Can you explain me details of eddy current method to measure vibration on rotor? And I really wonder why sensor shows -10V dc when Turbine is in shutdown condition?
These transducers work on the principle that the magnetic field produced around a coil by an alternating currents induces eddy currents in any electrically conducting material near to coil.The transducer function is to generate a voltage which is proportional to the gap between the probe tip and the observed surface.
When a conductive material approaches the probe tip, eddy currents are generated on the surface of the material, resulting in a power loss in the RF signal. As a power loss developed in the RF signal, the output signal at the Oscillator / Demodulator( Proximotor in Bently Nevada) is reduced proportionally. As the observed conductive surface comes closer to the probe tip, more power is absorbed by the eddy currents on the surface of the material.
The Oscillator / Demodulator(Proximitor)measures the magnitude of the RF envelope, and provide a negative dc output signal proportional to the peaks of the envelope.
About the 10 Vdc, in fact it is the gap that you adjust to have for a linear response based on the rotor movement and the response of the probe and proximitor, you should set the probe on the position that the movement does a symmetrical movement.
Thanks for the answer. I got so many things about working principle of sensor. However, I couldn't get why sensor gives "-"(minus) output voltage? Is there any trick point of being minus voltage?
Maybe it would be minus voltage because of conducting surface has larger area than probe tip and that's why it provides bigger voltage than the voltage provided by RF signal??
