Carillon Technologies Limited

Steps for Constructing an Average and Range Control Chart (no standards given)

 

Step #1.

Collect the data using rational subgroups

(typically more than 100 measurements)

Example:Corn Flake Diameter 

 

Step #2.

Record the data on a data sheet (chart)

(use coded data: d = 29 mm = 20 +9 mm)

  

 

Step #3.

Find the average value and the range for each subgroup.

a) Average =
Sample data #1 =  
 
b) Range =  
Sample data #1 =  
   

 

The completed calculated data set:

  

 

Step #4.

Find the overall average and the average range.

k = number of subgroups

a) Overall average of the averages =

  

Sample Data Overall average =

Uncoded = 6.9 + 20 = 26.9 mm
   
b) Overall range =
Sample Data Overall range =  

 

Step # 5 a.

Calculating the control limits for the Average Chart
   
Sample: Average Control Chart  
 

 

Step#5b. 

Calculating the control limits for the Range Chart

 

   
Sample: Range Control Chart  
 
 Factors Chart  

Factor/Sample Size

 

 

 2

 1.880

 3.268

 0

 1.128

 3

 1.023

 2.574

 0

 1.693

 4

 0.729

 2.282

 0

 2.059

 5

 0.577

 2.114

 0

 2.326

 6

 0.483

 2.004

 0

 2.534

 

Step #6.

Construct the control chart by plotting the average and range points for each subgroup and placing the control limits on the chart

 Average Chart

 

 Range Chart

Step #7.

Perform an analysis to determine if any special causes are acting on the data.

Point out of Control Limits, Shifts, Trends, Cycles

Step #8.

Take corrective action to bring the process into statistical control Using the tools of system alignment followed by system improvement.

Back to Control Charts