The control chart indicates when to leave a process alone in order to avoid needless frequent adjustments since variances in the manufacturing process are unavoidable. A suitable sized random sample is taken from each lot, according to the statistical sampling theory, which is the foundation of control charts, which are visual representations. Control charts track processing variations and alert the user if there is a departure from the defined tolerance limits. These control charts enable the quick identification of unwanted deviations as well as the identification and elimination of their causes.

When some items exhibit variation beyond the tolerances in control charts where upper and lower values are defined for a quality feature, the situation is reviewed, and immediate remedial action is done.

The control chart is a tool that helps us keep track of our data so that we can make sure we're getting accurate results. It also helps us make sure that we're making good decisions based on our data.

1. Variable: $\bar{x}$ chart, R-chart
2. Attributes: p-chart, np-chart, C-chart

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Solved Example: 9030-01

Control charts for the attribute are concerned with: (HPCL Engineer Mech Aug 2021 Shift I)

A. Checking if the variable is out of control.

B. The actual measurement of the parameter, comparing with a standard.

C. Qualitative checking of defects.

D. Direct measurement of the variable for control.

Correct Answer: C

Solved Example: 9030-02

Which is the control chart for fraction defective? (MPSC AMVI Paper IV: 2005)

A. V - chart

B. P - chart

C. X - chart

D. C - chart

Correct Answer: B

Solved Example: 9030-03

The chart which is used to monitor the variable is: (JKSSB JE CE Shift II Oct 2021)

A. P-chart

B. Range chart

C. C-chart

D. Q-chart

Correct Answer: A

Solved Example: 9030-04

The probability law used for calculating the control limits of p-chart is: (UPPSC Lecturer Mech Paper I Dec 2021)

A. Poisson

B. Normal

C. Binomial

D. Exponential

Correct Answer: C

Solved Example: 9031-01

An Operating Characteristics curve (OC-curve) is a plot between: (UPPSC AE Mech 2013 Paper I)

A. Consumer's risk and producer's risk

B. Probability of acceptance and probability of rejection

C. Percentage of defective and probability of acceptance

D. Average outgoing quality and probability of acceptance

Correct Answer: C

Solved Example: 9031-02

For the purpose of sampling inspection, the maximum percent defective that can be considered satisfactory as a process average is: (ESE Mech 2020)

A. Rejectable Quality Level (RQL)

B. Acceptable Quality Level (AQL)

C. Average Outgoing Quality Limit (AOQL)

D. Lot Tolerance Percent Defective (LTPD)

Correct Answer: B

Solved Example: 9031-03

Operating Characteristic (OC) curve shows probability of acceptance Vs fraction __: (ISRO IPRC Tech Asst Mech Aug 2016)

A. Acceptable

B. Rejection

C. Defective

D. None of these

Correct Answer: C