Time Estimation In Cpm
Time Estimation in CPM: (cont.): Slack timeSlack time is difference between latest event and the earliest event time i.e. TL i – tE i = τi
a) Float: Now let us define the times for activities i – j.
b) Earliest start time: - This is the earliest occurrence time for the event from which the activity arrow originates and is represented by TEi
c) Earliest finish time:- This is the earliest occurrence time of the event from which the activity arrow originates plus the duration of the activity. TE i tE ij
d) Latest start time: -This is the latest occurrence time for the node at which the activity arrow terminates minus the duration of activity i.e. TLj – tE ij
e) Latest finish time:-This is the latest occurrence time for the node at which the activity arrow terminates, represented by TL j
Maximum time available for activity is TL j – TEi
f) Total float:- If the job i – j requires time tij units, the actual float for jobs i – j is the difference between the maximum time available for the job and the actual time. Total float for i – j = (TL j – tEi ) – tij = (TL j – tij ) – TE i This is the latest time for the activity minus the earliest start time.
g) Free float:- Free float for an activity is based on the possibility that all events occur at their earliest times that means all activities start as early as possible. If you have two activities i – j and j – k i.e., activity j – k is a successor activity to activity i – j
Let TE i = Earliest Occurrence Time for event ‘i’.TE j = Earliest Occurrence Time for event ‘j’.
a) Another type of float is ‘‘Independent Float’’. Consider the activity i–j. Activity h – i is predecessor to i – j and activity j – k is a successor to activity i – j and TL i is to latest finish time of activity h – i.
- And activity j-k starts at the earliest possible moment i.e. TE j. This means activity i – j can
- take time duration between TE i to TEj – TL i , without affecting the networks. The differencebetween the TEj – TL i and tE ijis known as Independent Float. Independent float for i – j = (TE j – TL i ) – tE ij
- Another type of float is Interference Float. Interference Float is the difference between Total Float and the Free Float. In fact it is head event slack. Interference float = Total Float – Free Float
