A c-chart is used to monitor the number of defects per unit for process output.

Q: What is the c

A c-chart is an attributes control chart used with data collected in subgroups that are the same size. C-charts show how the process, measured by the number of nonconformities per item or group of items, changes over time. Nonconformities are defects or occurrences found in the sampled subgroup.

Q: What chart control the number of defects per unit of output?

The u-chart is a quality control chart used to monitor the total count of defects per unit in different samples of size n; it assumes that units can have more than a single defect. The y-axis shows the number of defects per single unit while the x-axis shows the sample group.

Q: Which chart is used for number of defects?

c chart is also known as the control chart for defects (counting of the number of defects). It is generally used to monitor the number of defects in constant size units.

Q: What is p

A p-chart is used to record the proportion of defective units in a sample. A c-chart is used to record the number of defects in a sample. Consider the following example: A process produces jelly beans. Small spots on a jelly bean are defects.

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Statistical Process Control Full Details
The SPC Control Chart.
Types of control charts

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Variable Control Charts:
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.
Which one of the following control chart is used for the number of defects per unit?
Answer (Detailed Solution Below)
What is the c
What chart control the number of defects per unit of output?
Which chart is used for number of defects?

There are various types of control charts which are broadly similar and have been developed to suit particular characteristics of the quality attribute being analyzed. Two broad categories of chart exist, which are based on if the data being monitored is “variable” or “attribute” in nature.

Variable Control Charts:

X bar control chart.

This type of chart graphs the means (or averages) of a set of samples, plotted in order to monitor the mean of a variable, for example the length of steel rods, the weight of bags of compound, the intensity of laser beams, etc.. In constructing this chart, samples of process outputs are taken at regular intervals, the means of each set of samples are calculated and graphed onto the X bar control chart. This chart can then be utilized to determine the actual process mean, versus a nominal process mean and will demonstrate if the mean output of the process is changing over time.

Range “R” control chart.

This type of chart demonstrates the variability within a process. It is suited to processes where the sample sizes are relatively small, for example <10. Sets of sample data are recorded from a process for the particular quality characteristic being monitored. For each set of date the difference between the smallest and largest readings are recorded. This is the range “R” of the set of data. The ranges are now recorded onto a control chart. The center line is the averages of all the ranges.

Standard Deviation “S” control chart.

The “S” chart can be applied when monitoring variable data. It is suited to situations where there are large numbers of samples being recorded. The “S” relates to the standard deviation within the sample sets and is a better indication of variation within a large set versus the range calculation. An advantage of using the standard deviation is that all data within a set are utilized to determine the variation, rather than just the minimum and maximum values.

Develop your understanding of Control Charts, Process Capability, Process Improvement, etc. …

Attribute Control Charts:

Attribute control charts are utilized when monitoring count data. There are two categories of count data, namely data which arises from “pass/fail” type measurements, and data which arises where a count in the form of 1,2,3,4,…. arises. Depending on which form of data is being recorded, differing forms of control charts should be applied.

“u” and “c” control charts.

The “u” and “c” control charts are applied when monitoring and controlling count data in the form of 1,2,3, …. i.e. specific numbers. An example of such data is the number of defects in a batch of raw material, or the number of defects identified within a finished product.

The c chart is used where there can be a number of defects per sample unit and the number of samples per sampling period remains constant.

In the u chart, again similar to the c chart, the number of defects per sample unit can be recorded, however, with the u chart, the number of samples per sampling period may vary.

“p” and “np” control charts.

P charts are utilized where there is a pass / fail determination on a unit inspected. The p chart will show if the proportion defective within a process changes over the sampling period (the p indicates the portion of successes). In the p chart the sample size can vary over time. A similar chart to the p chart is the np chart. However, with the np chart the sample size needs to stay constant over the sampling period. An advantage of the np chart is that the number non-conforming is recorded onto the control rather than the fraction non conforming. Some process operators are more comfortable plotting the number rather than the fraction of non-conformances.

Pre-control Charts.

Where a process is confirmed as being within statistical control, a pre-control chart can be utilized to check individual measurements against allowable specifications. Pre-control charts are simpler to use than standard control charts, are more visual and provide immediate “call to actions” for process operators. If however a process is not statistically “capable” i.e. having a Cpk of at least 1, pre-control can result in excessive process stoppages.

Develop your understanding of Control Charts, Process Capability, Process Improvement, etc. …

Which one of the following control chart is used for the number of defects per unit?

c - chart
p - chart
Range
Mean

Answer (Detailed Solution Below)

Option 1 : c - chart

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20 Questions 20 Marks 20 Mins

Explanation:

Control Charts:

Control charts are also called a Shewhart chart, a statistical process control chart, or an SPC chart. It is one of several graphical tools typically used in quality control analysis to understand how a process changes over time.
A visual time-series graph that illustrates data points collected at specific time intervals.
Two types of process data:
- Variables: It is continuous data, things we can measure. example includes length, weight, time, temperature, etc
- Attribute: it is discrete data that we count. the example includes a number or percent defective items in a lot, number of defects per item, etc
Types of control charts:
- Variable Charts: These are meant for the variable types of data. X bar and R Chart, X bar and sigma chart for the individual units.
- Attribute Charts: These are meant to type of data p chart, np chart, C chart, U chart.

C Chart:

It is also known as the control chart for defects (counting the number of defects). It is generally used to monitor the number of defects in constant size units.
There may be a single type of defect or several different types, but the c-chart tracks the total number of defects in each unit.

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What is the c

A c-chart is an attributes control chart used with data collected in subgroups that are the same size. C-charts show how the process, measured by the number of nonconformities per item or group of items, changes over time. Nonconformities are defects or occurrences found in the sampled subgroup.

What chart control the number of defects per unit of output?

The u-chart is a quality control chart used to monitor the total count of defects per unit in different samples of size n; it assumes that units can have more than a single defect. The y-axis shows the number of defects per single unit while the x-axis shows the sample group.

Which chart is used for number of defects?

c chart is also known as the control chart for defects (counting of the number of defects). It is generally used to monitor the number of defects in constant size units.

What is p

A p-chart is used to record the proportion of defective units in a sample. A c-chart is used to record the number of defects in a sample. Consider the following example: A process produces jelly beans. Small spots on a jelly bean are defects.