Pert Cpm

PERT - CPM By Naveed I. Salman

[email protected], 03215168779

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Quote A dream is just a dream. A goal is a dream with a plan and a deadline. - Harvey Mackay

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Project Management What is a project? A project is a series of activities directed toward the accomplishment of a desired objective.

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Project Management •

Characteristics of Projects – Unique, one-time operations – Involve a large number of activities that must be planned and coordinated – Long time-horizon or critical time constraints – Goals of meeting completion deadlines and budgets • Examples – Building a house – Planning a meeting – Introducing a new product

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Project Scheduling Management

Project scheduling is concerned with the techniques that can be employed to manage the activities that need to be undertaken during the development of a project. Scheduling is carried out in advance of the project commencing and involves: – – – –

identifying the tasks that need to be carried out; estimating how long they will take; allocating resources (mainly personnel); scheduling when the tasks will occur.

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Project Scheduling Management

• Once the project is underway control needs to be exerted to ensure that the plan continues to represent the best prediction of what will occur in the future:

•

–

based on what occurs during the development;

–

often necessitates revision of the plan.

Effective project planning will help to ensure that the systems are delivered:

–

within cost;

– within the time constraint; – to a specific standard of quality.

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Project Management Tools • Older simpler - Gantt Chart • More modern – CPM/PERT • Newest – Microsoft Project ™

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Gantt Chart Start

Activity

5

10

Days After Start 15 20 25 30

5

10

15

35

40

45

50

35

40

45

50

Foundation Framing Plumbing Electrical Wall Board Siding Paint Interior Paint Exterior Fixtures Start

20 25 30 Days After Start

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Advantages of Gantt 1. Easy to understand 2. Easy to construct

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Project Management • PERT - Project Evaluation and Review Technique • CPM - Critical Path Method

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PERT/CPM • PERT –

Program Evaluation and Review Technique – Developed by U.S. Navy for Polaris missile project – Developed to handle uncertain activity times

• CPM – Critical Path Method – Developed by Du Pont & Remington Rand – Developed for industrial projects for which activity times generally were known

• Today’s project management software packages have combined the best features of both approaches. 11

Project Management PERT/CPM • In projects that are non-repetitive information necessary for control is sparse, non-existent or only marginally relevant. • Project control then requires: – A logical methodology showing the required tasks and the interrelationships of these tasks – Estimation of the resources required for each activity/step • • • •

Time Money Personnel Equipment 12

PERT/CPM Type Projects • • • • •

Construction Engineering Software Development Equipment Cut-over Anything with many interdependent activities/steps

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Network Diagram • Activities • Events

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ACTIVITIES • Activities are shown as lines or arrows

• Activities require time and other recourses

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Activities • Some may be executed simultaneously DO THIS AND AT THE SAME TIME DO THAT

• Some cannot be performed until others are completed

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Situations in network diagram B

A

A must finish before either B or C can start C

A

C

both A and B must finish before C can start

B A

C

B A

D B

A must finish before B can start

Dummy C

both A and C must finish before either of B or D can start

D

both A and C must finish before D can start 17

EVENTS

• Events or nodes or mileposts or circles • They consume NO time and show connections between activities • Every PERT/CPM chart has one Start event and one end event 18

CPM -Critical Path Method • A tool to determine duration based on the identification of the Critical Path through the activity network. • Times are known with some high degree of certainty. • Management can determine the duration of a project and concentrate efforts on Critical Path activities. 19

PERT Program Evaluation and Review Technique • Time are NOT known well (uncertainty) • Statistics used to estimate probability of finishing within a given time

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The Six Steps Common to PERT & CPM ♦ ♦

♦ ♦ ♦ ♦

Define the project and identify each activity Develop relationships among the activities. (Decide which activities must precede and which must follow others.) Draw the network connecting all of the activities Assign time and/or cost estimates to each activity Compute the longest time path through the network. This is called the critical path Use the network to help plan, schedule, monitor, and control the project

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Simple CPM Chart

START

END

1 Open Book

Read Chapter

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Calculating times 4 3 2

4

START

END 3

2

4

• Time for top route = 2 + 4 + 4 + 3 = 13 • Time for bottom route = 2 + 3 + 2 + 4 = 11

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Critical Path 4 3 2

4

START

END 3

2

4

• Time for top route = 2 + 4 + 4 + 3 = 13 • Time for bottom route = 2 + 3 + 2 + 4 = 11

• Top is Critical path 24

Slack time No SLACK here

4 3

2

4

START

END 3

2

4

• Time for top route = 2 + 4 + 4 + 3 = 13 • Time for bottom route = 2 + 3 + 2 + 4 = 11 •

For activities not on Critical path

Slack time = 2 25

Slack time 4 3 2

4

START

END 3

B

2

4

• For activities not on critical path the slack time is extra time that could be used if necessary • If event B is reached in 6 days is there a significant problem? • •

No, not if the cause was the activity that should have taken 3 days took 4 Yes, if the cause was the 2 day activity following start took 3 days 26

Review of PERT/CPM • A project network can be constructed to model the precedence / order of the activities and the relationship between activities. • The Lines of the network represent the activities. • The Circles of the network show events. • A critical path for the network is a path consisting of activities with zero slack.

