Computations for Control Charts
#31 Practice calculating control limits

1. If = 90.60, = 0.95, and the sample size is 3, determine the control limits for averages and for ranges. Use the control chart formulas on the previous page.
= ______________ = ______________
= ______________ = ______________

2. A filling process has the grand average 10.3 kg, the average range 1.6 kg, and
sample size n = 5. Calculate the upper and lower control limits for and R.
= ______________ = ______________
= ______________ = ______________

#32 Use the spreadsheet data below to answer the following questions:

1. What is the number of observations (individual x's)?

2. What is the subgroup size or the number of observations per sample (n)?

3. How many samples in all were taken ?

4. How much is ? What is the value of ?

5. What is a problem with putting day shift data together consecutively?

6. What other features of the data do you see?

Booth #2 Glue Weight Data, grams-- Day Shift
Day Time Obs.1 (left) Obs.2 (ctr.) Obs.3 (rt.) Average Range
1/2 10:00 31 33 29 31.0 4
11:15 28 28 27 27.7 1
1:30 28 28 27 27.7 1
3:00 26 29 27 27.3 3
3:45 30 35 31 32.0 5
1/3 8:30 26 29 27 27.3 3
10:30 26 28 27 27.0 2
1:30 29 28 27 28.0 2
3:30 26 27 26 26.3 1
1/4 8:30 27 27 26 26.7 1
11:20 27 28 26 27.0 2
1:00 27 28 27 27.3 1
3:45 no data
1/5 9:00 26 28 29 27.7 3
11:00 27 29 26 27.3 3
2:00 27 28 26 27.0 2
3:30 25 29 25 26.3 4
1/6 8:30 27 29 27 27.7 2
11:00 27 29 27 27.7 2
1:45 27 28 28 27.7 1
3:45 28 34 39 30.3 6
1/7 8:30 27 29 26 27.3 3
11:00 27 29 26 27.3 3
2:00 27 29 26 27.3 3
3:45 29 30 28 29.0 2
mean 27.29 29.13 27.08 27.8 2.5
st. dev. 1.34 1.99 1.32 grand ave. ave. range
range 6 8 6    
count 24 24 24 72  
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