maintenance work b.b

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Maintenance is the combination of all technical and associated administrative actions

intended to retain an item in, or restore it to, a state in which it can perform its required

function. Many companies are seeking to gain competitive advantage with respect to

cost, quality, service and on-time deliveries. The effect of maintenance on these

variables has prompted increased attention to the maintenance area as an integral part

of productivity improvement. Maintenance is rapidly evolving into a major contributor

to the performance and profitability of manufacturing systems. In fact, some see

maintenance as the "last frontier" for manufacturing.

In their article "Make Maintenance Meaningful" P.K. Kauppi and Paavo Ylinen describe

the bulk of maintenance procedures as being as:

y Preventive maintenance²the prevention of equipment breakdowns before they

happen. This includes inspections, adjustments, regular service and planned

shutdowns.

y R epair work²repairing equipment and troubleshooting malfunctions in an effort

to return the equipment to its previous condition. These repairs may be reactive

or preventive.

y Improvement work²searching for better materials and improved design changes

to facilitate equipment reliability. R epair work is often a part of improvement

work.

As shown in Figure 1, six maintenance programs are identified within the maintenance

hierarchy, each representing an increased level of sophistication.

Figure 1

Maintenance Hierarchy



REACTIVE M AINTENANCE

R eactive maintenance (also known as corrective maintenance) involves all unscheduled

actions performed as a result of system or product failure. Basically, it is an attempt to

restore the system/product to a specified condition. The spectrum of activities within

this level are (1) failure identification, (2) localization and isolation, (3) disassembly, (4)

item removal and replacement or repair in place, (5) reassembly, and (6) checkout and

condition verification. This approach is mainly a response to machine breakdowns.

Unfortunately, many manufacturers are still in a reactive mode of operation. Their main

objective is to ship the product. If their manufacturing equipment breaks down, they fix

it as quickly as possible and then run it until it breaks down again. This is an extremely

unreliable process and is not the best way to maximize the useful life span of one's

assets. It leaves machine tools in a state of poor repair and can cause the production of

out-of-tolerance parts and scrap. Because of its unpredictable nature it can easily cause

disruptions to the production process.

SCHEDULED M AINTENANCE

Scheduled maintenance utilizes a previously developed maintenance schedule for each

machine tool. This is much like an oil change on an automobile that takes place every

three months or 3,000 miles, whichever comes first. While this is a broadly practiced

technique in many manufacturing organizations, it does possess some distinct

disadvantages. The scheduled maintenance may take place too soon, while the machine

still operates well (15-20 percent of all components fail after a predictable time), or it

may come too late if the machine fails before the scheduled maintenance time. In some

cases, the machine may still be running but producing unacceptable parts. Scheduled

maintenance can be considered a part of preventive maintenance known as fixed-time

maintenance (FTM). Preventive maintenance is discussed later.

PREDICTIVE M AINTENANCE

Predictive maintenance involves performing maintenance on a machine in advance of

the time a failure would occur if the maintenance were not performed. Of course, this

means that one must calculate when a machine is predicted to fail. In order to do this,



the firm must collect data on variables that can be used to indicate an impending failure

(vibration, temperature, sound, color, etc.). This data is then analyzed to approximate

when a failure will occur and maintenance is then scheduled to take place prior to this

time. By seeking the correct level of maintenance required, unplanned downtime is

minimized.

PREVENTIVE M AINTENANCE

Preventive maintenance encompasses activities, including adjustments, replacement,

and basic cleanliness, that forestall machine breakdowns. Preventive activities are

primarily condition based. The condition of a component, measured when the

equipment is operating, governs planned/scheduled maintenance. Typical preventive

maintenance activities include periodic inspections, condition monitoring, critical item

replacements, and calibrations. In order to accomplish this, blocks of time are

incorporated into the operations schedule. One can easily see that this is the beginning

of a proactive mode rather than a reactive one. The purpose of preventive maintenance

is to ensure that production quality is maintained and that delivery schedules are met.

In addition, a machine that is well cared for will last longer and cause fewer problems.

Current trends in management philosophy such as just-in-time (JIT) and total quality

management (TQM) incorporate preventive maintenance as key factors in their success.

JIT requires high machine availability, which in turn requires preventive maintenance.

Also, TQM requires equipment that is well maintained in order to meet required process

capability.

