Magnetoelastic Viscosity Sensor for On-Line Status Assessment of Lubricant Oils

The actual trend in the field of maintenance in mechanical and electrical machinery, points towards the implementation of the so-called proactive maintenance. In this framework, different parameters of the system are monitored so that the current health state of the machinery can be precisely known. The health state of the lubricating oil is within the set of parameters that are to be monitored. Nearly 40% of the total reported malfunctions in heavy machinery are due to failures in lubrication. Among the different parameters that define the state of lubricant oil, viscosity is one of the most important. Lubricant oil prevents moving parts to get into direct contact so, inadequate viscosity may cause malfunctioning and even a fatal breakdown. Besides, the monitoring of the viscosity can help establishing the state of degradation of the lubricating oil. Magnetoelastic sensors based on the magnetoelastic resonance phenomena have been shown to be useful in the determination of viscosity. In this work we describe an experimental prototype to determine the viscosity of lubricant oils using the magnetoelastic resonance. The measurements are done using different commercial oils with viscosities ranging from 32 to 326 cSt. The amplitude of the resonance and the value of the resonance frequency are shown to correlate satisfactorily with the viscosity of the measured oil, demonstrating the possibility of developing a working real-time, on-line viscosity sensor based on this principle. We also show how the temperature effects on viscosity can be taken into account.