Three types of variation :
1.within a piece
2. piece to piece
3. time to time
variations wrt to process:
Continuous and batch process
Sources of variation :
1. equip.
2. matl.
3. environment
4. operation
Sources of Variation in Production and services process :
Common causes :
Random causes that we cannot identify
Unavoidable
Cause slight difference in process variable like dia, weight, service time, temp. etc.
Assignable causes of variation :
Causes can b identified and eliminated
Typ. causes are poor employee training, worn tool, machines needing repair etc.
Basic principles :
A process that is operating with only Chance causes of variation present is said to be in statistical control.
A process that is operating in the presence of assignable causes is said to be out of control.
The eventual goal of SPC is the elimination of variability.
)_________
Types of control charts :
1 Variable Control charts: This applies to data that follows a continuous distribution
2.Attributes control charts: These charts are applied to data that follow a discrete distribution.
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