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Sequential sampling plans for inspection by attributes

Basic Information

Standard ID: GB/T 8051-2008

Standard Name:Sequential sampling plans for inspection by attributes

Chinese Name: 计数序贯抽样检验方案

Standard category:National Standard (GB)

state:in force

Date of Release2008-07-28

Date of Implementation:2009-01-01

standard classification number

Standard ICS number:Sociology, Services, Organization and management of companies (enterprises), Administration, Transport>>Quality>>03.120.30 Application of statistical methods

Standard Classification Number:Comprehensive>>Basic Subjects>>A41 Mathematics

associated standards

alternative situation:Replace GB/T 8051-2002

Procurement status:IDT ISO 8422:2006

Publication information

publishing house:China Standards Press

Plan number:20064616-T-469

Publication date:2009-01-01

other information

Release date:1987-07-08

drafter:Zhang Yuzhu, Yu Zhenfan, Ding Wenxing, Chen Min, Feng Shiyong, Ma Yilin, Wang Renguan, Fu Tianlong

Drafting unit:China National Institute of Standardization, PLA Ordnance Engineering College, etc.

Focal point unit:National Technical Committee for Application of Statistical Methods and Standardization

Proposing unit:China National Institute of Standardization

Publishing department:National Standardization Administration

competent authority:National Standardization Administration

Introduction to standards:

This standard specifies the inspection schemes and procedures for sequential sampling of discrete individual products by counting. This standard uses the retrieval schemes for producer risk points and user risk points. These schemes are not only applicable to the purpose of acceptance sampling, but also to the statistical test of simple assumptions about ratios. The purpose of this standard is to provide a sequential evaluation procedure for inspection results, which can be used to put economic and psychological pressure on producers by rejecting inferior batches, prompting them to provide high-quality batches with a high probability of acceptance. At the same time, an upper limit is set for the probability of acceptance of inferior batches to protect users. GB/T 8051-2008 Inspection schemes for sequential sampling of counting GB/T8051-2008 Standard download and decompression password: www.bzxz.net
This standard specifies the inspection schemes and procedures for sequential sampling of discrete individual products by counting. This standard uses the retrieval schemes for producer risk points and user risk points. These schemes are not only applicable to the purpose of acceptance sampling, but also to the statistical test of simple assumptions about ratios. The purpose of this standard is to provide a sequential assessment procedure for inspection results, which can be used to put economic and psychological pressure on the manufacturer by rejecting inferior batches, prompting it to provide high-quality batches with a high probability of acceptance. At the same time, an upper limit is set for the probability of acceptance of inferior batches to protect the user.
This standard is equivalent to ISO8422:2006 "Sequential sampling inspection plan for attributes".
This standard replaces GB/T8051-2002. Compared with GB/T8051-2002, the main changes in the technical content of this standard are:
---The manufacturer's risk quality and the user's risk quality are changed to priority numbers and expanded.
---The values ​​of the parameters HA, HR and G of the provided scheme are recalculated to accurately meet the specified requirements.
---The user risk quality of the two tests of percentage of non-conforming products and number of non-conforming products per hundred units are separated from the main table and the average sample size of the sequential sampling plan is added to Table A.1.
---Cancel Appendix A on sequential sampling inspection of continuous batches in GB/T8051-2002. This part will be published as GB/T6378.5 after revision.
---Delete Appendix B and Appendix C in GB/T8051-2002, which are mathematically strong and have little to do with the use of the standard.
---The newly added Appendix A is an informative appendix, which gives the statistical characteristics of the sequential sampling inspection plan for attributes.
---Change the general method specified in 6.1 and 6.2 in ISO8422:2006 to the general method specified in 6.2 and 6.3.
--- Expanded the table of numerical examples in Chapter 8.
Appendix A of this standard is an informative appendix.
This standard is proposed by the China National Institute of Standardization.
This standard is under the jurisdiction of the National Technical Committee for Standardization of Statistical Method Application.
Drafting units of this standard: Ordnance Engineering College of the Chinese People's Liberation Army, China National Institute of Standardization, Institute of Mathematics and Systems Science of the Chinese Academy of Sciences, Soochow University, Fuzhou Chunlun Tea Co., Ltd.
Main drafters of this standard: Zhang Yuzhu, Yu Zhenfan, Ding Wenxing, Chen Min, Feng Shiyong, Ma Yilin, Wang Renguan, Fu Tianlong.
The previous versions of the standards replaced by this standard are:
--- GB/T8051-1987, GB/T8051-2002.
The clauses in the following documents become the clauses of this standard through reference in this standard. For any dated referenced document, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, parties that reach an agreement based on this standard are encouraged to study whether the latest versions of these documents can be used. For any undated referenced document, the latest version is applicable to this standard.
GB/T2828.1-2003 Sampling procedures for inspection by attributes Part 1: Sampling plans for batch inspection indexed by acceptance quality limit (AQL) (ISO2859-1:1999, IDT)
ISO3534-1:2006 Statistical vocabulary and symbols Part 1: General statistical terms and terms used in probability
ISO3534-2:2006 Statistical vocabulary and symbols Part 2: Applied statistics
Foreword I
Introduction II
1 Scope 1
2 Normative references 1
3 Terms and definitions 1
4 Symbols and abbreviations 5
5 Principles of sequential sampling inspection plans for attributes 5
6 Selection of sampling plans 6
6.1 Risk points for producers and users 6
6.2 Preferred values ​​of QPR and QCR6
6.3 Preparation before testing6
7 Implementation of a sequential sampling plan6
7.1 Definition of the plan6
7.2 Drawing samples6
7.3 Counting and accumulating numbers6
7.4 Choosing between numerical and graphical methods6
7.5 Numerical methods7
7.6 Graphical methods7
8 Numerical examples8
9 Tables9
Appendix A (Informative) Statistical properties of sequential sampling test plans with attributes16
References21

