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# What does attribute charts used for? Mention different types of attribute control charts and explain each type

Attribute Control Charts are a set of control charts specifically designed for tracking defects (also called non-conformities). These types of defects are binary in nature (yes/no), where a part has one or more defects, or it doesn’t. Examples of defects are paint scratches, discolorations, breaks in the weave of a textile, dents, cuts, etc. Think of the last car that you bought. The defects in each sample group are counted and run through some statistical calculations. Depending on the type of Attribute Control Chart, the number of defective parts are tracked (p-chart and np-chart), or alternatively, the number of defects are tracked (u-chart, c-chart).

P-Charts

The p-Chart, also known as the Fraction Defective Parts Chart, is the most common of the Attribute Control Charts. For a sample subgroup, the number of defective parts is measured and plotted as a fraction of the total subgroup sample size. It is used for variable and constant sample size

NP-Chart

The np=Chart is also known as the Number Defective Parts, and Number Non-Conforming Parts Chart For a sample subgroup, the number of defective parts is measured and plotted as a simple count. It is used for constant sample size

U-Chart

The u-Chart is also known as the Number of Defects per Unit or Number of Nonconformities per Unit Chart. For a sample subgroup, the number of times a defect occurs is measured and plotted as either a percentage of the total subgroup sample size, or a fraction of the total subgroup sample size. It is used for variable and constant sample size

C-Chart

The u-Chart is also known as the Number of Defects per sample or Number of Nonconformities per sample Chart. For a sample subgroup, the number of times a defect occurs is measured and plotted. It is used for constant sample size

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# "Number defects or nonconformities" control charts (c-charts) can only be used with variable sample sizeA. TrueB. False

B. False

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# Number of nonconforming control charts are called as np-chart.A. TrueB. False

A. True

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# The 3 – sigma upper limit for a control chart for average number of nonconformities per unit, is expressed by ___________a) UCL=u ̅+3√(u ̅/n)b) UCL=u ̅-3√(u ̅/n)c)  UCL=u ̅-2√(u ̅/n)d) UCL=u ̅-3/2 √(u ̅/n)

a) UCL=u ̅+3√(u ̅/n)

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# The sample for the control chart for nonconformities is assumed to have, a variable sample size, and the sample conformities distributed according to Normal distribution.a) Trueb) False

b) False

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# If xi=total number of nonconformities in a sample of ni inspection units, and there are N samples of different sample size, and x varies according to a Poisson distribution, what will be the value of center line of the u-chart?a) u ̅=(∑_(i=1)^N▒〖2x〗_i/n_i )/Nb)   u ̅=(∑_(i=1)^N▒x/〖2n〗_i )/2Nc)  u ̅=(∑_(i=1)^N▒x_i/n_i )/Nd u ̅=(∑_(i=1)^N▒x_i/n_i )/2N

c)  u ̅=(∑_(i=1)^N▒x_i/n_i )/N

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