Cpm And Pert

CPM and PERT A project is defined as a combination of inter related activities that must be executed in a certain order before the entire task can be completed. The activities are inter related in a logical sequence in the way that some activities cannot start until other are competed. An activity in a project is usually viewed as a job requiring time and recourses for its competition. Project management has evolved as a new field with the development of two analytic techniques for planning scheduling and controlling of projects. These are the critical path method (CPM) and the project evaluation and review technique (PERT). PERT and CPM are basically time anointed methods in the sense that they both lead to determination of a time schedule. Both techniques are usually referred as “Project scheduling” techniques. Project scheduling by PERT-CPM consist of three phases. B Planning C Scheduling D Controlling A. PLANNING: The planning phase is by breaking down the project into distinct Activities. The time extras for the another are then determined and a network (Or arrow) diagram is constructed with each of in ARCS (arrows) representing of the interdependencies between the activities of the project. The construction of the arrow diagram in a planning phase has the advantage of studying the different jobs in details. Perhaps suggesting improvement before the project is actually executed. B. SCHEDULING: The ultimate objective of the scheduling phase is to construct a time Chart showing the start and finish times for each activity as well as its relationship to other activities in the project. In addition, the schedule must pin-point the Critical Activities which require special attention if the project is to be completed on time. For the non-critical activities the schedule must show the amount of slack or float time Which can be used. ACTIVITY: The head of the arrow indicated where task ends and the tail where task ends and the tail where the task begin.

EVENTS: An event represent a point in time that signifies the completion of some Activities and the beginning of new ones. E.g. wall built, foundations dug etc. DUMMY ACTIVITIES: It is an activity which does not consume time or resources. NETWORKS: This is the combination of activities, dummy activities and events. CRITICAL PATH: It gives shortest time in which the whole project can be competed. 1. The construction of a building or a highway. 2. Planning and launching a new project. 3. Installing and debugging a computer system. DIFFERENCES BETWEEN CPM & PERT 1. CPM is activity oriented i.e. CPM network is built on the basis of activities. Also result Of carious calculation are considered in terms of activities of the project. On the other hand, PERT is event oriented. 2. CPM is a deterministic model i.e. it dose not take into account the uncertainties Involved in the estimation of time for execution of a job or an activity. It completely Ignores the probabilistic element of the problem. PERT however is a probabilistic Model. It uses three estimates of the activity time- optimistic, pessimistic and most Likely with a view to take into account time uncertainty. This the expected duration of Each activity is probabilistic indicates that there is fifty percent probability of getting The job done within the time. 3 CPM place dual emphasis on time and cost and evaluate the trade off between project cost and project time. By deploying allows the project manager to manipulate project duration within certain limits so that project duration can be shortened to an optimal cost. On the other hand : PERT is primanly concerned with time. It helps the manager to schedule and coordinate various activities so that the project can be completed on schedule time.

FLOAT: Float is the flexibility available in any activity which can be absorbed either by delaying that activity or by enlarging its duration. There is no difference between float and slack. FLOAT refers to an activity and SLACK refers to an event. 1. TOTAL FLOAT: The total float of an activity represents the amount of time by which activity can be delayed without delaying the project completion date. Total float = LF-EF = LS-ES 2.

FREE FLOAT: Free float is that portion of the total float within an activity can be manipulated without affecting the float of subsequent activities. Free float = Total float – Head slack

3. INDEPENDENCE FLOAT: This is the amount of time an activities are completed as Late as possible and all succeeding activities are completed as late possible and all succeeding activities started as early as possible. Independence float = Free float – Tail slack 4.

INTERFERING FLOAT: Interfering float is that part of the total float which causes a reduction in the float of the successor activities. Interfering float = LF – ES+1 Where +1 indicates succeeding activity