Some standard content:

ICS 03.120.30
National Standard of the People's Republic of China
GB/T8051—2008/IS08422:2006
Replaces GB/T8051—2002
Sequential sampling plans for inspection by attributes(ISO8422.2006,IDT)
Published on 2008-07-28
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China Administration of Standardization of the People's Republic of China
Implemented on 2009-01-01
CB/T 8051-2008/1SO 8422:2006 Foreword
2 Normative references
3 Terms and definitions
4 Symbols and abbreviations
5 Principles of sequential sampling inspection schemes by attributes
6 Selection of sampling schemes
6.1 Risk points for producers and users Qr and priority values ​​of QcR
Preparation before inspection
Implementation of sequential sampling plan
Provisions of the plan
Sample drawing
Counting and cumulative number
Choice between numerical method and graphical method
Numerical method
Graphical method
Numerical example
Appendix A (informative)
Statistical characteristics of sequential sampling inspection plan for goods with attributes References
This standard is equivalent to ISO8422:2006 Sequential sampling inspection plan for attributes". GB/T 8051-—2008/IS08422.2006 This standard replaces GB/T80512002. Compared with GB/T8051—2002, the main changes in the technical content of this standard are: the producer risk quality and the user risk quality are changed to priority numbers and extended. --…The values ​​of the parameters hA, and g of the scheme provided have been recalculated to accurately meet the specified requirements. The user risk of the two tests of percentage of nonconforming products and number of nonconforming products per hundred units have been separated from the main table and the half-mean sample size of the sequential sampling scheme has been added to Table A, 1. --Cancel Appendix A on the sequential sampling test of continuous batches in GB/T8051-2002. This part will be published as GB/T6378.5 after revision.
Deleted Appendix B and Appendix C of GB/T8051--2002, which are mathematically strong and have little to do with the use of the standard. The newly added appendix is ​​an informative appendix, which gives the statistical characteristics of the sequential sampling test scheme for counting. -:Changed "the general method specified in 6.1 and 6.2" in 6.1 of [508422:2006" to "the general method specified in 6.2 and 6.3"
Expanded the table of numerical examples in Chapter 8.
Appendix A of this standard is an informative appendix. This standard was proposed by China National Institute of Standardization. This standard is under the jurisdiction of the National Technical Committee for the Application of Statistical Methods. The drafting units of this standard are: PLA Ordnance Engineering College, China National Institute of Standardization, Institute of Mathematics and Systems Science of the Chinese Academy of Sciences, Soochow University, and Fuzhou Chunlun Tea Co., Ltd. The main drafters of this standard are: Zhang Yuzhu, Yu Zhenfan, Ding Wenxing, Chen Min, Feng Shiyong, Ma Yilin, Wang Renguan, and Fu Dalong. The previous versions of the standards replaced by this standard are: ---G3/T 8051—1987, GB/T 8051—2002. GH/T 8051—2008/IS0 8422:2006 Introduction
In the modern cattle production process, the defective product rate often reaches the commercial quality level of one part per million (10-10). In this case, the use of an abnormal sampling plan, such as that provided by GB/T2828.1, often requires an extraordinary sample size. Faced with this problem, users will use acceptance sampling plans with a higher probability of misjudgment, or in extreme cases, completely abandon the acceptance sampling procedure. However, in many cases, it is still necessary to accept high-quality products using standardized statistical methods. At this time, a statistical sampling method with the smallest possible sample size should be applied. Sequential sampling plans are the only statistical sampling methods that meet this need, because among all possible sampling plans with similar statistical characteristics, sequential sampling plans have the smallest average sample size. The main advantage of sequential sampling plans is that they can reduce the average sample size. The average sample size is the weighted average of all possible samples of its sampling plan under a given batch or process quality level. Under the premise of equivalent operating characteristics, like secondary and multiple sampling plans, sequential sampling plans have a smaller average sample size than single sampling plans. Using sequential sampling plans saves more average costs than using secondary or multiple sampling plans. For very good quality lots, the savings for sequential sampling schemes can be up to 85%, compared to 37% for subsampling schemes and 75% for multiple sampling schemes. On the other hand, when using subsampling, multiple or sequential sampling schemes, for certain quality lots, the number of units actually tested may exceed the sample size n of the corresponding single sampling scheme. For single and multiple sampling schemes, the upper limit of the number of units actually tested is about 1.25n. For classic sequential sampling schemes, there is no upper limit, and the number of units actually tested can exceed the sample size n of the corresponding subsampling scheme and can even be as large as the batch size N. The sequential sampling plan of this standard introduces the truncation rule, and the upper limit of the number of unit products actually inspected is n. Other factors that need to be considered include:
a) Simplicity
Compared with the simple rules of the one-time sampling plan, the rules of the sequential sampling plan are slightly more complicated. Variability of the inspection quantity
For a specific batch, since the number of unit products actually inspected is not known in advance, there will be some difficulties in the organization and implementation of the sequential sampling plan, such as the arrangement of the inspection operation process. Cost of sampling sample products
If the cost of sampling sample products at different times is high, then the benefit of the reduction in the average sample size of the sequential sampling plan will be offset by the increase in sampling costs.
Duration of the test
If the test time of a single product is long and multiple products can be tested at the same time, the sequential sampling plan will take longer than the corresponding one-time sampling plan.
c) Variation of the quality within the batch
If the batch consists of two or more sub-batches from different sources, and there may be substantial differences in quality between the sub-batches, it is more difficult to extract a representative sample for a sequential sampling plan than for the corresponding single sampling plan. The advantages and disadvantages of the single and multiple sampling plans are between those of the single and sequential sampling plans. Weighing the advantages of the small average sample size against the above disadvantages, it can be concluded that the sequential sampling plan is suitable for situations where the testing cost of a single sample product is relatively expensive. The choice of the type of single, double, multiple and sequential sampling plan should be determined before the batch inspection begins. During the inspection of a batch, it is not allowed to switch from one type to another type, because the operating characteristics of the sampling plan may change drastically if the actual inspection results affect the choice of acceptance criteria.
Although the sequential sampling plan is more economical on average than the corresponding single sampling plan, for the inspection of a specific batch, it may happen that the cumulative number of nonconforming products is long-term between the acceptance number and the rejection number, and the acceptance or rejection decision can only be made when the inspection volume is very large. When the graphical method is used, the above situation corresponds to the step curve being randomly arranged in an indefinite domain. This situation is most likely to occur when the quality level of the batch or process (fraction of defective products or number of defective products per 100 units) is close to 100 times the slope of the acceptance line and the rejection line. To avoid the above situation, a truncated value of the cumulative sample size should be set before the sampling begins. When the cumulative sample size reaches n, if the acceptability of the batch has not been determined, the inspection is terminated, and the acceptance of the batch is determined by the truncated acceptance number and the truncated rejection number. Although truncation will lead to changes in the operating characteristics of the sequential sampling plan, this standard considers truncation when determining the operating characteristics of the sequential sampling plan. The truncation criterion is an integral part of the sampling plan provided by this standard. GB/T2828.5 also provides sequential sampling inspection plans for attributes, but the design principles of those plans are essentially different from those of this standard. The sequential sampling plans in GH/T2828.5 are a supplement to the GB/T2828.1 acceptance sampling system by attributes. Therefore, they are used for the inspection of consecutive batches, and the batch series should be long enough to allow the application of the transfer rules of the GB/T2828 system. When using GB/T2828.5, the application of the transfer rule only means that the user is provided with higher protection (by tightening the sampling inspection or suspending the inspection rules). However, in some cases, it is necessary to control the risks of cattle producers and users more strictly. For example, when the sampling plan is used to assess the quality of the production process or to test the hypothesis, it belongs to this case. In these cases, the individual sampling plans of the GB/T2828.5 sampling plan should not be used. The sampling plans provided by this standard meet this specific need. 1 Scope