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PERT Activity Times • 3 time estimates – Optimistic times (a) – Most-likely time (m) – Pessimistic time (b)

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• Follow normal distribution • Expected time: t = (a + 4m + b)/6 • Variance of times: v = ((b - a) /6) 2 28

Time Estimation • Estimates of Activity Times Activity time is the elapsed time required for an activity. Estimating activity times is probably one of PERT’s most critical features. • Managers are reluctant to commit themselves to a rigid time schedule. – Weather conditions, alone, prompt uncertainties and make it difficult for the manager to develop a single time estimate. However, experience has shown that managers are less reluctant if allowed three different estimates, especially when they understand PERT and how the concept of three time estimates is used. PERT, therefore, calls for not one, but three estimates of every activity time and allows the manager an opportunity to express his uncertainty about the possible time range of an activity.

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Time Estimation • All three time estimates assume a static level of resource use. The estimates should be as good as possible because PERT results depend directly on them. To obtain accurate estimates is not easy. It will require research, collaboration with planning team members, and homework. • Simple guesswork is inadequate. If some time estimates are mere guesses, the manager will soon realize that they jeopardize or needlessly extend the project schedule date. Once the estimator realizes that his contributions are a small, but vital component of the PERT system, he will try to steadily improve his estimates. In short, guesswork will not replace intelligently derived estimates. 30

Time Estimation • The person most familiar with the operation and requirements of each activity should submit the three time estimates. These should meet the following criteria: – 1) Optimistic Time -- the minimum time period in which the activity can be accomplished, i.e., the time it would take to complete it if everything proceeded better than expected. (labeled a.)

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Time Estimation 2) Most Likely Time -- the best estimate of the time period in which the activity can be accomplished, i.e., the estimate submitted if one (only) had been requested. (labeled m.) 3) Pessimistic Time -- the maximum time period it would take to accomplish the activity, i.e., the time required if everything went wrong, excluding major catastrophes. (labeled b.)

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Time Estimation • It is acceptable to state these estimates in days, weeks, or months as long as the measure is used consistently. Once made, activity time estimates are firm and should not be changed without a change in the nature and scope of the activity or in the level of resources allocated to it. The following time relationships must be adhered to: ... a equal or less than m which is equal or 33 less then b

Some Important Points • The process is no better than the network and the time estimates – People do this – Knowledgeable people must determine which activities must proceed others and the time each activity will require – Some careful estimates are still better than no information

• The resulting schedule should be a normal schedule. – A Crash schedule exists when extra resources are added to reduce time.

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Advantages of PERT/CPM • Especially useful when scheduling and controlling large projects. • Straightforward concept and not mathematically complex. • Graphical networks aid perception of relationships among project activities. • Critical path & slack time analyses help pinpoint activities that need to be closely watched. • Project documentation and graphics point out who is responsible for various activities. • Applicable to a wide variety of projects. • Useful in monitoring schedules and costs. 35

Benefits of CPM/PERT • • • • •

Useful at many stages of project management Mathematically simple Give critical path and slack time Provide project documentation Useful in monitoring costs

CPM/PERT can answer the following important questions: •How long will the entire project take to be completed? What are the risks involved? •Which are the critical activities or tasks in the project which could delay the entire project if they were not completed on time? •Is the project on schedule, behind schedule or ahead of schedule? •If the project has to be finished earlier than planned, what is the best 36 way to do this at the least cost?

Sandwich PERT Chart A. B. C. D.

Toast Bread Make an egg omelet Spread butter on toast Spread omelet on toast

3 minutes

2 minutes

1 minute

1 minute

7 minutes 5 minutes

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Practice Exercise Activities

Pre Activity

Duration in Cost in Weeks (000) Rs

a

-

6

2

b

-

8

3

c

-

5

5

d

b

13

7

e

c

9

11

f

a

15

9

g

a

17

5

h

f

9

8

i

g

6

4

j

d, e

12

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Questions / Answers • ??

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Solution • Critical Path

f, 15 h, 9

g, 17

a, 6

i, 6 b, 8 d, 13

j, 12

c, 5 e, 9 [email protected], 03215168779

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Your Presenter • Naveed I. Salman M. Sc (Mathematics), MCS, MIT, M.A.(EPM) • [email protected] • 0321 5168 779

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The End Thank You

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