The P Chart is a control chart used to track the number of defectives and detect signs of special causes. The NP chart is normally used when the subgroup size is constant. The data is assumed to follow a Binomial distribution.
At the Excel Menu (For Excel 2007, go to Add-ins first)
Choose ProcessMA > Control Charts > Attributes Charts > NP
In Variable, select the column containing the data (Positive integer)
In Subgroup Sizes , select the column containing subgroup sizes (Optional, Positive integer, >=Variable)
In Constant Subgroup Size , enter the subgroup size if it is constant (Positive integer, >=Variable)
In Proportion, enter the population proportion, otherwise it will be estimated from the sample (Optional, Numeric, >0 & <1)
In Control Limit Multiples, enter the position to draw the upper and lower control limits. Multiple entries must be separated by commas (Optional, Numeric, >0, Up to 3 multiples)
In Lower Limit Bound, enter the bound on the lower control limit (Optional, Numeric)
In Upper Limit Bound, enter the bound on the upper control limit (Optional, Numeric)
In Phase, select the column containing the phase indicators (Optional, >=2 distinct values)
Check the various checkboxes to perform respective tests
Click OK
You work in a paper manufacturing plant and you need the control the quality of the paper. For each batch, you inspect a certain quantity to make sure that the papers are ‘white enough’ for quality control. You want to use the NP chart to help you monitor.
Open data worksheet by choosing ProcessMA > Tools > Data
Choose ProcessMA > Control Charts > Attributes Charts > NP
In Variable, select S - Stained
In Subgroup Sizes , select T - Sampled
Click OK
Sample 20 is outside the control limit and you may want to investigate that production batch for quality issues.
Copyright © ProcessMA