LEO Approach

The LEO approach has been put forth by Briton as a simple formalized way of selecting the appropriate technique by assessing effectiveness. Three separate factors are considered and then combined to provide a measure of the size of the fault that must be detected for the technique to be effective.

• L: Level of critical parameter such as shocks/vibrations
• E: Experience Factor
• O: Operation Efficiency Factor

 (1) The critical parameter size, L is the cause of the particular failure being considered. In the context of cracks this could be the crack depth. If the failure were seizure of a rolling bearing it is unlikely that the size of the damage in the races could be considered. More appropriately it could be correlation between vibration and shock pulse level and occurrence of seized bearings. Thus, L, would be the vibration/shock level at which experience as shown the bearing will seize.

 (2) The experience factor, E to take account of :

• The amount of knowledge possessed of the cause and mechanism of the failure.
• The rate of progression of the failure in relation to monitoring frequency.
• Both these points of experience amount to a measure of extent of previous trouble encountered.

 (3) The monitoring operational efficiency factor, O which takes account of :

• The sensitivity and reliability of the method and equipment in relation to the characteristics of the machine and its environment, and
• The skill of the monitoring personnel

O would vary from one where failures had been thoroughly monitored, to zero where it had never been possible to detect the fault in the past.

The product L × E × O provides a measure of the monitored parameter level or change which the monitored technique must be able to detect to be certain of providing sufficient warning of impending failure. Unfortunately, although data have been collected for NDT applications the approach has not yet been taken up for general CM and no exact information is available on L, E or O factors applicable to behaviour, wear debris or vibration monitoring. However the maintenance engineer will find it useful to develop his own factors for the technique he has yet had.