Sequential sampling inspection plan with attributes
This standard specifies the sequential sampling inspection plan and procedures for discrete individual products with attributes. GB/T8051—2008/1SO8422:2006
This standard does not use the producer risk point and user risk point retrieval plan. These plans are not only suitable for acceptance sampling purposes, but also for statistical testing of simple hypotheses about comparison ratios. The purpose of this standard is to provide a sequential assessment procedure for inspection results, which can be used to put economic and psychological pressure on producers by rejecting inferior batches, prompting them to provide high-quality batches with a high probability of acceptance. At the same time, an upper limit is set for the probability of acceptance of inferior batches to protect the user. The sampling plan provided in this standard can be used for (not limited to) the following inspections: - Final products; - Parts and raw materials; - Operations; - Work in progress; - Inventory; - Maintenance operations; - Data or records. - Management procedures. The sampling plan of this standard is suitable for counting inspections of discrete individuals. It is used in situations where the defective rate (or percentage of defective products) or the number of defectives per unit of product (or the number of defectives per hundred units of product) is a batch quality indicator. The sampling inspection plan is based on the assumption that the generation of non-conformities is random and statistically independent. If there is a definite reason to suspect that a product failure is caused by a condition that may also cause other failures, it is best to consider only whether the product is a conforming product or a nonconforming product, without considering multiple failures.
The sampling plans recommended by this standard should be used primarily for the analysis of samples taken from the process. For example, these sampling plans are called acceptance sampling for product batches under statistical control. They can also be used for isolated batches with large batches and a small proportion of failures (significantly less than 10%). For acceptance sampling of consecutive serial batches, the batch-by-batch inspection sequential sampling plan system retrieved by acceptance quality limit (AQL) in GB/T 2828.5 should be used.
2 Normative references
The provisions of the following documents become the provisions recommended by this standard through reference in this standard. For any referenced document with an extension period, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, parties to an agreement based on this standard are encouraged to study whether the latest versions of these documents can be used. For undated references, the latest version shall apply to this standard. GB/T2828.1-2003 Sampling procedures for inspection by attributes Part 1: Sampling plans for inspection by lot based on acceptance quality limit (AQL) (ISO 2859-1: 1999, IDT)
IS03534-1, 2006 Statistical vocabulary and symbols Part 1: General statistical terms and technical terms used in probability ISO3534-2: 2006 Statistical vocabulary and symbols Part 2: Applied statistics 3 Terms and definitions
GB/T2828.12003,1ISO3534-1: 2006, ISO3534-2: 2006 The terms, definitions and symbols determined by ISO3534-1: 2006 and ISO3534-2: 2006 and the following terms, definitions and symbols apply to this standard.
GE/T8051—2008/ISO 8422:20063. 1
Inspoction
Conformity assessment by observation and, where appropriate, by simultaneous measurement, test or measurement. [1ISO 3534 2.2006,4. 1. 2
Inspoction by attributes An inspection by which the number of occurrences of one or more specific attributes on each product in the set of products under consideration is recorded, and the number of units with or without the attribute is counted, or the number of such occurrences on the units of a product, set of products or opportunity space is counted (3.1).
Note: When the inspection performed only records whether the unit product is a nonconforming product, it is called an inspection of nonconforming products. When the inspection performed is the total number of nonconforming items on each sampling unit, it is called an inspection of the number of nonconforming items. :ISO 3534-2.2006,4, 1.3
Unit product item (entity)
Anything that can be described and considered individually. Examples: a discrete physical entity; a certain amount of bulk material; a service, activity, person, system or any combination thereof. ISO 3534-2:2006,1. 2. 117