Preventive maintenance is also seen as a measure of management excellence. It requires

a long-term commitment, constant monitoring of new technology, a constant

assessment of the financial and organizational tradeoffs in contracting out versus in-

house maintenance, and an awareness of the impact of the regulatory and legal

environment.

The resulting benefits of preventive maintenance are many. Some of them are listed

below:



y Safety. Machinery that is not well-maintained can become a safety hazard.

Preventive maintenance increases the margin of safety by keeping equipment in

top running condition.

y Lower cost. A modern and cost-effective approach to preventive maintenance

shows that there is no maintenance cost optimum. However, maintenance costs

will decrease as the costs for production losses decreases. Obviously, no

preventive maintenance action is performed unless it is less costly that the

resulting failure.

y R eduction in failures and breakdowns. Preventive maintenance aims at reducing

or eliminating unplanned downtime, thereby increasing machine efficiency.

Downtime is also reduced when the preventive maintenance process gives

maintenance personnel sufficient warning so repairs can be scheduled duringnormal outages.

y Extension of equipment life. Obviously, equipment that is cared for will last

longer than equipment that is abused and neglected.

y Improved trade-in/resale value of equipment. If the equipment is to be sold or

traded in, a preventive maintenance program will help keep the machine in the

best possible condition, thereby maximizing its used value.

y Increased equipment reliability. By performing preventive maintenance on

equipment, a firm begins to build reliability into the equipment by removing

routine and avoidable breakdowns.

y Increased plant productivity. Productivity is enhanced by the decrease in

unexpected machine breakdown. Also, forecast shutdown time can allow the firm

to utilize alternate routings and scheduling alternatives that will minimize the

negative effect of downtime.

y Fewer surprises. Preventive maintenance enables users to avoid the unexpected.

Preventive maintenance does not guarantee elimination of all unexpected

downtime, but empirically it has proven to eliminate most of it caused by

mechanical failure.

y R educed cycle time. If process equipment is incapable of running the product,

then the time it takes to move the product through the factory will suffer.

Taninecz found, from an Industry Week survey, that there is a strong correlation



between preventive maintenance and cycle-time reductions as well as near-

perfect on-time delivery rates. Also, approximately 35 percent of the surveyed

plants who widely adopted preventive maintenance achieved on-time delivery

rates of 98 percent, compared to only 19.5 percent for non-adopters.

y Increased service level for the customer and reduction in the number of defective

parts. These have a positive direct effect on stock-outs, backlog, and delivery time

to the customer.

y R educed overall maintenance. By not allowing machinery to fall into a state of

disrepair, overall maintenance requirements are greatly decreased.

TOTAL PRODUCTIVEM AINTENANCE

Total productive maintenance (TPM) is preventive maintenance plus continuing efforts

to adapt, modify, and refine equipment to increase flexibility, reduce material handling,

and promote continuous flows. It is operator-oriented maintenance with the

involvement of all qualified employees in all maintenance activities. TPM has been

described as preventive maintenance with these three factors added: (1) involving

machine operators in preliminary maintenance activities by encouraging them to keep

machines clean and well lubricated; (2) encouraging operators to report indications of

incipient distress to the maintenance department; and (3) establishing a maintenance

education and training program.

Developed in Japan, TPM places a high value on teamwork, consensus building, and

continuous improvement. It is a partnership approach among organizational functions,

especially production and maintenance. TPM means total employee involvement, total

equipment effectiveness, and a total maintenance delivery system. In order to achieve

this, machine operators must share the preventive maintenance efforts, assist

mechanics with repairs when equipment is down, and work on equipment and process

improvements within team activities. TennesseeEastman found that another employee,

such as an equipment operator, with minimal training, could do 40 percent of the

traditional maintenance mechanic's work. Another 40 percent could be performed with

additional training, but still below the certified level. Only 20 percent of the

maintenance tasks actually required a certified mechanic's skills. They also reported that



as much as 75 percent of maintenance problems can be prevented by operators at an

early stage. This frees maintenance personnel to be responsible for the tasks that require

their critical skills, such as breakdown analysis, overhaul, corrective maintenance and

root cause analysis. This places them in a "consultant" role with the operators allowing

them to:

y help the operator diagnose problems and restore equipment to like-new

condition;

y use appropriate technologies and standards to verify that the equipment is in

like-new condition after repair, overhaul, or replacement;

y use this knowledge to assess the root cause of the problem so that changes may

be made to the design, operation, or maintenance practices in the future;

y work with purchasing, engineering, operations, and maintenance to modify

procurement standards to assure maximum reliability in future equipment.

