The Proximity Probe
The Proximity Probe, also called an "Eddy Current Probe" or "Displacement Transducer", is a permanently mounted unit, and requires a signal-conditioning amplifier to generate an output voltage proportional to the distance between the transducer end and the shaft. It operates on a magnetic principle, and is thus sensitive to magnetic anomalies in the shaft -- care should be taken that the shaft is not magnetized to assure the output signal is not contaminated. It is important to realize that the transducer measures relative displacement between the bearing and the journal, and does not measure total vibration level of the shaft or the housing. The displacement transducer is very commonly installed in large machines with journal bearings where it is used to detect bearing failure and to shut the machine down before catastrophic failure occurs.
These transducers are frequently used in pairs oriented 90 apart, and can be connected to the vertical and horizontal plates of an oscilloscope to display the "orbit", or path of the journal as it migrates around in the bearing.
The frequency response of the displacement transducer extends from DC (0 Hz) to about 1000 Hz.
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