nonconformity
Failure to meet specified requirements.
[GB/T 19000--2000,3. 6.2]Note: See note to 3.5.
defect
Failure to meet the requirements of the intended use.
Note 1: There is a significant difference in the legal connotations between defect and nonconformity (3.4), especially when it comes to liability arising from the product. Therefore, the term defect should be used with extreme caution.
Note 2: The use agreed by the consumer is affected by natural consequences such as operation or maintenance provided to the consumer. [ISO 3534-2: 2006, 3. 1. 127
gnonconforming item
nonconforming product
a unit of product (3.3) with one or more nonconforming (3.1). ISO 3534-2:2006, 1, 2. 12-
percent nonconforining
(sample) fraction of nonconforming items
(in sample) the number of nonconforming items (3.6) in the sample (3.13), divided by the sample size (3.14), multiplied by 100, that is, 100
Wu Zhong:
d----the number of nonconforming items in the sample
n——the maximum number of samples.
[GB/T 2828.1-2003, 3.1.8-
(overall or batch) percentage nonconforming (overall or batch) The number of nonconforming products (3.6) in the whole or batch (3.11) divided by the total quantity or batch size (3.12), multiplied by 100, that is, 2
Where:
Overall (or batch) nonconforming rate;
D,——number of nonconforming products in the whole or batch N
Overall or batch size,
Note 1: Applicable to GB/T 2828. 1-2003, 3. 1. 9. D
100xpe.-100x
GB/T 8051—2008/IS0 8422:2006 Note 2: In this standard, the terms percentage of nonconforming items (3.7 and 3.8) or number of nonconforming items per 100 units of products (3.9 and 3.10) are mainly used. In theoretical situations, the terms "nonconforming rate" and "number of nonconforming items per unit of products" are often used, while the previous terms are more widely used [GB/T 2828. 1—2003, 3. 1.9]
(sample) Number of nonconformities per 100 units of products
nonconformities per 10d items(in sample) The number of nonconformities (3.4) in the sample (3.13) divided by the sample size (3.13), and then multiplied by 100, that is, 100xd
number of nonconformities in the sample;
sample size.
[GB/T 2828. 1—2003,3. 1, 10]3.10
(Total or batch) noncnnfarmitics per 100 items (Total or batch) The number of nonconforming items in the total or batch (3.4) divided by the total quantity or batch size (3.12), and then multiplied by 100, that is, D
100×p=—100×
Where:
P——number of nonconforming items per unit product;
D—number of nonconforming items in the total or batch;
N. Total or batch size
Note 1: ~ unit product may contain one or more nonconforming items. [GB/T2828.12003,3.1.11]
lot
For the purpose of sampling inspection, a collection of unit products consisting of meters. Note:The purpose of sampling inspection may be to determine the acceptability of a lot or to estimate the mean of an individual characteristic. [IsO3534-2:2006,1.2.1]
lot size
the number of units of product (3.3) in a lot (3.11). [GB/T 2828. 2—2008,3. 1. 14]3.13
sample
a subset of one or more sample units from a population. [ISO 3534-2.2006,1. 2. 17
CB/T 8051--2008/ISO 8422.20063. 14
sample size
the number of sample units in a sample.
[150 3534-2:2006,1. 2. 26]
acceptance sampling plan
acceptance sampling plan
sample size (3.14) to be used and the lot acceptance criteria associated with it. [150 3534-2:2006,4. 1,8]
consumer's risk quality
consumer's risk quality
For an acceptance sampling plan (3.15), the quality level of a lot (3.11) or process that corresponds to a specified consumer risk. NOTE The specified consumer risk is typically 10%. [150 3534-2:2006,1. 6. 9]
producer's risk qualityFor an acceptance sampling plan (3.15), the quality level of a lot (3.11) or process that corresponds to a specified producer risk NOTE: The specified producer risk is generally 5% [ISO 3534-2.2006, 4.6.10]
The test result of each sample product when performing an attribute test. NOTE: For the test of nonconforming products, if the sample product is qualified, it is recorded as 1. For the test of the number of nonconforming products, it is the number of nonconforming products found in the sample products. 3.19
cumulative ount
When implementing a sequential sampling test, the sum of the counts from the start of the test to the current sample product being tested. 3.20
cumulative sample sizeWhen implementing a sequential sampling test, the total number of samples from the start of the test to the current sample product being tested. 3.21
acceptance value
The value used to determine the acceptance of a lot in the graphical method of sequential sampling, obtained from the parameters specified in the sampling plan and the cumulative sample. 3.22
Acceptance number
(The number used to determine whether a batch is accepted in the numerical method of sequential sampling, obtained by rounding down the acceptance value. 3.23wwW.bzxz.Net