Of course, for all of this to work, the firm must have an organizational culture which

supports a high level of employee involvement. Businesses must be willing to provide

the necessary training in order to allow production personnel to perform the required

tasks.

TPM's focus is on elimination of the major losses or inefficiencies incurred in

production activities. These losses include those due to obstruction of equipment

efficiency, manpower efficiency, and material and energy efficiency. Based on their link

to corporate goals, targets for eliminating or reducing these losses are developed. Just as

in activity-based cost accounting where cost drivers are identified, the objective of TPM

is to identify variables that can demonstrate improved performance. All major

equipment losses are functionally related to availability, performance, efficiency and/or

quality rate so the improvement resulting from the maintenance system can be

measured by its impact on overall equipment effectiveness (see below).

Beneficial results of TPM include:

y Overall equipment effectiveness and overall efficiency are maximized.



y It takes the guesswork out of determining which machine needs major repairs or

rebuilding.

y It provides objectivity by converting the operator's intuition into quantifiable

values.

y It pinpoints exact maintenance requirement. The operator carries out only the

needed corrective actions so no unnecessary work, beyond routine maintenance,

is done.

y It rapidly verifies the effectiveness of major corrective work.

y Operators improve their job skills.

y Operators are motivated by involvement in maintaining their own machines and

by involvement in team-based concepts.

y Operator involvement in the process gives them ownership of making the projecta success.

y A preventive maintenance program for the lifecycle of the equipment is

developed.

y By getting everyone involved in equipment design and selection, a better

understanding of why certain decisions and trade-offs are necessary results.

y Equipment and maintenance management (inherent in a reliability strategy)

result.

y Capacity is maximized.

y Costs are minimized.

y Product quality is improved.

y Improved safety.

y The manufacturing process is continually improved.

As a final note on TPM, another school of thought holds that TPM can be adopted by

continuous diagnostic monitoring of a machine's conditions and establishing a trend

line for it. Trend lines approaching or veering into the domain that identifies poor

operating conditions will trigger maintenance action.

RELIABILITY-CENTERED M AINTENANCE



It has been assumed that preventive maintenance programs help to ensure reliability

and safety of equipment and machinery. However, tests performed by airlines in the

mid-1960s showed that scheduled overhaul of complex equipment had little or no

positive effect on the reliability of the equipment in service. These tests revealed the

need for a new concept of preventive maintenance, which later became known as

reliability-centered maintenance (R CM).

The concept of R CM is rooted in a 1968 working paper prepared by the Boeing 747

Maintenance Steering Group. A refined version appeared in 1970. Continued studies at

the Department of Defense led to the 1986 publication of the "R eliability Centered

MaintenanceR equirements for Naval Aircraft, Weapons Systems and Support

Equipment," a set of maintenance standards and procedures that certain military

maintenance personnel were expected to follow. The R CM methodology was further

developed and found application not only in the military and aviation, but also in the

energy, manufacturing, foundry, and transport industries.

According to Bulmer, theR CM process can be considered as three separate but

associated analyses: failure mode and effects analysis, consequence analysis, and task

analysis. These analyses consider the specific characteristics and consequences of a

failure and attempt to arrive at the optimal solution based on this information.

OVERALL EQUIPMENT EFFECTIVENESS

Total productive maintenance provides a systematic procedure for linking corporate

goals to maintenance goals. This procedure calls for the consideration of external and

internal corporate environments, and then the development of a basic maintenance

policy congruent with the environments. Next key points for maintenance improvement

are identified, which result in the definition of target values for maintenance

performance. These values, referred to as overall equipment effectiveness (OEE), are a

function of equipment availability, quality rate, and equipment performance efficiency,

and provide a starting point for developing quantitative variables for relating

maintenance measurement and control to corporate strategy.



Essentially, OEE offers a measurement tool that helps identify the real areas of

opportunity within an operation. These areas have been termed the "six big losses." OEE

allows the firm to break these losses into smaller components to better evaluate the

impact the maintenance program is making on the operation. The six losses are:

1. Breakdowns from equipment failure (unplanned downtime)

2. Setup and adjustments from product changes and minor adjustments necessary

to get the equipment operating properly after the line change

3. Idling and minor stoppages due to abnormal operation of the equipment causing

momentary lapses in production, but not long enough to track as downtime

4. R educed speeds, the discrepancy between design and actual speed the equipment

operates

5. Process defects due to scrapped production and defects needing rework

6. R educed yield and lost materials during the manufacturing process, from start-

up to end of production run

If a company has an OEE of 85 percent or more, then it is considered to be a world-class

company.

TRENDS INM AINTENANCE

Two major trends in the development of maintenance management research have been

identified: (1) emerging developments and advances in maintenance technology,

information and decision technology, and maintenance methods; and (2) the linking of

maintenance to quality improvement strategies and the use of maintenance as a

competitive strategy.

The first major trend has to do with the impact of artificial intelligence techniques, such

as expert systems and neural networks, on the formation of maintenance knowledge inindustrial organizations. There is a diverse application of expert systems within the

maintenance area. A number of these systems and their applications are listed below:

y CATS²an expert maintenance system for detecting sudden failures in diesel-

electric locomotive systems



y INNATE²an expert system used for electronic circuit diagnosis

y FSM²an expert system used by Boeing for continuous condition monitoring of

aircraft alarms

y RL A²an expert system developed by Lockheed for repair-level analysis for major

parts in an aerospace system

y GEMS-TTS²an expert system used by AT&T maintenance specialists to isolate

faults in communication links

y TOPAS²an expert system that diagnoses transmission and signaling problems in

real time that may arise on switched circuits.

y CHA RLE Y²an expert system used by General Motors to diagnose problems with

broken machine tools and to instruct less experienced individuals by providing

explanationsy XCON²an expert system developed by Digital Equipment Corporation (now part

of Compaq) for product configuration

The second major trend is typified by the emergence of total productive maintenance,

which must be incorporated into the firm's strategy. In the quest for world-class

manufacturing, many industries are appreciating the need for efficient maintenance

systems that have been effectively integrated with corporate strategy. It is vital that

maintenance management becomes integrated with corporate strategy to ensureequipment availability, quality products, on-time deliveries, and competitive pricing.

Managerial attitudes have changed toward maintenance because of the emergence of

new management philosophies. In addition, social trends such as lack of capital,

fluctuations in currencies, competition, quality, and environmental consciousness, have

also encouraged a new focus on maintenance.

Maintenance will continue to be a major area of concern for manufacturers and other

forms of business. A study of some seventy manufacturing plants found that over 50percent of the maintenance work performed by these firms was reactive (run to failure,

emergency breakdown). The balance of maintenance work was preventive or period

based (25 percent), predictive or condition based (15 percent), and proactive or root-

caused based (10 percent). A strong correlation has been found to exist between

manufacturing cost reduction and preventive/predictive maintenance. Over a five-year



period a study group of companies found that productivity improvements correlated

strongly with a number of variables, one of which was preventive/predictive

maintenance.

Mike Laskiewicz recommends that organizations recognize maintenance as a key

department that needs to be well managed. In addition, the maintenance department

should be led by a strong-minded individual who is a good motivator, technically

competent, experienced and familiar with advanced industry practices. Finally

Laskiewicz notes that maintenance planning must be a top priority.

SEE AL SO: Continuous Improvement ; Lean Manufacturing and Just-in-Time

Production ; Operations Strategy ; Organizational Culture

R ead more: Maintenance - strategy, system, definition, school, model, company,

hierarchy, disadvantages, business, system, R eactive maintenance, Scheduled

maintenance, Predictive maintenance, Preventive maintenance

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Evaluating the maintenance requirement

It¶s not sufficient to evaluate only the units needing maintenance. Study the system, the workingenvironment in which the units operate and how the unit or system might affect the operation of theplant itself. Identify bottlenecks that can harm the whole system ² or the whole plant. Checkbottlenecks with extra care and evaluate their condition to ensure that no unforeseen problems canthreaten plant operation.

Keep in mind that the plant¶s designers probably didn¶t have maintenance foremost in their mind.Instead, they probably had instructions to design and build it as cheaply as possible. Also, the plantprobably was erected by workers having little knowledge about maintenance. Most plants can showhorrendous examples of the effect of this lack of knowledge. There¶s no doubt that plantmaintenance often can benefit from a bit of a redesign, an option that shouldn¶t be ruled out.

