Sampling - Sampling Whysample Finalquality,grade...

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Sampling
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Why sample? Acceptability of raw material Is process working properly? Final quality, grade Often impossible to inspect 100% Take a representative sample Based on statistics Need adequate sample, but not too large Should verify that plan is working
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Definitions Attributes vs. variables Attributes = classify as acceptable or  unacceptable Variables = measure on a scale Types of defects Critical – may be legal issues Constitute a health hazard Toxic substance, microbial problems, severe  loss of quality, etc.
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Definitions Types of defects Major Adverse effects on quality, but not dangerous Insect parts, dented cans, numerous quality changes May affect sales Minor Change in economic value or quality, but not  dangerous Minor quality changes, appearance, container, etc.
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Definitions Types of defects No clear distinction except when  dangerous Even minor defects can add up Bulk vs. sub-lots Bulk is not packaged - truckloads, etc. Sub-lots – pallets, crates, boxes, etc.
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Factors that influence  sampling plans Purpose of inspection Accept or reject Raw materials, etc. = attribute sampling plans Evaluate overall quality Usually variables plan Determine uniformity Usually variables plan
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Factors that influence  sampling plans Nature of material being sampled Homogenity More variability, more samples Unit size Liquids & small particles = use standard unit  size for each sample (wt., vol., etc.) Larger size = 1 unit may serve as a sample Even larger = may have to subdivide 1 unit  (side of beef)
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Factors that influence  sampling plans History of material Tighten or loosen inspection if warranted Cost of sampling and the samples Nature of the test Major or minor characteristic Destructive or non-destructive Time and difficulty of analysis
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Factors that influence  sampling plans Nature of the lot Size of lot Sub-lots How many units from how many sub-lots Must define the population (100 bags, a pallet,  a truckload, 1 day’s production, etc.) Way it is loaded Can make random sampling difficult
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Attribute Sampling Plans Use when determining whether to  accept or reject a population Classify each sample as ok or defective A sampling plan includes: N=lot size N=sample size C=maximum number of defects
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Attribute Sampling Plans Must specify an acceptable quality level  (AQL) % defective you’re willing to tolerate Producer’s risk Probability of rejecting a lot with AQL Consumer’s risk Probability of accepting a lot with AQL
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This note was uploaded on 03/03/2011 for the course FOS 4722 taught by Professor Sims during the Spring '10 term at University of Florida.

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Sampling - Sampling Whysample Finalquality,grade...

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