Rejection value
The value used to determine whether a batch is not accepted in the graphical method of sequential sampling, obtained by the parameters specified in the sampling plan and the product sample size. 3.24
Rejection number
(The number used to determine whether a batch is not accepted in the numerical method of sequential sampling, obtained by rounding up the acceptance value. 3.25
Acceptability table
The table used to determine the acceptability of a batch in the numerical method of sequential sampling. 4
Acceptability chartGB/T 8051—2008/ESO 8422 :2006 (Sequential Sampling) The diagram used to determine the acceptability of a batch in the graphical method consists of the following regions: the acceptance region;
.--a rejection region;
an indeterminate region.
Its boundaries are the acceptance line, the rejection line and the intercept line. 4 Symbols and abbreviations
The symbols and abbreviations used in this standard are as follows: A Acceptance value (for sequential sampling plans)
Ac Acceptance number
Ac The acceptance number of the corresponding sampling plan
The acceptance number at the time of truncation
d Count
D Product number
The slope of the acceptance line and the rejection line
The intercept of the acceptance line
The intercept of the rejection line Intercept
noSample size corresponding to a single sampling plan
Cumulative sample size
Cumulative sample size at truncation
Process average
Quality level with acceptance probability
PAcceptance probability (expressed in percentage)
QcRUser risk quality (expressed as percentage of nonconforming products or number of nonconforming products per 100 units)QpProducer risk quality (expressed as percentage of nonconforming products or number of nonconforming products per 100 units)RRejection value (sequential sampling plan)
ReRejection number
ReuRejection number corresponding to a single sampling plan
RctRejection number at truncation
Note: Re,= Ac. + 1
Risk of the producer
Risk of the user
5Principle of the sequential sampling inspection plan for counting
In the sequential sampling inspection for counting, sample products are randomly selected and inspected one by one, and the number of non-conforming products (or non-conforming numbers) is recorded by cumulative numbers. After inspecting each unit product, the cumulative number is compared with the acceptance criteria to evaluate whether there is enough information to make a decision on the inspection lot at this inspection stage.
At a certain inspection stage, if the cumulative number shows that the risk of accepting a batch with an unsatisfactory quality level is low enough, the batch is accepted and the inspection is terminated. On the other hand, if the cumulative number shows that the risk of rejecting a batch with a satisfactory quality level is low enough, the batch is not accepted and the inspection is terminated. If the above decision cannot be made based on the cumulative number, another unit product is sampled for inspection until there is enough information to make a decision on whether to accept or not accept the batch.
CB/T 8051—2008/IS0 8422:20066 Selection of sampling plan
6.1 Producer risk point and user risk point When two points of the operating characteristic curve required for the sequential sampling plan are specified, the general methods specified in 6.2 and 6.3 can be used. The point with a high probability of acceptance is the producer risk point: the other point is the user risk point. When the two points on the (C curve are not determined, the first step in designing a sequential sampling plan is to determine these two points. For this purpose, the following combinations are often used:
... Producer risk α≤0.05, corresponding producer risk quality (Qp): - User risk 8≤0.10, corresponding user risk quality (Qc) If the sequential sampling plan used has similar operating characteristics to the known one-time, two-time or multiple sampling plans, the risk points of the producer and user can be found from the operating characteristic curve chart of the corresponding plan. If such a plan does not exist, the risk points of the producer and user can only be directly specified based on the requirements for the sampling plan. The priority values ​​of 6.20 and 0
Tables 1 and 2 give the priority values ​​of 28 Q (producer risk quality) ranging from 0.020%) to 10.0%): 23 priority values ​​of Qc (user risk quality) ranging from 0.200 (%) to 31.5 (%). This standard is only used when Qrk and Q are both preferred values ​​and are within the limits of ≤0.05 and ≤0.10. 6.3 Preparation before inspection
6.3.1 Finding the alternative numbers ha, h and g
