| | AUGUST 20238CIOReviewIN MY OPINIONCondition monitoring sensors provide data on machine conditions, always keeping operators informed and allowing them to plan repairs and perform preventive maintenance.The P-F curve is often mentioned in condition monitoring and predictive maintenance discussions where "P-F" refers to the interval between the detection of a potential failure (P) and the occurrence of a functional failure (F). It shows the different stages of an asset's life, how failures progress, and how and when different symptoms emerge which might signal impending (or actual) failure.At first, performance degradation is minor and may not require significant action. As time progresses, the potential failure indicators become stronger and more easily detectable, and the performance degradation becomes more severe, eventually ending in catastrophic failure.The timeline is split into three domains:· Proactive domain with activities including designing for reliability, precision installation and alignment, and life cycle asset management. · Predictive domain in which timely action may be taken to prevent failure or replace failing equipment before catastrophic failure occurs.· Fault domain when symptoms indicate immediate action is necessary to address occurring or inevitable failure.During these domains, different indicators/symptoms emerge. Ultrasonic, vibration and oil analysis often signal problems early; then temperatures rise and noises emerge a bit later; and finally, parts come loose and more severe damage occurs. Depending on the asset, other indicators may be shown by activities including corrosion monitoring, motor current/power analysis and process parameter trending (e.g., flows, rates, pressures, temperatures, etc.).By analyzing which symptoms of failure are likely to appear in the predictive domain for a given piece of equipment, you can determine which failure indicators to prioritize in your own condition monitoring and predictive maintenance discussions. In general, the goal is to maximize the P-F interval, which is the time between the first symptoms of impending failure and the functional failure taking place. In other words, you want to become aware of an impending failure as soon as possible to allow more time for action. This, however, must be balanced with the cost of the methods of prevention, inspection, and detection.Cost-benefit tradeoffsThere is a trade-off between the cost of systems to detect and predict the failures and how soon you might detect the condition. Generally, the earlier the detection/prediction, the more expensive it is. However, the longer it takes to detect an impending failure (i.e. the more the asset's condition degrades), the more expensive it is to repair.Every asset will have a unique trade-off between the cost of failure prevention (detection/prediction) and the cost of failure. This means some assets probably call for earlier detection methods that come with higher prevention costs like condition monitoring and analytics systems due to the high cost to repair (see the Prevention-1 and Repair-1 curves in the Cost-Failure/Time chart). And some assets may be better suited for more cost-efficient but delayed detection or even a "run-to-failure" model due to lower cost to repair (the Prevention-2 and Repair-2 curves).There are four basic maintenance approaches:ReactiveThe Reactive IDENTIFYING EQUIPMENT FAILURES BEFORE THEY OCCURBy Tom Knauer, Business Strategy Manager for Assembly, Robotics & Automation, Balluff worldwideTom Knauer
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