Exam 21: Statistical Process Control

To determine whether the proportion of defectives is in line with specifications,we use a(n):

The $\bar { x }$ chart is employed to determine whether the process distribution means have changed.To determine whether the process distribution standard deviation has changed,we use the S (which stands for standard deviation)chart.

A control chart used to monitor a process whose results are categorized as either defective or nondefective is called a(n)____________________.

In order to test if a production process is under control,30 samples of 1,000 units were drawn and the number of defectives in each sample was determined.The mean sample proportion was found to be .0615.Compute the centerline and control limits for the p chart.

If the average run length of a process is 385,then the $\bar { x }$ control chart will wrongly conclude that the process is out of control once every 385 samples on average.

What is the average run length (ARL)until an $\bar { x }$ control chart signals a false alarm if the control limits are set at $\pm$ 3 standard errors from the centerline?

Samples Production Thirty samples of size 4 were drawn from a production process.The data are shown below. -{30 Samples Production Narrative} Looking at the $\bar { x }$ and S charts developed in a previous question,can you infer that the process is under control? If so,explain why.If not,explain what the problems are.

If your control chart found a series of points all lying within 3 standard errors above the center line,and none lying below the centerline,this could be an indication of assignable variation due to a(n)____________________.

Chance variation in general cannot be eliminated without changing the process.

Assembly Line Random samples of 200 parts were taken on an assembly line every hour for the past 25 hours.The number of defective parts is shown in the accompanying table. Sample 1 2 3 4 5 6 7 8 9 10 11 12 13 Number af Defectives 5 2 4 10 2 6 8 2 0 5 12 11 Sample 14 15 16 17 18 19 20 21 22 23 24 25 Number of Defective5 10 5 13 7 5 7 11 3 16 3 2 10 -{Assembly Line Narrative} Apply the pattern tests to determine if the production process is under control.

What is the average run length (ARL)until an $\bar { x }$ control chart signals a false alarm if the control limits are set at $\pm$ 2 standard errors from the centerline?

Describe what a Type I error is,and what its impact is,in terms of a production process.

A malfunctioning valve in a filling machine can create assignable variation.

The mean of the sample means and the pooled standard deviation of 25 samples of size 4 taken from a production process under control are found to be 150 and 10,respectively.The centerline for the $\bar { x }$ chart is:

We construct a p chart to track the proportion of ____________________ units in a series of samples.

The key to quality is to detect when the process goes out of control.The ____________________ chart is the statistical method that we use to detect problems.

Discuss what we mean by assignable variation in a process and give an example.

If your control chart found a series of points all lying within 3 standard errors above the center line,and none lying below the centerline,this could be an indication of assignable variation due to a(n)____________________.

Statistical process control allows us to detect ____________________ variation only.

Assume that the control limits of an $\bar { x }$ chart are defined as 3 standard errors above and below the centerline.Calculate the probability that a sample mean falls outside the control limits when the process is in fact under control.