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Questions and Answers
What does a process capability index of 1 indicate?
What does a process capability index of 1 indicate?
Which of the following is a disadvantage of acceptance sampling?
Which of the following is a disadvantage of acceptance sampling?
What is a significant disadvantage of conducting inspections?
What is a significant disadvantage of conducting inspections?
What is the primary purpose of acceptance sampling?
What is the primary purpose of acceptance sampling?
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What characteristic of a large lot size affects the number of defects in single sampling plans?
What characteristic of a large lot size affects the number of defects in single sampling plans?
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What does a stable process with only natural causes of variation indicate about the output?
What does a stable process with only natural causes of variation indicate about the output?
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Which control chart is appropriate for monitoring shifts in central tendency of a variable?
Which control chart is appropriate for monitoring shifts in central tendency of a variable?
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If a process’s upper and lower specification limits are within ± 3 standard deviations from the mean, what does this indicate?
If a process’s upper and lower specification limits are within ± 3 standard deviations from the mean, what does this indicate?
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What is the characteristic of a capable process concerning its Process Capability ratio?
What is the characteristic of a capable process concerning its Process Capability ratio?
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Which type of control chart is utilized for categorical variables?
Which type of control chart is utilized for categorical variables?
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Which statement about R-charts is true?
Which statement about R-charts is true?
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What is the significance of setting control limits at 'three sigma' in control charts?
What is the significance of setting control limits at 'three sigma' in control charts?
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When is a product considered non-conforming according to the c-chart?
When is a product considered non-conforming according to the c-chart?
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Study Notes
Statistical Process Control and Acceptance Sampling
- Control Charts: Visual tools used to monitor a process's output, identifying whether the process is stable (influenced only by common causes of variation) or unstable (affected by special causes).
- Control Limits: Upper and lower control limits are usually set at 3 standard deviations from the mean.
- Central Limit Theorem: Regardless of the underlying distribution, the sampling distribution of the means will approximate a normal distribution for sufficiently large sample sizes.
- X-bar Chart: Used to monitor the central tendency (mean) of a process that measures continuous variables. Detects changes in the process mean.
- R-Chart: Used to monitor the variability (range) of a process that measures continuous variables. Detects changes in the process variability (dispersion).
- P-Chart: Used to monitor the proportion of defective items in a process that measures categorical variables. Based on the binomial distribution.
- C-Chart: Used to monitor the number of defects per unit in a process that measures categorical variables.
Process Capability
- Process in Control vs. Process Capability: A process can be in statistical control (stable) but still produce products outside of desired tolerances. Process capability examines the process's ability to meet specifications.
- Process Capability Ratio: Indicates how many standard deviations fall within the specifications. A ratio of at least 1.0 is desirable, with higher ratios indicating greater capability of meeting specification. Six Sigma quality aims for a ratio of 2.0.
Process Capability Index
- Process Capability Index (Cp): Measures the difference between the actual output and desired specifications. A Cp of 1.0 indicates the process is capable of meeting specifications, and higher values indicate better capability.
Inspection
- Importance of Inspection: Inspection examines items (units/products/services) to identify defects - but without correcting deficiencies in the process, it can be costly.
- When to Inspect: At various stages; while producing, facility upon receipt, before costly/irreversible procedures, production/service complete, before delivery, at customer contact point, etc.
- Problems with Inspection: Includes worker fatigue and measurement errors when done manually.
Acceptance Sampling
- Acceptance Sampling Overview: A plan for inspecting a random sample of items and deciding whether to accept or reject the entire batch.
- Method/Process: Determine a sample size, inspect each item, reject the whole lot if the number of inspected defects exceeds an acceptance number.
- Acceptance Sampling vs. 100% Inspection: Acceptance sampling is less expensive, less handling, avoids destructive tests, and can motivate workers. Disadvantages include risk of accepting bad lots or rejecting good lots.
- Single Sampling Plans: A random sample is taken from a lot. Rejection of the lot occurs based on the sample's defect count.
- Sampling Distributions: For large lots, the number of defects is modeled by a binomial distribution; for smaller lots, it's a hypergeometric distribution.
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Description
Test your knowledge on Statistical Process Control and Acceptance Sampling concepts. This quiz covers key tools like control charts, control limits, and the Central Limit Theorem. Challenge yourself with questions on X-bar, R, and P-charts to see how well you understand process monitoring.
