Do you know how does a vibration measure with proximity probe?


Do you know how does a vibration measure with proximity probe?

Proximity sensors detect the presence or absence of objects using electromagnetic fields, lights, and sound. There are many types of proximity sensors each suited to many application and environment.

How does the vibration sensor work?

• The system provides an output voltage that is proportional to the distance between the probe and the target. Also, it can measure static (position) and dynamic (vibration) values.

• The sensor itself is an encapsulated coil of wire, energized with high-frequency alternating current (AC).

• The magnetic field produced by the coil induces an eddy current in the metal shaft of the machine as though the metal piece were a short-circuited a secondary coil of the transformer with the probe’s coil as the primary transformer winding.

• The closer the shaft moves towards the sensor tip. The tighter is the magnetic coupling between the shaft and the sensor coil and stronger the eddy current.


• The high frequency oscillator circuit providing the sensor coil excitation signal becomes loaded by the induced current.

• Therefore, the oscillator’s load becomes the direct measurement of how close the probe tip is to the metal shaft.

• In the Bently Nevada’s design, the oscillator circuit providing the sensor coil excitation is called proximity.

• The proximeter module is powered by an external DC power source and drives the sensor coil through a coaxial cable.

• Proximity to the metal shaft is represented by a DC voltage output from the proximity module with 200 millivolts per mil (I mil = 1/1000 inch) of motion being the standard calibration.

• When the proximity provides a low power radio frequency (RF) signal.

• Also, when no conductive material is within the range of RF signal which surrounds the probe tip, virtually all of the power released to the surrounding area has returned to the probe.

• When the conductive surfaces approach the probe tip, the Rf signal sets up a small eddy current on the surface.

• This eddy current creates a small power loss in the RF signal. When the vibration tip comes nearer to the target the greater the power loss.

• The system uses this power loss to generate an output voltage.

• The output voltage of the proximeter is linearly proportional to the gap over a wide range.