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Contents: 1. Reduce Cost 2. Increase Revenue 3. Increase Safety 4. Rduce Downtime 5. Improved Fleet-Wide Decision Support This is intended to be an overview of Prognostics Health Management (PHM) benefits; there are many more benefits than are listed here however these provide a base set of benefits that a PHM system can offer. This will help anyone that is new to PHM to understand what a PHM can do you. This can also help PHM developers to take a step back and think what are we really trying to offer by employing a PHM system? 1. Reduce Cost One of the benefits to having a PHM system will be the reduced cost to maintain the system. Maintenance costs of complex systems can be extremely large, especially for a fleet of systems. PHM provides savings through a couple of different channels; the first is through Condition Based Maintenance practices and the second is through a more automated maintenance and logistics support system. Both of these concepts will be described in more detail below: - Condition based maintenance (CBM): Condition based maintenance is a new train of though, a step forward from preventative maintenance, and significantly better than corrective maintenance. Instead of relying on system reliability information to pick the best time to perform periodic maintenance intervals, a CBM system will rely on maintenance to be performed when the system needs maintenance. A quick and simple example would be changing oil in your car. The old philosophy is to change your oil at a specific period, every 3-5k miles; this is an example of a periodic maintenance task. How a CBM system would work for this same maintenance action is by continuously reading the health of the oil and performing maintenance when it is needed based on the sensor readings. PHM enhances this sensor reading by predicting what the health of the oil will be in the future instead of only reporting the current reading. http://www.phminfo.com/images/cbm.jpg Figure 1: Condition Based Maintenance Cost Reduction Figure 1 shows a detailed explanation of cost associated with failures and maintenance in a system. Let’s break this down and understand each of the lines and what they mean. First is the blue line labeled maintenance costs, this is intended to be the cost of performing maintenance compared to the total number of failures that occur in the system. This means that if you were to spend a ton of money and change your oil every day, you would have a smaller number of failures than if you were to spend no money and never change your oil which would result in many more failures. This blue maintenance costs line is inversely related to the red cost of failure line. As you spend less money on maintenance, you will spend more money on all of the unexpected failures that happen as a result of not performing any maintenance. The sum of these two costs is depicted as the black total cost line; this is the total cost to keep your system running for the number of failures that happen. The “optimal maintenance time” is the time to perform maintenance so that together the failure cost and maintenance costs are the lowest. This optimal maintenance time can be achieved by allowing a CBM system identify components that need to be maintenance. - Enable autonomic logistics An automated maintenance and logistics system can be built around good PHM technologies. This automated logistics system will allow for a more just-in-time maintenance environment where spare parts can be ordered when they are needed, maintenance personnel can be deployed early instead of after a catastrophic failure has occurred. This overall automation of the logistics system will realize more cost savings for increasingly complex support systems such as military maintenance. The F-35 Lightning II aircraft had PHM build into it and will leverage the benefits of an autonomic logistics system. 2. Increase Revenue There are many ways that a PHM system can help to increase the revenue stream of a business. These are generally different for each implementation of PHM so I can not give a generic explanation like CBM, however I can provide specific examples of how PHM can be used to increase revenue. - Wind Generation Example Wind turbines are passive systems used to generate energy from the wind that runs over their blades. These systems depend on the wind that is available in a specific area, thus the trick is to pick an area that has a large amount of wind over a long period of time. Because these environments don’t always exist, wind turbines are generally placed in areas that have different wind profiles throughout the year, an example of one of these profiles is shown in Figure 2. http://www.phminfo.com/images/Seasons.jpg Figure 2: Wind as a function of yearly seasons Figure 2 shows the amount of wind available as a function of the yearly seasons, this shows that in season 2 there is significantly more wind than in the other seasons, which in turn means that it is extremely important for these wind turbines to be operation during season 2. On the other hand the cost of inspecting a large number of turbines prior to season 2 is insurmountable. Thus the quandary, I need the wind turbines to work, but I can’t afford to inspect them all. The solution the above stated quandary is obviously PHM. Continuously monitoring the wind turbines and predicting their health during season 2 will empower the wind turbine owner to maintain the turbines that will break and therefore increase his revenue during the high wind season 2. - Sell more reliable products If a product seller can offer a more reliable product to their customers, they will be able to gain a larger market share and therefore increase revenue. There are also many advantages for a supplier that offers warranties and product maintenance, these advantages will depend on specific situations, use your imagination. 3. Increase Safety The cost benefits are not the only important benefits of a PHM system, another potentially more important is the increased safety gained by using a PHM system. - Predict/Prevent Catastrophic Failures A PHM system will predict failures of critical system components, this prediction of failure can be used to shut down or reconfigure a system to properly accommodate the fault of provide an orderly shut down before a catastrophic failure happens. I’m sure you can envision many products in which this could be useful, my primary experience is Aircraft so I will use an aircraft example. Lets say the periodic maintenance interval for an engine is X number of hours, this airplane is flying for the next two weeks and will accumulate X-60 hours, so the engine will not be maintained in the next 2 weeks. And while flying a small problem has occurred (Incipient Fault), this fault is detected by the PHM system and is predicted to cause major functional failure in X-70 hours, within the next two weeks prior to engine maintenance. This PHM system potentially saved the plane from losing and engine in the middle of flight. 4. Reduce Downtime How useful a system is can often be associated with the amount of system downtime, along with unexpected downtime. Reducing the amount of total downtime will ultimately increase how much output can be obtained by a system and how often this output can be expected. - Opportunistic maintenance One of my favorite examples of decreasing downtime is seen in the manufacturing industry, specifically printing presses. The printing press is fed thousands of sheets of paper, much more than you conventional printer but in a similar fashion. Once all of the paper has been fed through the system the printing press need to be reloaded (15-20 minutes) also when reconfiguring the system for a new printing cycle the printing press could be down for a larger amount of time (1 hour). Let’s look at this unfortunate scenario: The printing press is brought down for a reconfiguration (1 Hour) after the system is back up and running on the new job it breaks down after 200 cycles, the system then has to go down for unexpected maintenance. This is unnecessarily increases downtime because the failure was not known earlier. Perfect opportunity for a PHM system. Now let’s suppose we have a PHM system on this printing press, before the 1 Hour scheduled reconfiguration occurs the PHM system declares a fault will bring the system down in 300 cycles. Now the maintenance team knows there is a failure in the printing press they can maintain the system during the original 1 hour downtime instead of the unexpected downtime after the reconfiguration is complete. 5. Improved Fleet-Wide Decision Support When PHM is employed on a large number of systems (Fleet), there are many more benefits that just multiplying the benefits for an individual system by the number of systems in the feet. PHM systems will provide detailed insight into the operation of every single component of the fleet; therefore specific decisions can now be made in a variety of different situations. Where and when to deploy maintenance personnel, how many spare parts do I need on hand, and where to perform opportunistic maintenance are only a few of the many fleet-wide benefits. Optimization techniques applied to the fleet wide decisions can only help to realize greater overall system benefits of employing PHM Now that you know all about the benefits of PHM look through the rest of this site and identify how you can implement a PHM solution for your system.
Article Source: http://www.e-learnet.org
Phillip Gurbacki is the owner and operator of www.phminfo.com, a Prognostic Health Management (PHM) user community sharing PHM information and discussing related topics. Phillip has a tremendous amount of experience in the PHM industry and currently assists companies with PHM development and training, helping companies begin to employ PHM technologies on their products quickly and efficiently.
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