CHAPTER 6
Control Charts
OBJECTIVES
• Apply principles of Quality Control to a heat transfer system.
• Collect data on the heat exchanger system.
• Develop a check-list to collect data.
• Create a control chart.
• Describe patterns of instability in a SPC process.
• Apply principles of Quality Control to a distillation system.
• Collect data on the overhead system.
• Develop a check-list to collect data.
• Create a x-bar and r-bar control chart
• Describe process variation.
• Describe how to collect data for a control chart.
• Explain the purpose of a control chart.
• Describe an X-bar chart
• Describe a Range-chart
• Describe Process Capability
• Describe the term “Process in Control.”
• Describe the term “Process out of Control.”
• Construct a control chart
• Define key terms associated with control charts.
REVIEW QUESTIONS
1. Describe natural variability in a process.
Over the years, operations personnel have discovered that there are natural
variations that occur on each equipment system. These variations have not
2. What are the basic elements of a control chart?
3. What is an “assignable cause?”
4. What is the primary purpose of a control chart?
5. What is a control chart and why do we want to use them?
Control Chart—a simple tool designed to quantitatively monitor important
characteristics of a process. It is a picture that allows us to see what changes
have occurred over a period of time, and to study the impact of various factors in
the process that change. When properly used, it prevents us from reacting when
we do not need to react and it will allow us to react when we need to react.
Control charts are designed to:
• achieve higher effective capacity
• identify appropriate adjustments
• Distinguish special from common causes of variation
6. List seven benefits of using a control chart.
• Product more uniform- less variation and fewer rejections
7. What is a subgroup?
8. Describe the term “process in control.”
In any process that is operating within design specifications a natural pattern of
variation exist. Identical processes will have unique characteristics that when
carefully studied will still show signs of natural variation. This natural pattern of
9. Describe the term “process out of control.”
When a process is out-of-control it is typically due to a change in the
process that is responding to an undesirable cause. These undesirable
10. Draw and describe the four patterns of instability listed in this chapter.
11. How do control charts provide a window into the process?
12. Describe how to set up a scatter plot diagram.
The steps in setting up a scatter diagram includes; collecting data in
13. List the four equations used to develop x-bar and r-bar charts.
X chart
15. What role does data collection play in the quality system.
There are three steps in developing a quality system on a process unit; collect
16. Describe histograms or frequency plots.
Histograms or frequency plots is a graphical tool used to understand
variability. The chart is constructed with a block of data separated into five
17. Describe the purpose of SPC in a distillation system.
18. Describe the variables controlled in a distillation process.
19. Describe the four basic systems found in a distillation system.
20. Write the SPC equations used to develop an x-bar chart. Answer:
21. Write the equations used to calculate range. Answer:
Range chart
NAME:____________________________ TEST A
DATE:____________________________
CHAPTER SIX
TEST CONTROL CHARTS
1. Assignable cause is best described as:
a. a simple tool designed to quantitatively monitor important characteristics
of a process.
b. the mean or arithmetic average.
c. a cause of unpredictable variation that can be identified using structured
techniques.
d. a process characteristic that can be checked or counted.
2. An attribute is best described as:
a. a cause of unpredictable variation that can be identified using structured
techniques.
b. a process characteristic that can be checked or counted.
c. the highest point established as the top specification on a control chart.
UCL X-bar = Average X-bar + (A2 X Average R).
d. are boundaries that tell you if the process is in control.
3. The average of a group of process variables is best described as:
a. the difference between the highest and lowest number.
b. the desired value ; also called the nominal value.
c. most frequent measure in a distribution, or the value that occurs with the
greatest frequency in the data.
d. the mean or arithmetic average.
4. A control chart is best described as:
a. a simple tool designed to quantitatively monitor important characteristics
of a process.
b. the spread of the process which is equal to six standard deviations when
the process is in a state of statistical control.
c. a picture that allows us to see what changes have occurred over a period
of time, and to study the impact of various factors in the process that
change.
d. A & C
5. The upper control limit UCL is defined as:
a. the lowest point established as the bottom specification on a control chart.
LCL X-bar = Average X-bar – (A2 X Average R).
b. a term used on a Table designed to identify factors for Range control
limits.
c. are boundaries that tell you if the process is in control.
d. the highest point established as the top specification on a control chart.
