Robert S. Blakeney, Bonner & Moore Associates, Inc., Houston, Texas

Implementing a computerized maintenance management system takes many hours of preparation and data loading before any value can be measured. One of the biggest data entry jobs is entering the information needed to drive preventive maintenance schedules. Entering the initial information for plant functions, processes, assets and components is no small task, and this is just the first step. Triggers for preventive maintenance routines need to be entered as well. To maintain the process, operational data must be gathered on these items and entered throughout their lives. This is equally time consuming and typically takes a person or group of people dedicating part or all of their time to gathering the information and entering data at the keyboard.

This data entry process introduces the possibility for error and increases labor costs. But there is a way to reduce these costs and eliminate the error: integrate your computerized maintenance management system with equipment monitoring systems. These systems are already capturing most of the data your computerized maintenance management system needs to trigger preventive maintenance routines; you just need to tie the two together. Here are three basic preventive maintenance triggers and how two of them can be entered and maintained automatically by equipment monitoring systems.

Preventive and predictive maintenance triggers
When establishing routines for maintenance, there are three basic types of trigger criteria: time-based; usage-based; and condition-based. Time-based triggers are used for preventive maintenance. Usage- and condition-based triggers can readily accept the information captured by equipment monitoring systems. Condition-based triggers are needed to move your organization towards predicting failure or predictive maintenance. Take note, your computerized maintenance management system must support usage- and condition-based triggers to take advantage of integration. If it doesn't, it will need to be modified or replaced.

Time-based triggers.
Although time-based triggers don't lend themselves to integration, a description is appropriate to establish a basis for comparison. As the simplest form of trigger, time- or calendar-based triggers generate a predefined job plan or routine based on a static or dynamic point in time. This is the basic trigger criteria provided by even the most rudimentary computerized maintenance management systems for preventive maintenance. It can be "do this job every 30 days" or "perform this inspection on the 15th of every month." You enter the criteria needed for generating preventive maintenance work orders based on company policy, manufacturer's recommendations, or gut feel based on experience.

A static timing trigger doesn't take into account the date and time when the last job was completed, so the computerized maintenance management system just keeps generating the preventive maintenance at the specified time regardless of when you last did the work. This can be extremely wasteful and can push you into performing more maintenance than is necessary.

Dynamic timing calculates the next preventive maintenance generation based on the last time you completed the job. If you were five days late in getting the work completed, the computerized maintenance management system adds five days and then recalculates the next preventive maintenance generation. This is a bit better than static timing for you are at least performing the maintenance as outlined by internal policy or manufacturer. It's still not the best because the amount of maintenance performed is arbitrary. You still could be performing too much maintenance and you can miss a complete maintenance cycle to the cumulative affect of the timing.

Usage-based triggers.
Usage-based triggers such as gallons pumped, hours operated, elapsed time, miles driven, and so on are better triggers because they help you drive maintenance activities based on operations. These do require data entry to update the preventive maintenance calculations. For example, a preventive maintenance routine to check the seals in a pump can be based on operating hours. You establish the trigger "do this predefined job plan every 1,000 hours of operation" and then enter the first trigger so the computerized maintenance management system knows where to begin. From then on, you must periodically capture clock readings--a predefined work routine itself--and enter them into the computerized maintenance management system. When the hours accumulated reach the 1,000 hour threshold, out comes the preventive maintenance work order.

Problems can arise, however, when readings aren't captured in a timely fashion or an error is made at the time of the reading or during keyboard entry into the computerized maintenance management system. Adding an extra zero to a meter reading can really make your day. Imagine getting the preventive maintenance work orders on an asset between 1,000 and 10,000 clicks all at once. Besides being a nuisance, this kind of error lowers staff confidence levels in the computerized maintenance management system and can erode overall system usage.

You can eliminate these problems by integrating with a monitoring system that is already capturing meter readings. The possibility for data error is almost nil and you've eliminated both the need to gather the data and to manually enter it. That's labor time that can be applied to something else. This type of trigger is better than time-based triggers and can be adjusted based on actual, real-world experiences.
 

For example, if you are capturing failure data of components or parts by manufacturer, then it becomes easy to compare brands and adjust the time to replacement based on usage. Plotting failure rates for a type of seal by brand shows you which brands last longer. Brand X may require replacement at 1,000 clicks but brand Y lasts 1,200. You can then adjust preventive maintenance cycles accordingly.

This can also provide you with the ammunition you need to justify a more expensive part over another because you can show extended life, fewer failures, and less maintenance. In addition, the maintenance function is driving the usage and stocking levels of spares based on real operations data, not on someone's best guess. Usage triggers are better than time-based triggers, but basing preventive maintenance routines on actual equipment condition is better.

Condition-based triggers.
Condition-based triggers include vibration readings, temperatures, pressures and particle concentrations. Most of these can also be monitored by equipment systems using accelerometers, temperature and pressure sensors. These are more sophisticated methods for monitoring real-time data and are ideal for triggering preplanned jobs.

Vibrations, for example, are typically monitored by sensors attached directly to an asset and when a peak vibration threshold is reached, an alarm is sounded. Operations staff then know there is a problem. And if there is a problem, who fixes it? Maintenance, of course!

Ideally, the monitoring system should generate a message to the computerized maintenance management system simultaneously with the operations alarm and then the computerized maintenance management system would generate a preplanned inspection routine or other job or, in the case of a more modern computerized maintenance management system, an e-mail message. The maintenance staff becomes as informed as operations and can respond in a timely fashion, work plan in hand. In some cases, the equipment monitoring system can automatically have the equipment powered down before the work crew arrives.

Another feature of some monitoring systems is that they can also gather vibration readings throughout a time period. These automatic readings replace the inspection readings that are gathered manually by maintenance personnel. An interface from the monitoring system to your computerized maintenance management system automatically populates the database. Don't let operations hoard this data, it's too valuable. You can eliminate real labor hours through an interface like this.

Condition-based maintenance can be the best way to schedule preventive maintenance because the asset itself is telling you when to do the work, not some arbitrary time period established by company policy or manufacturer. If you couple this with past performance trends, you can move into predicting breakdowns and begin to operate equipment right up to failure with more confidence. This is the best way to gain the most value from your assets.

Be aware, however, that automatically monitoring every asset is not cost effective. Putting sensors on all equipment simply costs too much. Choose only those systems, processes, assets or components that are critical to your operations and compare the criticality to the cost of automation.

Summary
Performing preventive maintenance routines based on arbitrary rules does not support you in the ultimate goal of reducing maintenance. Manually entering real data so you can base preventive maintenance on non-arbitrary triggers helps reduce overall maintenance costs but involves a trade-off in time and manpower. You can reduce these costs and improve your preventive maintenance and predictive maintenance program simultaneously by integrating your computerized maintenance management system and an equipment monitoring system. This is a logical blend of operations control and maintenance management that will reduce work load, eliminate data entry error, and help you move to a more condition-based maintenance program.