The C Chart is a control chart of the number of defects. It can be used to track the number of defects and detect signs of special causes.
1. Choose ProcessMA > Control Charts > Attribute Charts > C.
2. In Variable, select the column containing the data.
3. Click OK.
Optional
4. In Mean, enter the population mean, otherwise it will be estimated by the sample mean.
5. In Control limit multiples, enter the position to draw the upper and lower control limits. Multiple entries must be separated by commas (,).
6. In Lower limit bound, enter the bound on the lower control limit.
7. In Upper limit bound, enter the bound on the upper control limit.
8. In Phase, select the column containing the phase codes. (Phase can useful to compare groups of data like before and after improvement)
Note To select a column of data into a textbox, double-click on any of the column names shown in the list on the left of the dialog box while in the textbox.
Variable: Numeric.
Mean: Numeric.
Control limit multiples: Numeric.
Lower limit bound: Numeric.
Upper limit bound: Numeric.
Phase: Text or Numeric; Must contain equal number of data points as the Variable.
You work in a paper manufacturing plant and you need to control the quality of the paper. For each batch, you inspected 100 pieces of paper to make sure that they are not stained. You want to use the C Chart to help you monitor the quality.
1. Open worksheet ProcessMA > Tools > Data Files > Control.xls.
2. Choose ProcessMA > Control Charts > Attribute Charts > C.
3. In Variable, select I – Stained.
4. Click OK.
Interpretation
The process is stable as the data points are randomly distributed and lie within the control limits.