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1. Definition
2. Objectives
3. When to Use
4. Types
5. Methods
6. Benefits
Control charts are vital quality control tools used across manufacturing, healthcare, and service industries. This guide explains what control charts are, their applications, types, and how they improve process performance and reduce defects.
1. What is Control Chart ?
A control chart is used to examine a process to see if it is stable or to maintain the stability of a process.
This method is often used to analyze a process. To do so, a chart is created from data collected for a certain period of time, and dots plotted on the chart are examined to see how they are distributed or if they are within the established control limit.
After some actions are taken to control and standardize various factors, this method is also used to examine if a process is stabilized by these actions, and if so, to keep the process in a stable state.
2. When is it used and what results will be obtained?
There are two types of control charts: one used for managerial purposes and the other for analytical purposes.
A control chart is used to identify dots that are outside the control limit, which indicate some anomalies in a process.
In addition, seven consecutive dots showing values that are below or above the mean (central) value, or an increment or a decline represented by seven consecutive dots also indicate “a problem in a process.”
We need to examine what has caused such a tendency or an increment/decline.
Method
Usage
Used to observe a change caused by elapse of time.
[Used during phases to monitor the situation, analyze causes, review effectiveness of an action, perform standardization, and implement a selected control measure]
Control Chart for Managerial Purposes: Extends the line indicating the control limit used for analytical purposes to plot data obtained daily to keep a process in a good state.
Control Chart for Analytical Purposes: Examines a process if it is in a controlled state by collecting data for a certain period of time. If the process is not controlled, a survey is performed to identify its cause and develop countermeasures.
Result
Can identify a change caused by elapse of time.
Can judge the process if it is in its normal state or there are some anomalies by examining the dots plotted on the chart.
In the example “x bar ” -R control chart, “X bar” represents the central value, while “R” indicates the range.
Frequently Asked Questions About Control Charts
Q: What is the main purpose of control charts?
A: To monitor processes, identify variations, and maintain product quality standards.
Q: What's the difference between control charts and run charts?
A: Control charts include statistical control limits; run charts show trends without limits.
Q: How often should we update control charts?
A: Continuously in manufacturing, or at defined intervals in other processes.
Q: What does it mean when data exceeds control limits?
A: It signals process variation requiring investigation and corrective action.