Eddy Current Application Within Condition Monitoring
The Basics
At its core, an eddy current is a circulating flow of electric current induced within a conductor when exposed to a changing magnetic field. Picture a metal object moving within the influence of a magnetic field—this dynamic interplay is where the magic begins.
Applications
Eddy current technology has been widely deployed in a variety of applications, including non-destructive testing, induction heating, magnetic braking systems, proximity sensors and displacement measurement, eddy current clutches and brakes, exercise equipment, and much more.
Condition Monitoring
Eddy Current Probes, also called Inductive Proximity Probes, are non-contact displacement sensors used to determine the absolute displacement between the tip of a sensor and a conductive target material. These probes use the fluctuations induced in an electromagnetic field generated by the probe system to determine the bearing shaft position relative to the bearing casing and the dynamic vibration of the rotating shaft. Industrial Proximity Probes are most commonly used in petrochemical and energy production, specifically in turbines and reciprocating compressors that utilize journal bearings. 
A PRO Line 8 mm Proximity Probe and Driver
Proximity Probes can provide very accurate information on the position and vibration of the journal bearing shaft relative to the rest of the machine housing. For typical radial condition monitoring applications, two probes will be mounted perpendicular to the shaft 90° apart from one another to measure the X and Y axes. The vibration of the shaft will be measured as a variable DC voltage that simulates an AC vibration signal.
Using this position/vibration data from both axes, analysts can create an orbit that can be used to measure the total vibration of the shaft’s centerline as it rotates in the bearing sleeve. An orbit will provide the peak-to-peak displacement and direction of the vibration relative to the shaft centerline. The location of the shaft centerline within the bearing sleeve can also be measured with radially mounted probes. The DC portion of the voltage signal is proportional to the space between the probe tip and shaft surface. This measurement is critical in knowing the location of the shaft within the bearing housing and preventing metal contact between the shaft and bearing sleeve which could have catastrophic results.
