KELAPPAJI COLLEGE OF AGRICULTURAL ENGINEERING AND TECHNOLOGY, TAVANUR, KERALA,INDIA

1. CONTROL CHARTS
NAMITHA M R
2011-02-028
B.TECH AGRL. S7
KCAET, TAVANUR

2. Definition
A graphical representation of collected information
A statistical quality control tool used in monitoring
the variations in the characteristics of a product or
service
One of the Seven Basic Tools of Quality

3. Also known as Shewhart charts or Process
behavior charts
First described by Walter A. Shewhart
Purpose- To determine if a manufacturing or
business process is in a state of statistical control
Used to study how a process changes over time

4. Consists of...
A central line for the average
An upper line for the upper control limit (UPC)
A lower line for the lower control limit (LPC)

5. Comparison of current data to these lines provides
details about whether the process variation is:-
Consistent (in control)
or
Unpredictable (out of control)

6. How to draw?
Points representing a statistic or data is taken from
the process at different times
The mean of this statistic using all the samples is
calculated
A centre line is drawn at the value of the mean of
the statistic

7. Standard error of the statistic is calculated using
all the samples
Upper and lower control limits are drawn typically
at 3 standard errors from the centre line

8. If all data points are within the control limits, the
process is said to be ‘in control‘
If data points fall outside the control limits, the
process is said to be out of control

9. Control chart

11. Control Chart: Out-of-Control Signals

13. Advantages...
Determines whether the process is in control or not
Monitor process variation over time
Detects unusual variations taking place in a time

14. Differentiate between special cause and common
cause variation
Assess effectiveness of change
Communicate process performance
Ensures product quality level

15. Disadvantages
False alarms
Flawed assumptions
Special training
Misplaced control limits

16. Conclusion
An understanding of statistical quality control and
variation is essential for an effective assessment
process
Statistical tools like control charts are especially
helpful in comparing performance with historical
patterns and assessing variation and stability