Maintenance requirements typically come in three varieties: condition-based, time-based or run tofailure. These classifications are by no means exhaustive and they¶re only meant to provideguidance when evaluating the kind of maintenance suitable for each unit evaluated.

Conditi on-based maintenance ( CBM)

This can be the most economical choice, but only if the cost of the monitoring devices isn¶t too highand extensive dismantling to check the condition of the equipment isn¶t required. CBM works bestwhen simple checks are sufficient to get an indication of the equipment¶s condition.

A simple visual inspection can detect leaks or other mechanical faults. You can use touch to detectheat and vibrations. You can listen for damaged bearings and even smell to detect overheating or oilleaks. Also, trending the recorded process variables can be used to detect the need for maintenance. However, for vital or costly equipment, use instruments because they detect faultslong before an operator can using only the five senses.

Time-based maintenance

This is the type that manufacturers normally recommended. It¶s based solely on the number of operating hours or calendar days a unit has been in operation. This method normally is used whencondition monitoring is too difficult or when there¶s a clear correlation between operating time andmechanical failure. When using time-based maintenance, consider how the unit is used. Therecommended maintenance intervals normally apply to units in fairly constant operation. It¶s notuseful for units that are mainly in standby mode.



For the latter type of equipment it¶s better to multiply the number of starts by an ³equivalent´ number of operating hours. For example, an emergency generator is tested every week (52 starts per year)and each start can be considered equal to 20 running hours. Multiplying the number of starts by 20gives a value that should be added to the true running hours to arrive at the maintenance trigger point. This method is recommended because each start causes more wear than an hour in normaloperation.

R un t o failure

This maintenance approach is used for highly reliable equipment, when it¶s difficult to performcondition monitoring or when instrumentation is costly in comparison to the equipment value.

Although not normally recommended, run to failure can be used if the unit in question won¶t interferewith plant operation should it cease to function, assuming it can be replaced easily and rapidly. If not, it might be possible to alter the installation to enable a rapid replacement. This maintenancetype can be tied to the unit ² if the unit needs to be included in the maintenance system at all.

The design of any vital system should be reconfigured if some run-to-failure component can fail often

and without warning.

Writing the pr ocedures

After the relevant data for each applicable unit has been captured and its maintenance requirementanalyzed, it¶s time write procedures. Enter them directly into the computerized maintenance systemor write them by hand on a note pad ² the important thing is to have the procedures written.

Although it¶s essential to involve plant personnel in the equipment analysis, it¶s probably unfair toforce them to enter data into the computer system. As one operator put it, ³If I wanted to sit and writeall day, I would have gotten me an office job.´ Management should consider outsourcing the initialmaintenance procedure drafting and development using a competent technical writer with

knowledge about maintenance and producing suitable procedures.

If plant personnel follow the advice given above, the result will be a valuable information resourcethat forms the basis of the comprehensive set of maintenance procedures. It would reduce the labor required to write the procedures, thus saving a substantial amount of money.

Gunnar Gustafsson is educated as a Marine Engineer with a long experience from operating and maintaining ships, oil rigs and power plants of various types, He now puts his education and experience to good use as a technical writer. Contact him at

The Maintenance Information Loop

Figure 1 below describes the flow of maintenance information and how the various aspects

fit together.



Figure 1 ± Maintenance Information Loop

The large square block indicates the steps that take place within the computerized

maintenance management system, or CMMS.

It is good practice to conduct some form of analysis to identify the appropriate maintenance

tasks to care for your equipment. RCM2 is probably the most celebrated methodology, but

there are many variations.

The analysis will result in a list of tasks that need to be sorted and grouped into sensible

chunks, which each form the content of a checklist. Sometimes it may be necessary to do

some smoothing and streamlining of these groups of tasks in an iterative manner.

The most obvious next step is to schedule the work orders generated by the system into a

plan of work for the workshop teams.

Less common, however, is to use this checklist data to create a long-range plan of

forecasted maintenance work. This plan serves two purposes:

The results can be used to determine future labour requirements, and

They feed into the production plan.

The schedule of planned jobs is issued to the workshop and the work is completed.

Feedback from these work orders, together with details of any equipment failures, is

captured in the CMMS for historical reporting purposes.

