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Precision of scale weight measurements. The Journal of
Chapter 13, Problem 36E(choose chapter or problem)
Precision of scale weight measurements. The Journal of Quality Technology (July 1998) published an article examining the effects of the precision of measurement on the R-chart. The authors presented data from a British nutrition company that fills containers labeled “500 grams” with a powdered dietary supplement. Once every 15 minutes, five containers are sampled from the filling process, and the fill weight is measured. The table to the right lists the measurements for 25 consecutive samples made with a scale that is accurate to .5 gram, followed by the table below, which gives measurements for the same samples made with a scale that is accurate to only 2.5 grams. Throughout the time period over which the samples were drawn, it is known that the filling process was in statistical control with mean 500 grams and standard deviation 1 gram.
a. Construct an R-chart for the data that is accurate to .5 gram. Is the process under statistical control? Explain.
b. Given your answer to part a, is it appropriate to construct an \(\bar{x}\)-chart for the data? Explain.
c. Construct an R-chart for the data that is accurate to only 2.5 grams. What does it suggest about the stability of the filling process?
d. Based on your answers to parts a and c, discuss the importance of the accuracy of measurement instruments in evaluating the stability of production processes.
Questions & Answers
QUESTION:
Precision of scale weight measurements. The Journal of Quality Technology (July 1998) published an article examining the effects of the precision of measurement on the R-chart. The authors presented data from a British nutrition company that fills containers labeled “500 grams” with a powdered dietary supplement. Once every 15 minutes, five containers are sampled from the filling process, and the fill weight is measured. The table to the right lists the measurements for 25 consecutive samples made with a scale that is accurate to .5 gram, followed by the table below, which gives measurements for the same samples made with a scale that is accurate to only 2.5 grams. Throughout the time period over which the samples were drawn, it is known that the filling process was in statistical control with mean 500 grams and standard deviation 1 gram.
a. Construct an R-chart for the data that is accurate to .5 gram. Is the process under statistical control? Explain.
b. Given your answer to part a, is it appropriate to construct an \(\bar{x}\)-chart for the data? Explain.
c. Construct an R-chart for the data that is accurate to only 2.5 grams. What does it suggest about the stability of the filling process?
d. Based on your answers to parts a and c, discuss the importance of the accuracy of measurement instruments in evaluating the stability of production processes.
ANSWER:
Step 1 of 6
a) We need to construct an R-chart for the given data as shown below
The formulas used in construction of R-chart are as shown below:
Where,
k is the number of samples.
Use MINITAB using the following instruction set as follows:
1) Type or Import data in columns representing weights Wt1, Wt2, Wt3, Wt4, and
Wt5 of fill weights according to 0.5 Grams.
2) Select R bar... from the Variable Charts for Subgroups in Control Charts
of Stat ribbon.
3) Specify Length for “Observations of subgroups are in one row of
columns“.
4) Check all the tests for the special causes in Tests ribbon of R bar Options…
tab, then click estimates and check the R bar.
5) Click Ok.
The MINITAB output is as shown below:
From the above output, we have the following information: