This standard specifies once, twice and quintic sampling plan and sampling program taking nonconforming quality level (expressed with percent nonconforming or nonconformities per 100 items) as the quality index, which applies to the inspection of process stability.
2 Normative References
The following standards contain provisions which, through reference in this text, constitute provisions of this standard. For dated reference, subsequent amendment to (excluding correction to), or revisions of, any of these publications do not apply. However, all parties coming to an agreement according to this standard are encouraged to study whether the latest edition of these documents is applicable. For undated references, the latest edition of the normative document is applicable to this standard.
GB/T 3358.1-1993 "Terms for Statistics-Part I: Terms for General Statistics"
GB/T 3358.2-1993 "Terms for Statistics-Part II: Terms for Statistical Quality Control"
GB/T 28281 "Sampling Procedures for Inspection by Attributes-Sampling Schemes Indexed by Acceptance Quality Limit (AQL) for Lot-by-lot Inspection" (idt ISO 2859-1)
3 Terms, Definitions and Symbols
3.1 Terms and definitions
The established terms and definitions in GB/T 3358 and the following ones are applicable to this standard.
3.1.1
Item
It refers to the basic unit to be classified for implementing the sampling inspection.
For example: single piece product, a pair of products, a group of products, one parts, or the product with a certain length, area, volume and weight. It may be consistent or not with the item specified by purchasing, sales, production and shipment.
3.1.2
Inspection lot (lot)
It refers to the product or service with a certain quantity, which is collected according to a certain condition.
Note: "Lot" in this standard refers to all items inspected and manufactured for production forming, or all items manufactured within one specified period during lot production process after passing through production forming inspection.
3.1.3
Lot size
It refers to the quantity of the item in the lot.
3.1.4
Sample unit
It refers to the item extracted from the lot for inspection.
1) It is in revision process (revision of GB/T 2828-1987 "Sampling Procedures and Tables for Lot-by-lot Inspection by Attributes (Apply to Inspection of Successive Lots or Batches" and is identical to ISO 2859-1:1999.
3.1.5
Sample
It refers to the whole of the sample unit.
3.1.6
Sample number
It refers to the sample unit quantity involved in the sample.
3.1.7
Nonconformity
The quality characteristic of the item does not conform to the specification. The nonconformity is classified according to the significance of the quality characteristic expressing the significance of item quality or the severity of quality characteristic nonconformity, which is generally classified into: Class A nonconformity, Class B nonconformity and Class C nonconformity.
3.1.8
Class A nonconformity
The extremely important quality characteristic of the item does not conform to the specification, or the quality characteristic of the item does extremely severely not conform to the specification.
3.1.9
Class B nonconformity
The important quality characteristic of the item does not conform to the specification, or the quality characteristic of the item does severely not conform to the specification.
3.1.10
Class C nonconformity
The general quality characteristic of the item does not conform to the specification, or the quality characteristic of the item does slightly not conform to the specification.
3.1.11
Nonconforming item
It refers to the unit with one or more nonconformity. It may generally be classified into according to the nonconformity class: Class A nonconforming item, Class B nonconforming item and Class C nonconforming item.
3.1.12
Class A nonconforming item
It refers to the item having one or more than one Class A nonconformity and may include Class B and/or Class C nonconformity.
3.1.13
Class B nonconforming item
It refers to the item having one or more than one Class B nonconformity and may include Class C nonconformity, but exclude Class A nonconformity.
3.1.14
Class C nonconforming item
It refers to the item having one or more than one Class C nonconformity but exclude Class A and Class B nonconformity.
3.1.15
Percent nonconforming
The total number of all nonconforming items in the lot divides by the lot size and then multiply 100. Namely:
Percent nonconforming-(Total number of nonconforming items in the lot)/lot size)×100
3.1.16
Nonconformities per 100 items
The total nonconformity number of all items in the lot divides by the lot size and then multiply 100. Namely:
Nonconformities per 100 items-(Total nonconformity number of all units in the lot/lot size)×100
3.1.17
Lot quality
It refers to the quality of inspection lot with single submission (expressed with percent nonconforming or nonconformities per 100 items).