For each stage of inspection, the acceptance or rejection of the batch is determined by the parameters h. h and g. Tables 1 and 2 give a set of parameters corresponding to the preferred values ​​of Q and Q and the manufacturer's risk α≤0.05 and the user's risk β≤0.10. Table 1 is applicable to the inspection of the percentage of nonconforming products, and Table 2 is applicable to the inspection of the number of nonconforming products per hundred units. 6.3.2 Finding the truncated value
The truncated cumulative sample size nt and the truncated acceptance number Act of the sequential sampling plan are given in Tables 1 and 2 together with the parameters ha, hk and g. 7 Implementation of Sequential Sampling Plan
7.1 Provisions of the Plan
Before implementing the sequential sampling plan, the inspector shall record the specified parameter values, h, g, and the truncated sample size n, and the truncated acceptance number Act in the sampling document.
7.2 Sampling
A sample product shall be randomly bundled from the inspection lot and inspected one by one in the order of sampling: 7.3 Counting and Cumulative Number
7.3.1 Counting
For the inspection of the number of non-conforming products, if the sample product is non-conforming, the count d=1 otherwise d=0. For the inspection of the number of non-conforming products per unit, it is the number of non-conforming products found on the sample product. 7.3.2 Cumulative Number
Cumulative Number D.It is the sum of the d values ​​counted from the first to the most recent sample product (i.e., neum) tested. 7.4 Choice between numerical and graphical methods
This International Standard provides two methods for implementing sequential sampling plans: numerical and graphical methods, from which one can be selected. The numerical method uses acceptance tables, which have the advantage of being accurate and avoiding disputes over acceptance or non-acceptance in marginal cases. The acceptance table can also record the test results in meters.
The graphical method uses acceptance charts, which have the advantage of showing batch quality information by broken lines in an indefinite region on the chart, whose information increases as the number of sample products tested increases until the broken lines reach or cross the boundary line. On the other hand, this method is not very accurate because the plotting of points and lines is inherently not very accurate.
GB/T 8051—2008/IS0 8422:2006 Whenever questions about acceptance or non-acceptance are involved, the numerical method is the standard method (see the warning in 7.6.2). When applying the numerical method, it is recommended to use appropriate software for the calculation and preparation of the acceptance table. 7.5 Numerical method
7.5.1 Preparation of the acceptance table
When using the numerical method, the following calculations should be performed and the acceptance table should be prepared. For each value of ncum, when the cumulative sample size is less than the truncated sample base, the acceptance value A is given by formula (1): A = (gXnmm)-ha
The acceptance number Ac is obtained by rounding down the acceptance value A. For each value of neum, the rejection value R is given by formula (2): R = (gXncumn) + hr
The rejection number Rc is obtained by rounding up the rejection value R. (1)
++*(2)
If the value A obtained by formula (1) is negative, the acceptance of the inspection lot cannot be determined because the cumulative sample size is too small. On the contrary, for the percentage inspection of nonconforming products, if the R value obtained by formula (2) is greater than the cumulative sample size, the cumulative sample size is too small to make a rejection decision for the inspection batch.
If the rejection number Re is greater than the truncated rejection number Re, Re should be replaced by Re, because there is no possibility of acceptance if the cumulative number D reaches or exceeds the truncated rejection number Re.
The A and R calculated in formula (1) and formula (2) should have the same number of decimal places as g. Even if every sample product has been qualified so far, the minimum cumulative sample size is less than hA/g, and the acceptance decision cannot be made; even if every sample product has been unqualified so far, the minimum cumulative sample size is less than or equal to h/(1-g), and the non-acceptance decision cannot be made.
Finally, by recording the necessary values ​​mentioned above, the preparation of the acceptability table is completed. 7.5.2 Determination
After each sample product is inspected, fill in the record value and the cumulative number into the acceptance table prepared in 7.5.1. a) For the cumulative sample size neuum, if the cumulative number D is less than or equal to the corresponding acceptance number Ac, the batch is accepted and the inspection is terminated. b) For the cumulative sample size ncum, if the cumulative number D is greater than or equal to the corresponding rejection number Rc, the batch is not accepted and the inspection is terminated. c) If neither a) nor b) is satisfied, continue to draw the next sample product for inspection: When the cumulative sample size reaches the truncated sample size tl, the truncated acceptance number Ac and the truncated rejection number Rct (=Ac, +1) should be used in rules a) and b) respectively.