UCL X-bar = Average X-bar + (A2 X Average R).
6. X-double bar is best described as:
a. An unbiased smaller sample of a larger population used to represent the
entire population.
b. the average of a series of numbers.
c. the average of the subgroup averages.
d. the average of the subgroup averages.
7. A subgroup is best defined as:
a. the average of a series of numbers.
b. the number of samples that are averaged together to obtain a single data
point.
c. the desired value ; also called the nominal value.
d. An unbiased smaller sample of a larger population used to represent the
entire population.
8. X-bar is defined as:
a. An unbiased smaller sample of a larger population used to represent the
entire population.
b. the average of a series of numbers.
c. the average of the subgroup averages.
d. a simple tool designed to quantitatively monitor important characteristics
of a process.
9. The lower control limit LCL is best described as:
a. the highest point established as the top specification on a control chart.
UCL X-bar = Average X-bar + (A2 X Average R).
b. the desired value ; also called the nominal value.
c. the lowest point established as the bottom specification on a control chart.
LCL X-bar = Average X-bar – (A2 X Average R).
d. the number of samples that are averaged together to obtain a single data
point.
10. The range is best defined as:
a. the difference between the highest and lowest number.
b. most frequent measure in a distribution, or the value that occurs with the
greatest frequency in the data.
c. the desired value ; also called the nominal value.
d. An unbiased smaller sample of a larger population used to represent the
entire population.
11. Control limits are best described as:
a. the highest point established as the top specification on a control chart.
UCL X-bar = Average X-bar + (A2 X Average R).
b. boundaries that tell you if the process is in control.
c. a cause of variation or special cause.
d. the lowest point established as the bottom specification on a control chart.
LCL X-bar = Average X-bar – (A2 X Average R).
12. Process capability is best described as:
a. the desired value ; also called the nominal value.
b. a term used on a Table designed to identify factors for Range control
limits.
c. a term used on a Table to identify the factors established for X-bar control
limits.
d. the spread of the process which is equal to six standard deviations when
the process is in a state of statistical control.
13. The mean is described as:
a. the average of a population.
b. a cause of variation that is small in magnitude and difficult to identify; also
called random or common cause.
c. the middle number in an ordered distribution, or the value that divides a
series of ordered observations so that an equal distribution of numbers
exists above and below.
d. most frequent measure in a distribution, or the value that occurs with the
greatest frequency in the data.
14. The median is best described as:
a. the average of a population.
b. a cause of variation that is small in magnitude and difficult to identify; also
called random or common cause.
c. the middle number in an ordered distribution, or the value that divides a
series of ordered observations so that an equal distribution of numbers
exists above and below.
d. most frequent measure in a distribution, or the value that occurs with the
greatest frequency in the data.
15. The mode is best described as:
a. the average of a population.
b. a cause of variation that is small in magnitude and difficult to identify; also
called random or common cause.
c. the middle number in an ordered distribution, or the value that divides a
series of ordered observations so that an equal distribution of numbers
exists above and below.
d. most frequent measure in a distribution, or the value that occurs with the
greatest frequency in the data.
16. Assignable cause is best described as:
a. the frequency or arrangement of data that may show repetition of
numerical values.
b. a cause of variation or special cause.
c. a quality characteristic that varies or conforms to desired specifications.
d. a cause of variation that is small in magnitude and difficult to identify; also
called random or common cause.
17. Chance cause is defined as:
a. the frequency or arrangement of data that may show repetition of
numerical values.
b. a cause of variation or special cause.
c. a quality characteristic that varies or conforms to desired specifications.
d. a cause of variation that is small in magnitude and difficult to identify; also
called random or common cause.
18. The frequency distribution is:
a. the mode
b. the mean or average
c. the frequency or arrangement of data that may show repetition of
numerical values.
d. the median
19. The target is best described as:
a. the mean
b. the desired value ; also called the nominal value.
c. the mode
d. a quality characteristic that varies or conforms to desired specifications.
20. The sample can be described as:
a. An unbiased smaller sample of a larger population used to represent the
entire population.
b. a liquid or a solid
c. the required mean
d. a quality characteristic that varies or conforms to desired specifications
Answer Key CHAPTER 6 TEST A
CONTROL CHARTS
Answer Key CHAPTER 6 TEST A
INTRODUCTION TO PROCESS ROUBLESHOOTING
