## How do you know if a control chart is out of control?

The tests state that an out of control situation is present if one of the following conditions is true: 1) Seven points in a row above the average, 2) Seven points in a row below the average, 3) Seven points in a row trending up, or 4) Seven points in a row trending down.

### What are the 4 types of control charts?

Types of Control Charts (SPC).

• X bar control chart.
• Range “R” control chart.
• Standard Deviation “S” control chart.
• Attribute Control Charts:
• “u” and “c” control charts.
• “p” and “np” control charts.
• Pre-control Charts.

What does a control chart provide that a run chart doesn t?

A run chart can help you spot upward and downward trends and it can show you a general picture of a process. A control chart also plots a single line of data over time. However, control charts include upper and lower control limit lines with a centerline. Run charts lack the benefit of statistical control limits.

What is a control chart example?

Most examples of a control chart considers two causes of fluctuation, common causes and special causes. We could take baking a cake as an example of a common cause in a control chart. The lack of baking powder is a special cause as it “causes” the cake baking process to fail.

## What is the difference between in control and out of control in the control process?

When points on a control chart move outside the upper or lower control limit, the process is said to be “out of control.” As long as the points are within control limits, the process is “in control.” But, what does an out of control process indicate? Many believe that an out of control process produces defective parts.

### What does a control chart display?

Control charts are used to routinely monitor quality. In general, the chart contains a center line that represents the mean value for the in-control process. Two other horizontal lines, called the upper control limit (UCL) and the lower control limit (LCL), are also shown on the chart.

Which two control charts are typically used together?

An X-bar and R (range) chart is a pair of control charts used with processes that have a subgroup size of two or more. The standard chart for variables data, X-bar and R charts help determine if a process is stable and predictable.

Why are XBAR and R charts used together?

The X-Bar Chart is typically combined with an R-Chart to monitor process variables. If the variable isn’t under control, then control limits might be too general, which means that causes of variation that are affecting the process mean can’t be pinpointed. Each point on the chart acts as a subgroup mean value.

## What are the disadvantages of control charts?

A disadvantage of control charts for variables and attributes is that they only use data from the most recent measurement to draw conclusions about the process. This makes it quite insensitive to shifts on the order of 1.5 standard deviations or less.

### Is control chart and run chart same?

A Control chart is a more advanced version of a Run chart. Whilst this chart still plots a single line of data, it also displays an upper line for the upper control limit and a lower line for the lower control limit.

What should a control plan contain?

Seven attributes to consider when creating a control plan are:

• 1.1 Measurements and Specifications.
• 1.2 Input/Output to a Process.
• 1.3 Processes Involved.
• 1.4 Frequency of Reporting and Sampling Methodology.
• 1.5 Recording of Information.
• 1.6 Corrective Actions.
• 1.7 The Process Owner.
• 1.8 Summary.

Can a process be out of control but capable?

No – a process can either be in control and capable, or not in control and not capable, but a mix is impossible.

## When does a control chart indicate out of control?

A control chart can indicate an out-of-control condition even though no single point plots outside the control limits, if the pattern of the plotted points exhibits non-random or systematic behavior.

### How are control chart rules used in stability analysis?

Control chart rules are used to perform stability analysis An unstable process is not predictable and is considered “out of control”. The concepts of process control and process stability are important because: a process must be stable before you can perform process capability analysis to determine if it meets customer specifications.

When do X bar and your charts get out of control?

If the combined X-bar and R charts exhibit frequent out-of-control signals, the special causes responsible for these signals should be identified and eliminated before proceeding.

Why do you need special causes in a control chart?

Because the action you take to improve your process depends on the type of variation present. If special causes are present, you must find the cause of the problem and then eliminate it from ever coming back, if possible. This is usually the responsibility of the person closest to the process.