Condition monitoring is the process of monitoring a parameter of condition in machinery, such that a significant change is indicative of a developing failure. It is a major component of predictive maintenance. The use of conditional monitoring allows maintenance to be scheduled, or other actions to be taken to avoid the consequences of failure, before the failure occurs. It is typically much more cost effective than allowing the machinery to fail. Serviceable machinery include rotating machines and stationary plant such as boilers and heat exchangers.

Rotating machinery

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The most commonly used method for rotating machines is called vibration analysis. Measurements are taken on machine bearing casings, and on some machines, on the rotating shafts. The level of vibration can be compared with established standards to assess the severity.

Usually a full spectrum of the vibration is sampled, and using fast Fourier algorithms the component frequencies and their accelerations may be determined. Analysing the frequencies and their harmonics helps locate the root cause of the vibration, allowing it to be remedied, and hopefully designed out. For example, high vibration at the frequency corresponding to the speed of rotation is usually due to unbalance.

Handheld data collector and analysers are now commonplace. The technician can collect data samples from a number of machines, then download the data into a base computer, which compares the latest sample with the previous ones and shows up any change.

Degrading rolling element bearings give out increasing vibration signals as they wear. Special analysis instruments can detect wear even months before failure, giving ample warning to schedule replacement.

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Other techniques

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• Slight temperature variations across a surface can be discovered with visual inspection and nondestructive testing with thermography. Heat is indicative of failing components, especially degrading electrical contacts and terminations.
• Using a Scanning Electron Microscope of a carefully-taken sample of debris suspended in lubricating oil (taken from filters or magnetic chip detectors). Instruments then reveal the elements contained, their proportions, size and morphology. Using this method, the site, the mechanical failure mechanism and the time to eventual failure may be determined.
• Performance analysis, where the physical efficiency, performance, or condition is found by comparing actual parameters against an ideal model. Deterioration is typically the cause of difference in the readings.

Condition-Monitoring

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