Introduction to Condition Monitoring
Condition monitoring and diagnostics of machines – according to ISO, Sub-committee 9ISO/TC/108/SC5. The scope of this Sub-committee – Standardisation of the procedures, process and equipment requirement uniquely related to the technical activity of condition monitoring and diagnosis of machines in which selected parameters associated with an operating are periodically or continuously sensed, measured and recorded for interim purpose of reducing, analysing, comparing and displaying the data and information so obtained and for the ultimate purpose of using this results to support decisions related to the operation and maintenance of the machine (Rao, B.K.N.).
Condition monitoring attempts to detect symptoms of eminent failure and approximates time of a functional failure. It utilises a combination of techniques to obtain the actual operating condition of the machines based on collected data such as vibration analysis, oil and wear debris analysis, ultrasound, temperature and performance evaluation. The specific techniques used depend on the type and operation of the machines.
Examples condition monitoring techniques (Scheffer and Gridhar):
(a) Vibration monitoring – this is the most commonly used and effective technique to detect internal defects in rotating machinery.
(b) Acoustic emission monitoring – this involves detection and location of cracks in bearings, structures, pressure vessels and pipelines.
(c) Oil analysis – lubrication oil is analysed and the occurrence of certain microscopic particles in it can be connected to the condition of bearings and gears.
(d) Particle analysis – worn machinery components, whether in reciprocating machinery, gearboxes or hydraulic systems, release debris. Collection and analysis of this debris provides vital information on the deterioration of these components.
(e) Ultrasonic monitoring – this is used to measure thickness of corrosion or crack on pipelines, offshore structures, pressure vessels.
(f) Thermography – this is used to detect thermal or mechanical defects in generators, overhead lines, boilers, misaligned coupling and cell damage in carbon fibre structures on aircrafts.
(g) Performance monitoring – this is used to determine the performance problems in equipment. The efficiency of machines provides a good inside on their internal conditions.
