Control Chart
Principles in Quality
Management
If you want to improve your organization's processes, control charts are a
valuable tool. Learn about control chart principles and how they can help you
achieve success.
The Purpose of Control Charts
Reduce Variation
Improve Decision-Making
Control charts help reduce
Control charts provide data that
variation in a process, which
can help you make informed
leads to higher quality outputs
decisions about process
and reduced costs.
improvements.
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2
3
Monitor Performance
Identify Potential Problems
Control charts monitor a
Control charts allow you to
process's performance over time
identify potential problems early
and can help determine if it's
on in the process, before they
stable or unstable.
become major issues.
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Types of Control Charts
X-Bar and R Charts
X-Bar and S Charts
Used for continuous data with subgroup
Used for continuous data with subgroup
sizes of 2 to 9.
sizes > 10.
P Charts
C Charts
Used for discrete data to monitor the
Used for discrete data to monitor the
proportion of nonconforming units in a
number of nonconforming units in a sample.
sample.
Calculating Upper and Lower Control
Limits
Formula for X-Bar
Control Limits
Formula for R Control
Limits
Formula for S Control
Limits
The upper control limit is X-
The upper control limit is R-
The upper control limit is S-
Bar + 3σ and the lower control
Bar*D4 and the lower control
Bar*C4 and the lower control
limit is X-Bar - 3σ.
limit is R-Bar*D3.
limit is S-Bar*C3.
Interpreting Control Chart Results
1
Out of Control Points
If a data point falls outside of the
Common and Special Causes
2
control limits or if there is a pattern
forming, the process may be out of
control.
Control charts distinguish between
common causes of variation, which
are expected, and special causes of
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Actionable Insights
variation, which are unexpected.
Control charts can provide actionable
insights that can help you identify and
eliminate problems with your process.
Common Causes of Variation
1
Tools and Equipment 2
Human Error
Improper use of tools
People are fallible and
Raw materials and
and equipment is the
can make mistakes that
consumables that go
most common cause of
lead to variation.
into a process can vary
variation in a process.
3
Materials
in quality, leading to
variation in output.
Special Causes of Variation
New Process or EquipmentExternal Factors
Mistakes
When implementing a new
External factors, like supplier
Special causes of variation
process or equipment there
changes or natural disasters,
can be the result of a mistake
may be variations until it
can cause special causes of
in the process, such as a
stabilizes.
variation.
calibration error or an incorrect
setup.
Implementing Control Charts
Step 1:
Choose the
Right Chart
Step 2:
Collect Data
Step 4: Plot
the Data
the chosen process
Step 3:
Calculate
Control
Limits
Depending on the
Calculate the
data on the control
type of process and
over an extended
control limits and
chart, making sure
the data being
period of time at a
add them to the
to label the points
monitored, choose
regular interval,
chart.
and axis.
the appropriate
depending on the
control chart before
chart selected.
collecting data.
Collect data from
Plot the collected