What are P charts? - Metrology & Quality Control

Q.  Which of the following statements is true?

1. P and nP charts cannot use limit gauges
2. P charts are difficult to understand
3. P charts cannot recognize different degrees of defectiveness in units
- Published on 07 Aug 15

a. Only 1
b. Only 2
c. Only 3
d. All the statements are true

ANSWER: Only 3

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    Discussion

  • Sravanthi   -Posted on 27 Oct 15
    - Attribute charts are used to separate parts into acceptable and unacceptable lots.
    - P and nP charts are control charts for attributes. They can use limit gauges and are easy to understand.
    - P and nP charts cannot recognize different degrees of defectiveness in units.

    P charts:

    1) P charts are used for evaluating fraction defectives when subgroup size is not constant.
    2) Control charts for defectives are used to identify samples which are out of acceptable limits. These charts provide information to the management to initiate corrective actions.

    nP chart:

    1) It is the simplified version of P chart.
    2) This chart is used when number of items in a sample are constant.

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