Eddy current proximity sensors

If you are serving in industry and especially in the maintenance of rotating machinery, surely knows that to measure the vibrations of a machine, it is necessary to support the accelerometer in the bearing housing and simply make the measurement.

Very different it is to measure the geometric position of the shaft from its real center or its vibrations, because it is impossible to support an accelerometer , as the shaft rotates. The best alternative for this measurement is the use of Eddy sensors, or eddy current, as they measured static and dynamic shaft displacement.

Such sensors have the ability to make a position or movement measurement at distance, without contact with the measured piece.
We will not go into the details of how this measurement is achieved, as we should delve into electrical / magnetic theory, and it is not our intention at this time.

Simply installing 1, 2 or up to 3 sensors on an axis (one vertical, one horizontal, and the third axial to the shaft), at distances ranging between 1 and 10 mms, we can make complex measurements of high precision, and see if the axis moves from its geometric center, indicating future failures.

These transducers, are normally applied at low frequencies (below 1000 Hz) usually for turbomachinery friction bearings. The proxímeter, as are they also known, are installed on covers of bearings or at their side and detect the displacement of the shaft relative to its anchor position or geometric axis.

An Eddy type proximity catchment system  consists of a sensor and a signal conditioner. Its frequency response is excellent. They have no lower working frequency limit  since it reaches 0 Hz, and are used in measuring both vibration and  axial axes position.

Univibro has a complete line of EDDY proximity sensors of German technology, with a wide range of special models for various industry applications, covering all needs.

 

Typical installation mode for eccentricity axes measurement.

 

External mounting method.

Main applications of eddy current inspection:

 

VARIABLE	APPLICATION
Electric conductivity.	Classification of alloys. Control heat treatment (grain size, hardness, residual stress). Coating thickness. Thickness of cadmium-plated, electroless nickel.
Magnetic permeability.	Separation of alloys (magnetic materials) Depths of surface treatments. Heat treatment condition. (Magnetic Materials).
Geometry (dimensions).	Thicknesses (thin material)
Homogeneity	Axes eccentricity measurement Cracks Segregations. Seams. Inclusions. Stings. Corrosion. Structural.
Magnetic coupling	Insulation thickness. Thickness of nonmetallic coatings. Diameter.

API 670 Standard
The American Petroleum Institute (API) has published 670 Standard to assist in the standardization of monitoring systems for contactless measurement of vibration, axial position and temperature. The standard is based on the knowledge and experience accumulated of oil refineries and manufacturers of monitoring systems.

The API 670 Standard is a useful reference tool for all users and machine manufacturers, it is highly recommended as a guide for defining, purchasing and installing machinery monitoring systems.

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