A logical response to this shop floor feedback is that the content of the checklists should be

refined to improve the quality of the preventive maintenance, especially to prevent the

recurrence of failures.



A common mistake however, is to jump straight from the work order feedback and

immediately change the words on the checklists. When this happens, the integrity of the

preventive maintenance programme is immediately compromised because the revised

words on the checklist have no defendable scientific basis. This should be avoided wherever

possible.

The far better approach to avoid this guessing game is to route all the checklist

amendments through the same analysis as was used originally to create the initial

checklists. This means that the integrity of the maintenance program is sustained over the

long term. Implicit in this approach, however, is the need to have a robust system in which

the content of the analysis can be captured and updated easily.

Finally, all the information that gets captured into the CMMS must be put to good use

otherwise it is a waste of time. This is the value of management reports that can be created

from maintenance information.

In the RCM analysis

Without describing the complete RCM analytical process, it is instructive at this stage to

point out a few details that are important to the content of such an analysis because of the

way they can impact the overall maintenance plan.

Table 1 ± Information captured in the RCM-style analysis

RCM Additional

Identify the: Functions

Functional failures

Failure modes

Failure effects

Equipment hierarchy down to

component level

Root cause of failure

Analytical tool to select: Failure effect category

Preventive/ correctivemaintenance tasks (as

appropriate)Task frequency

Crafts

Task duration

Running/stopped marker

The center column is what will be found in any typical RCM-style analysis.



In addition to that, there is value in constructing a hierarchy of the equipment system

showing assemblies, subassemblies and individual components. This helps to keep track of

which section of the system is being considered at any time, and the list of components also

helps to identify the spare parts requirements for the system.

Of vital importance is the clear identification of the root cause of each failure, as this willaffect the selection of a suitable maintenance task. To illustrate this point, consider for

example, a seized gearbox. ³Seized´ is an effect. There could be several root causes of this

failure mode that can be addressed in different ways through the maintenance program.

There is usually no value in aiming maintenance at the effect of a failure.

Also important from a planning perspective is to identify the time it will take to carry out

each task independently. The sum total of these task times gives a good indication of how

long the total work order will take.

All of the above depends on the production process and the site¶s operating context, so

these comments should be taken simply as a guideline.

The following are a few points to consider when constructing a preventive maintenance

program:

Preventive maintenance tasks must:

y aim at the failure process

y be specific

y include specifications or tolerances

Wherever possible, aim for predictive rather than preventive tasks

y measure or check for conditions against a standard

y report the results

y create a follow-on task to repair or replace at the next opportunity

³Check and replace, if necessary´ tasks destroy planned times

Frequencies and estimated times for each task must be accurate and meaningful

Try wherever possible to only plan shutdown time for ³non-running´ tasks. Keep ³running´

tasks to be done during periods of normal production. Structure the maintenance program

to allow for this.

Sorting and grouping of checklists



After analysing all the maintenance requirements for the equipment system, these

individual tasks would be grouped together to create the checklists, based on common

criteria for:

y Craft

y Frequencyy Safety / Non-safety tasks

y Running / Non-running checks and sensible

y Timing, etc. «

Smoothing the PM workload

In order to smooth the PM workload, a robust approach is to base the spread of PM

activities on the checklists arising from the RCM-style analysis. This assumes that the

analysis has been conducted thoroughly and that it is in a format that can be amended

easily.

The graph in Figure 2 below illustrates how it is possible to arrange the occurrence of the

PM work orders in such a way to create the smoothest possible flow of regular preventive

maintenance work, while still leaving enough time to carry out those ³follow-on´ corrective

maintenance tasks that were identified from conducting the preventive/predictive checks

during the last maintenance stop.

It is important to notice that just because two checklists may have the same frequency, it is

not necessary to schedule them to be done at the same time. Sometimes, of course, it does

make practical sense to schedule PMs for the same day, but don¶t assume that this is always

true. As a general rule, in an automated or continuous process production environment, thetotal amount of work on one checklist or work planned for one maintenance period should

not exceed 80 percent of the total time available.

Figure 2 ± Smoothing the PM workload



In order to achieve this smoothed workload pattern, it may be necessary to return to the

timings, frequencies, groupings, start dates, etc., that were specified in the original analysis

and rework some of the data. This is the iterative approach that was mentioned earlier in

the description of Figure 1.

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