PERT and CPM

In mechanical engineering, CPM stands for Critical Path Method. It was first used by Morgan R. Walker in 1957. The practical use of this concept is to make detailed and planned time schedules. It encourages discipline and provides a standard method for communicating projects. It is very effective in production management and industrial engineering. The term “PERT” stands for “program evaluation and review technique.”

PERT and CPM

The main applications of PERT and CPM are

• Research and development projects 
• Equipment maintenance 
• Construction (large buildings, bridges, dams, etc.)
• Establishing new industries 
• Planning and launching modern products 
• Designing plants, machines, and systems

The organisation of big programs 

Activity: the part of a project that consumes most of the time and resources and generally involves physical and mental labour. 

Event: It depicts a moment when either the project begins or ends but doesn’t include any resources or labour. 

Dummy activity: it is an activity that shows the relationship of one activity with another but doesn’t include any resources or time. It is depicted by arrows in the dotted line. 

Dangling: It is a condition when any other activity, apart from the finale activity, doesn’t have a successor. 

PERT-PERT is an event-oriented 

A PERT is a probabilistic model. It indicates that it considers uncertainties while estimating the time of a job or an activity. 

PERT uses 3 estimations of time, which are 1) optimistic time, 2) pessimistic time, and 3) most likely time.

Optimistic time: it denotes the minimum time to complete a task if everything goes accordingly. 

Pessimistic time: denotes the maximum time required for the completion of activity if everything goes accordingly. 

Most likely time: This denotes the time required for completing an activity under normal working conditions. 

The main applications of PERT are planning and making schedules. It helps the management to coordinate and plan various activities so that the project can be completed on schedule.

PERT is commonly used for those projects which are not repetitive. For example, projects related to research and development will be PERT is applicable for those projects which require an ample amount of time to execute. 

The process of PERT analysis requires the following steps:

• Identifying the activities of a project
• calculating the completion date
• defining relationships between one activity and the other.
• Drawing the network
• Using the network to obtain the scheduled data activity

As mentioned earlier, PERT is majorly used for scheduling different tasks and also to coordinate those tasks to execute a project. 

It plays a major role in providing the blueprint for the project and is efficient in project evaluation.

Formula

The expected time of completion is given by this formula.

When the expected time of completion is E, and

O = optimistic time estimate

M = most likely time estimate

P = pessimistic time estimate 

Pert Estimate E = (O + 4M +P) / 6

CPM (critical path method)

CPM is a method that is used for tasks whose time of completion is already known. 

It is mainly used to determine the expected time of completion of a project. 

A project and all of its components are graphically represented, and this representation is called a network. A network path consists of several points that denote the end and beginning of the project. The longest path through this network is called the critical path. The critical path determines the minimum duration at which the project can be completed. Activity in the network is considered critical if a delay in the starting point also results in a delay in the completion. But in this case, the activity time is known for certain. 

So, it can be concluded that the critical path is the longest in the network that determines the shortest duration to complete the project. 

So, it can be concluded that PERT is event-oriented and CPM is activity-oriented. PERT is associated with probabilistic activity, and CPM is associated with a deterministic activity. PERT is based upon a three-time estimation of the completion of a project, but CPM is based upon a single estimate of the completion of a project. PERT usually doesn’t consider cost analysis, but CPM does emphasize cost analysis and crashing is done to minimise the cost of the project.

Conclusion

PERT and CPM are two concepts in engineering that are mostly related to time management and scheduling projects. These two concepts are important for GATE exam aspirants.