an eddy current sensor?

An eddy current sensor is a displacement measurement sensor it can be considered as the improved version of an inductive proximity sensor. This sensor is composed of two coils one is the active or sensor coil and the other is the reference or balance coil. The eddy current sensor would measure the distance between the sensor head and an electrically conducting surface, the operation of this device is based on eddy current. The eddy current is created by electromagnetic induction. If we apply an alternating current to the conductor like a copper wire, then a magnetic field is produced around the conductor. This magnetic field would increase if there is an increase in current. So if we bring another conductor in place of this then the second conductor would be affected by the magnetic field and thus it would create an induced current. This sensor is used for vibration measurement because of its non-contact measurement and they would only detect conductive materials that are non-magnetic.

What are the features of eddy current sensors

The eddy current sensors is a non-contact device that can do the high-resolution measurement of the position and also the changes in the position of the conductive object. We can see eddy current sensors in many industrial applications because of their high resolution and their ability to operate in dirty environments. The operation of an eddy current sensor is similar to an inductive proximity sensor both of them work by the principle of electromagnetic induction for their operations. The major difference between the eddy current sensor and the inductive position sensor is that the eddy current sensor uses an air coil along with their advanced electronics. So all this feature makes eddy current sensor better than the inductive proximity sensor.

What are the uses of eddy current sensor?      

The eddy current sensor output represents the size of the distance between the probe and the conductor material, so this device can be calibrated to measure the position or displacement of the target. So this sensor can be used in monitoring or detecting the precise location of an object such as a machine tool. This device can also be used to locate the final position of precise equipment such as a disk drive. This device is also suitable to detect the alternating positions of a vibrating conductor due to its non-contact operation it will be very useful for this purpose.

How does an eddy current sensor work? What are the major parts of the eddy current sensor?

The major parts of the eddy current sensor is a sensor coil, target, the sensor drive electronics, and a signal processing block. The resonance frequency of this sensor is according to the sensor coil. The sensor coil is the active coil and this coil would detect the presence of nearby conductive objects. There is also another coil called balance coil which is used to balance the output bridge circuit for temperature compensation. The operation takes place with the help of a magnetic field, alternating current is produced in the sensing coil by the driver. This would create an alternating magnetic field and also would create a current in the target material and it is eddy current. The eddy current would create an opposing magnetic field and this would resist the field being generated by the probe coil. The magnetic field interaction is dependent upon the distance between the probe and the target object. So when the distance changes the electronics would detect the change in the field interaction and produce a voltage output that is proportional to the change in distance between the probe and the target.

What are the advantages of an eddy current sensor?

  • Low cost
  • Compact
  • High reliability
  • High sensitivity to small displacements
  • It can detect vibration and also can detect the position
  • High resolution
  • It is resistant to oil, dust, and dirt
  • High-frequency response
  • This device is not sensitive to the material in the gap between the probe and the conductor

What are the disadvantages of an eddy current sensor?

  • Limited range
  • Calibration is needed because the conductivity and shape of the object that is to be detected could affect the sensor temperature-dependent.
  • It can only detect conductive materials that have a good thickness, so it cannot detect non-conductive materials and also the conductive materials that have less thickness
  • The relationship between the distance and impedance of the coil is nonlinear and temperature-dependent

What are the applications of eddy current sensors?

  • Machine tool monitoring
  • Dynamic motion
  • Precision stage positioning
  • Machine tool monitoring
  • Identification of metals
  • Structural testing

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