**Part 3**

**Fault Diagnosis and Monitoring** 

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Calgary, AB, Oct. 2009.

**13** 

*Greece* 

**Utilising the Wavelet Transform** 

**A Review with Applications** 

Theodoros Loutas and Vassilis Kostopoulos

*University of Patras, Rio,* 

**in Condition-Based Maintenance:** 

*Applied Mechanics Lab, Department of Mechanical Engineering and Aeronautics,* 

Condition monitoring of machinery can be defined as the continuous or periodic measurement and interpretation of data in order to indicate the condition of an machine and determine the need for maintenance. Condition monitoring thus is primarily involved with the diagnostics of faults and failures and aims at an accurate and as early as possible fault detection. It is thus oriented towards an unscheduled preventive maintenance plan with continuous monitoring of the machinery as opposed to scheduled periodic maintenance. The possibility of failures of course cannot be diminished, but confident early diagnosis of incipient failures is extremely useful to avoid machinery breakdown and thus ensure a more cost-effective overall operation reducing equipment down-times. Industrial safety is also enhanced as catastrophic events are

When faults occur in machines, phenomena like excessive vibration and/or noise, increased temperatures, increased wear rate, etc. are observed. The concept is to monitor, continuously or periodically, these dynamic phenomena utilizing one or more sensors to capture this behavior. One of the earliest approaches was the sound emission monitoring. An expert human ear played the role of the sensor in the early applications, a sophisticated microphone can play the same role today. The most classic approach –widely used until the present- is the vibration monitoring with few or several accelerometers placed upon the machine. The principle is that when damage occurs, the signature of the vibration response changes in the frequency domain, giving a qualitative indication of fault existence. The Acoustic Emission (AE) technique, famous for its sensitivity in the high frequency domain of micro-damage evolution, has found important applications in gearboxes and bearings as Section 4 presents. Other monitoring techniques include oil condition monitoring (oil debris, oil conductivity or humidity etc.), current and voltage transients monitoring in electric motors as well as temperature measurements/thermography. More than 80% of the applications presented in Section 4 involve vibration monitoring, with AE finding more and more applications the last 15 years and current/voltage measurements being always an option in electric machines. Monitoring generally results in a large number of complex signals with valuable diagnostic information hidden under noise or other irrelevant sources. Over the years and the same time with several breakthroughs in the signal processing field, engineers and researchers realized

avoided when a maintenance-for-cause plan is followed.

**1. Introduction** 
