Determining inductive sensor wear debris limits for rolling contact fatigue of bearings

A relatively recent development for the condition monitoring of oil-wetted machinery has been the in-line full-flow inductive wear debris sensor (hereafter referred to as inductive wear debris sensors). These sensors detect a disturbance to a magnetic field caused by metallic wear debris shed from deteriorating dynamic components that is entrained in the lubricant. Applications for these sensors currently include (but are not limited to) aviation machinery, wind-turbine generators, marine propulsion systems, and locomotives. Inductive wear debris sensors can distinguish between ferromagnetic and nonferromagnetic particles as well as providing size and other related information. One of the primary advantages of this sensor type is that the detectable size range is broad and may be used to track the progress of an incipient failure such as the rolling contact fatigue of a bearing or gear as it occurs. One aspect that has received little attention in the literature is the methodology for determining a suitable limit for a particular application. Limits are a critically important aspect of machinery condition monitoring and need to be established by a robust and reliable method otherwise unnecessary maintenance can occur or an incipient fault may be missed. This paper describes a generic method for determining a physically meaningful debris limit for a deteriorating rolling element bearing when utilizing an inductive wear debris sensor.