3.1.18
Rejectable quality level
It refers to the lower limit value of unacceptable lot quality in the sampling inspection.
3.1.19
Inspection
It refers to the activity to determine, inspect and test one or more characteristics and compare with specified requirements in order to determine whether the product or process is qualified.
3.1.20
Inspection by attributes
It refers to the inspection determining whether the item is conforming item or nonconforming item or counting the nonconformities of item according to one group of or one technical requirements specified in the product technology standard.
3.1.21
Lot-by-lot inspection
It refers to the inspection for each lot in the series of lots.
3.1.22
Periodic inspection
It refers to the inspection to extract sample from some lot or several lots with qualified lot-by-lot inspection in order to judge whether the stability of the production process meets the specified requirements within specified period (by time, or by manufactured item quantity).
3.1.23
Production forming inspection
It refers to the periodic and lot-by-lot inspection in order to judge whether a certain production line can manufacture the product meeting the quality requirements by lot.
3.1.24
Lot production inspection
It refers to the periodic and lot-by-lot inspection in order to judge whether a certain production line can maintain to manufacture the products meeting the quality requirements by lot after passing through the production forming inspection.
3.1.25
Conformities
It refers to the maximum number of the permissible nonconformity or nonconforming item in the sample of the conforming lot in attributes acceptance sampling.
3.1.26
Nonconformities
It refers to the minimum number of the permissible nonconformity or nonconforming item in the sample of the nonconforming lot in attributes acceptance sampling.
3.1.27
Distinguishing array
It refers to the combination of the conformities and nonconformities or conformities series and nonconformities series.
3.1.28
Sampling plan
It specifies one specific plan for the sample number and related acceptance criterion.
3.1.29
Sampling program
It refers to the process using the sampling plan to judge lot conforming or not.
3.1.30
Single sampling plan
It refers to the sampling plan composed of the combination of sample number and distinguishing array [Ac, Re].
3.1.31
Twice sampling plan
It refers to the sampling plan composed of the combination of the first sample number n1, the second sample number and distinguishing array [A1, A2, R1, R2].
3.1.32
Quintic sampling plan
It refers to the sampling plan composed of the combination of sample number series n1, n2, n3, n4 and n5 and distinguishing array [A1, A2, A3, A4, A5, R1, R2, R3, R4 and R5].
3.1.33
Distinguishing level
It refers to the grade to distinguish the ability size that the production process stability does not conform to the specified requirements.
3.1.34
Acceptance probability
It has given quality level lot or the probability that the process is judged as qualified when using one determined sampling plan.
3.1.35
Average sample number
It refers to the sample number of the average lot to be inspected when using a certain sampling plan to make conformity or nonconformity decision.
3.1.36
Characteristic curve of random inspection (OC curve)
For the given sampling plan, it expresses the functional relation curve of lot acceptance probability and lot quality level.
3.1.37
Average sample number curve (ASN curve)
For the given sampling plan, it expresses the functional relation curve of average sample number and lot quality level.
3.2 Symbols
N: Lot.
N: Sample number.
Note: When it is necessary to distinguish the first sample number, the second sample number ⋯, respectively plus subscript 1, 2⋯. For example, n5 expresses the fifth sample number.
Ac: Conformities.
Re: Nonconformities.
Note: If it is necessary to distinguish the first, second ⋯conformity and nonconformities, respectively change the subscript c and e into 1, 2⋯. For example, A2 expresses the second conformity; R3 expresses the third nonconformity.
[Ac, Re]: Distinguishing array of single sampling plan.
[A1, A2, R1, R2]: Distinguishing array of twice sampling plan.
[A1, A2, A3, A4, A5, R1, R2, R3, R4, R5]: Distinguishing array of quintic sampling plan.
P: Lot quality.
Pa: Lot acceptance probability.
DL: Distinguishing level.
RQL: Rejectable quality level.
ASN: Average sample number.
