http://en.wikipedia.org/wiki/Condition_Based_Maintenance

Overview
Breakdowns in industrial manufacturing systems can have significant
impact on the profitability of a business. Expensive production
equipment is idled, labor is no longer optimized, and the ratio of
fixed costs to product output is negatively affected. Rapid repair of
down equipment is critical to business success; the process of
addressing equipment breakdowns after occurrence is known as
Corrective Maintenance and exists in some form in all manufacturing
companies. However, when equipment breakdowns occur the cost can go
well beyond the period of repair. Often process lines require
significant run-time after startup to begin producing quality
product, and the manufactured goods in process at breakdown as well
as the goods manufactured for a period after breakdown may either be
usable or of less value. Because of the impact both during and beyond
the immediate downtime, businesses have sought to prevent equipment
breakdown by a process known as Preventative Maintenance. With
preventative maintenance equipment is routinely inspected and
serviced in an effort to prevent breakdowns from occurring. Such
inspections are based on either calendar periods or equipment process
time, and generally include recorded data that can be compared over
time to determine if negative shifts indicate an imminent equipment
problem.

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Läs på. Göran Wikingson CBM-Sweden