7.6 Graphical method
7.6.1 Preparation of acceptance diagram
When using the graphical method, the acceptance diagram should be prepared according to the following steps. In the rectangular coordinate system, the cumulative sample size n is the horizontal axis and the case cumulative number D is the vertical axis. Draw two straight lines with slope g in the figure. The lower straight line is the acceptance line, the intercept is HA, and the ordinate value corresponds to the acceptance value of formula (1); the upper straight line is the rejection line, the intercept is h, and the ordinate value corresponds to the rejection value R of formula (2). Add a vertical line at num-n as the truncation line. A horizontal line is added at DRer as the cut-off line. These lines in the figure determine the following regions: Acceptance region: the acceptance line and the area below it, together with the point on the truncation line (nAc) and the part below it; Rejection region: the rejection line and the area above it, together with the point on the truncation line (nAc) and the part above it; Unacceptable region: the strip area to the left of the truncation line between the acceptance line and the rejection line. After adding the cut-off line, the triangular area (including each boundary) bounded by the rejection line, the truncation line and the cut-off line in the upper part of the unacceptable region is part of the rejection region. All points representing the cumulative number in Figure 1 of this standard do not fall on the acceptance line or the rejection line. Figure 1 is an example of a prepared acceptability diagram.The cumulative sample size n is the horizontal axis and the case volume D is the vertical axis. Draw two straight lines with slopes of g in the figure. The lower straight line is the acceptance line, the intercept is -HA, and the ordinate value corresponds to the acceptance value of formula (1); the upper straight line is the rejection line, the intercept is h, and the ordinate value corresponds to the rejection value R of formula (2). Add a vertical line at num-n as the truncation line. A horizontal line is added at DRer as the cut-off line. These lines in the figure determine the following regions: Acceptance region: the acceptance line and the area below it, together with the point on the truncation line (nAc) and the part below it; Rejection region: the rejection line and the area above it, together with the point on the truncation line (nAc) and the part above it; Unacceptable region: the strip area to the left of the truncation line between the acceptance line and the rejection line. After adding the cut-off line, the triangular area (including each boundary) bounded by the rejection line, the truncation line and the cut-off line in the upper part of the unacceptable region is part of the rejection region. All points representing the cumulative number in Figure 1 of this standard do not fall on the acceptance line or the rejection line. Figure 1 is an example of a prepared acceptability diagram.The cumulative sample size n is the horizontal axis and the case volume D is the vertical axis. Draw two straight lines with slopes of g in the figure. The lower straight line is the acceptance line, the intercept is -HA, and the ordinate value corresponds to the acceptance value of formula (1); the upper straight line is the rejection line, the intercept is h, and the ordinate value corresponds to the rejection value R of formula (2). Add a vertical line at num-n as the truncation line. A horizontal line is added at DRer as the cut-off line. These lines in the figure determine the following regions: Acceptance region: the acceptance line and the area below it, together with the point on the truncation line (nAc) and the part below it; Rejection region: the rejection line and the area above it, together with the point on the truncation line (nAc) and the part above it; Unacceptable region: the strip area to the left of the truncation line between the acceptance line and the rejection line. After adding the cut-off line, the triangular area (including each boundary) bounded by the rejection line, the truncation line and the cut-off line in the upper part of the unacceptable region is part of the rejection region. All points representing the cumulative number in Figure 1 of this standard do not fall on the acceptance line or the rejection line. Figure 1 is an example of a prepared acceptability diagram.
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