P Chart Design

The C chart displays the number of defects The U chart displays the number of defects per unit The NP chart displays the number of defectives For P charts, the subgroup size may vary but they should each be gt50. Below is a sample set of data which will help illustrate the creation of the P-chart, its centerline and control limits.

Steps in Constructing a p-Chart. Determine the size of the subgroups needed. The size, ni, has to be sufficiently large to have defects present in the subgroup most of the time. If we have some idea as to what the historical rate of nonconformance, p, is we can use the following formula to estimate the subgroup size n3p

The P chart The P chart is the same chart with the nonconformity rate re-expressed as a proportion. So writing l i i D p n , has mean npn p and standard deviation p1 p n . For n200 and p0.03, the center line is 0.03 and the control limits are at 0.03 30.0001455 0.03 0.0362, which gives no LCL and a UCL of 0.0662.

If you would like to download the p chart excel template with the same calculation then, download it from the above given link and similarly you can download the other template or format by Click Here. Interpretation of P Chart In the above p chart, we have seen that one proportion defect value is beyond the upper control limit.

In statistical quality control, the p-chart is a type of control chart used to monitor the proportion of nonconforming units in a sample, where the sample proportion nonconforming is defined as the ratio of the number of nonconforming units to the sample size, n. 1The p-chart only accommodates quotpassquotquotfailquot-type inspection as determined by one or more go-no go gauges or tests, effectively

P charts look at attribute data where the unit is either conforming or nonconforming. P Chart vs. U Charts. U charts are used when the number of nonconformities per unit can be more than one. For example, tracking scratches or dents on a product. P charts only consider whether the unit is conforming or not passfail. P Chart vs. X-bar and R

The NP chart is very similar to the p-chart. However, an NP chart plots the number of items while the p-chart plots proportions of items. Uses. P-charts are used to Detect sudden changes in systems, which can be attributed to a cause. Assess the need for stratification into subgroups, like location, employee, or time of day.

When to use an alternate control chart. If you can count the number of defects on each item, use U Chart, Laney U' Chart, or C Chart to plot the number of defects per unit. If your data exhibit overdispersion or underdispersion, Laney P' Chart may more accurately distinguish between common-cause variation and special-cause variation. Overdispersion can cause a traditional P chart to show an

The P Chart above illustrates the proportion of defective units over a 5-week period. The blue line represents the proportion defective each week. The red dashed line indicates the Upper Control Limit UCLp, and the green dashed line represents the Lower Control Limit LCLp. The shaded area between the UCLp and LCLp shows the expected range

What is a p Chart? Attribute charts p chart is also known as the control chart for proportions. It is used to analyze the proportions of non-conforming or defective items in a process. It uses a Binomial Distribution to measure the proportion of defective or non-conforming units in a sample.. In the p-chart, proportions are plotted on the y-axis, and the number of samples is on the x-axis.