As the new data is added, the computer checks against the limits, and flags any results that fall outside them. However, checking against pre-set limits is not enough. It is apparent that even when the general wear levels, or limits, are known for a unit type, there will always be odd units which run well below the norm. These units can undergo deterioration without exceeding limits, and consequently there is a continuous monitor for the rate of change from the previous levels for each unit.
Analysis of proportions of elements
A single element out of limits is not necessarily an indication of a serious defect, even when the limit has been greatly exceeded.
Many engineering materials contain a high proportion of a common element [such as iron] combined with much smaller proportions of other elements [molybdenum, chromium, nickel, etc.]. As the ratio of the main element to the secondary element may be in the order of 20:1, a failure which produces for example 4 parts per million [PPM] could be expected to produce only 0.1 or 0.2 PPM of a secondary element.
Modern low level detection therefore allows the examination of the Ôsecondary' elements which can give valuable aid in deciding how serious the problem really is. The programs have been developed to check the relative proportions of the main and secondary elements to determine the likely source material.
A variety of reports are available, each specifically designed to provide quick and easy assimilation of results.
The data is presented both in its numerical and graphical form. The graphical section is selective, reflecting those elements which are considered to be relevant to the particular unit.
The program identifies results which fall outside the limits for that unit or have changed from the previous results by more than a specified amount.
The graphical section makes it possible to recognize simultaneous shifts in the results for several elements and the combinations of elements can give very important clues to the underlying causes. This form of print-out is particularly valuable to operators of large fleets because results for a large number of engines can be scanned in a very short time and any units which deserve more concentrated attention can be identified.
This type of report allows easy assessment of an entire fleet as opposed to a single unit. All the current results for a single element and for all units in the fleet are presented on a single report. This makes it very easy to determine which results are normal for that type of unit and at what stage the results require further investigation.
Particles that are collected on magnetic chip detectors, backflushed from filters or filtered from an oil sample can be analyzed using a scanning electron microscope (SEM).
The SEM provides both a visual assessment and an analysis of the composition of the debris. Visual assessment is made possible by magnifying the particle up to 200,000 times; a far greater resolution than that provided by an optical microscope. From the appearance of the particle it might be possible to determine its origin and whether it has suffered abrasion from other components. A plot is displayed on screen which details the constituent elements of the particle to enable identification of its source. Imaging software now enables operators to receive a printed colour image of the debris that has been analyzed.
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