PERT/CPM
PROJECT SCHEDULING
• Allocation of resources.
• Includes assigning the starting and completion
dates to each part (or activity) in such a
manner that the whole work (or project)
proceeds in a logical sequence and in an
orderly and systematic manner.
OBJECTIVES OF SCHEDULING
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•
•
•
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To minimize cost of production and storage.
To maintain minimum cash outflow.
Maximum/effective utilization of resources.
Maximum plant utilization.
To ensure maximum customer satisfaction.
PERT
• Program Evaluation and review technique
• Time-event network analysis in which the
various events in a program or project are
identified, with a planned time established for
each.
• These events are placed in a network showing
the relationships of each event to the other
events.
102
9
2
17
56
4
17
8
10
12
36
1
3
10
40
7
8
10
13
9
12
41
10
6
11
19
52
5
12
PERT
• Each circle represents an event.
• Circles are numbered in the order in which the
events occur.
• Each arrow represents an activity- the time
consuming element of a program.
• Activity time represented by the number
between the arrows, is the time required to
accomplish an event.
PERT
• In this example, only a single time is shown for each
activity, but in the original PERT program there were three
“time estimates”.
• Optimistic time: an estimate of the time required if
everything goes extremely well.
• Most likely time: an estimate based on the time the project
engineer really believes is necessary for the job
• Pessimistic time: a time based on the assumption that
some logically conceivable bad luck, other than a major
disaster, will be encountered.
• These estimates are often included in PERT because it is
very difficult, in many engineering and development
projects to estimate time accurately.
ADVANTAGES OF PERT
• Forces managers to plan because it is impossible
to make a time-event analysis without planning
and seeing how the pieces fit together.
• Forces planning all the way down the line
because each subordinate manager must plan the
event for which he or she is responsible.
• Concentrates attention on critical elements that
may need correction.
• Enables managers to prepare reports.
LIMITATIONS OF PERT
• Emphasis on time not costs.
• Not useful when estimates of time cannot be
made.
9
2
4
1
3
8
7
6
5
10
13
11
12
CRITICAL PATH METHOD
• Sequence of events that take the longest time
and that has zero(or the least ) slack time.
• Critical path comprises events 1-3-4-8-9-13.
• Over this path, the activity time for this
sequence of events is 131.6 weeks.
• If promised delivery is in 135 weeks, even this
critical path will have been completed 3.4
weeks ahead of time.
CRITICAL PATH METHOD
• Some of the other paths like 1-2-9-13 are
almost as long as the critical path = 129 weeks
• It is customary to identify several critical paths
in order of importance.
• Identifying the CP makes possible close
monitoring of this particular sequence of
events to ensure that the whole program is on
schedule.