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Quality Engineering Report II
p-Chart, np-Chart, and c-Chart
The first section will focus on the p-chart and the np-chart for 25 subgroups of 300 samples that are inspected (n) and the number of nonconforming (np) samples are recorded.Â
The second section will focus on the c-chart for the number of non-conformities (c) on a sample.
Quality Engineering Report II: Text
p-Chart and np-Chart
The data to the left shows 25 subgroups each consisting of 300 inspected samples (n) and the number of nonconforming samples (np) in each sub group. The proportion nonconforming (p) can be calculated by dividing the number nonconforming by the total sample size. The average of the number nonconforming (np) is 5.56 and the average of the proportion nonconforming (Pbar) is 0.0185.
This chart shows the proportion nonconforming (blue line) to the average of the proportion nonconforming (orange line) and its upper control limit of 0.042 (gray line). Normally the lower control limit would be on this chart as well but it was calculated to be -0.005 and since it is not possible to have a negative amount of nonconforming product it has been excluded, thus the lower limit can be considered 0. This chart plots the fraction defective in the subgroup size and can be used for a constant or a varying subgroup size. The chart is based on a normal distribution approximation to the binomial distribution.
This chart shows the number nonconforming (blue line) to the average of the number nonconforming (orange line) and its upper control limit of 12.634 (gray line). Normally the lower control limit would be on this chart as well but it was calculated to be -1.514 and since it is not possible to have a negative amount of nonconforming product it has been excluded, thus the lower limit can be considered 0. This chart plots the number defective in a subgroup size of constant. The chart is based on a normal approximation to the binomial distribution.
Quality Engineering Report II: Services
c-Chart
The data to the left shows 30 samples and the number of nonconformities found on each sample (c). This chart is meant to count the number of deformities on a part rather than how many parts are defective in a group. It is used when a fixed subgroup or sample size is used and all parts inspected are the same size. There is no consideration as to what each defect on the part is.
This chart shows the number of nonconformities on a part (blue line) to the average number of nonconformities (orange line) and its upper control limit of 16.434 (gray line). Normally the lower control limit would be on this chart as well but it was calculated to be -0.501 and since it is not possible to have a negative amount of nonconformities on a piece it has been excluded, thus the lower limit can be considered 0. This chart plots the number of deformities per part.
Quality Engineering Report II: Services
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