Control charts are a statistical quality control tool used to monitor variations in product or service characteristics over time. They graphically display data collected from a process, with lines indicating the average and upper and lower control limits. If data points fall outside the control limits, the process is considered out of control. Control charts help determine if a process is consistent or unpredictable, detect unusual variations, and assess the effectiveness of process changes.

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