ISO 3951 - Sampling procedure for Inspection by Variables Data

B

biju-joseph

#1
Hi
need help on revised iso 3951 sampling procedure for inspection by variable , looks like the new procedure is more complicated and we need to identify the "K" factor and do the calculation to compare to analyze the lot is acceptable or not.
can I use 2859 for variable

thank you in advance

Biju joseph
 
Elsmar Forum Sponsor

Statistical Steven

Statistician
Staff member
Super Moderator
#2
Re: ISO 3951 -sampling procedure for inspection by variable

The short answer is you cannot use 2859 which is for attribute sampling for variable data. Where are you having an issue with 3951. If you look at the example, the calculations are pretty straightforward.
 
W

Waeller

#3
Re: ISO 3951 -sampling procedure for inspection by variable

Hi Statistical Seven,

Thank you for the statement concerning the use of 3951 vs 2859.
But still - I have some questions:

1) E.g.: Measuring a length having an upper and lower spec limit, uncertainty considerations included in the measurement. Isn't it possible to define parts in within spec as "confirming" and out of spec as "non confirming" and use this judgement as attributive and use 2859?

2) Asuming non normality:
Transforming the distribution into normality, means transforming the limits as well. What about the k-factors? Aren't they calculated based on a normal distribution?

Thanks for any hint
Waeller

P.S.
I Would like to ask my company statistician, if there is one!
 

Statistical Steven

Statistician
Staff member
Super Moderator
#4
Re: ISO 3951 -sampling procedure for inspection by variable

Hi Statistical Seven,

Thank you for the statement concerning the use of 3951 vs 2859.
But still - I have some questions:

1) E.g.: Measuring a length having an upper and lower spec limit, uncertainty considerations included in the measurement. Isn't it possible to define parts in within spec as "confirming" and out of spec as "non confirming" and use this judgement as attributive and use 2859?
You can always convert a continuous measurement into a attribute measurements as you described. Understand that the sample size requirement per 2859 is much larger than the 3951 for the same coverage.Not usually worth the additional work (i.e. 200 for attribute versus 33 for variable)

2) Asuming non normality:
Transforming the distribution into normality, means transforming the limits as well. What about the k-factors? Aren't they calculated based on a normal distribution?
Yes they are based on the normal distribution, but the transformation makes your data normal, so the K value is not transformed.
Thanks for any hint
Waeller

P.S.
I Would like to ask my company statistician, if there is one!
Without a company statistician, you should get a consultant or contract statistician on retainer.
 
W

Waeller

#5
Re: ISO 3951 -sampling procedure for inspection by variable

Hi Statistical Seven,

I need to follow up on the ISO-3951 and in addition on 11608-1.
Both need normal distributions to calculate the tolerance limits (x_bar +- K* S).

My question:
Is it possible to judge the tolerance limits - even the distribution is not a normal one - with the equation above?
Wouldn't it be more critical if not centered distributions with higher standard deviations
would be traeted as if they were normal distributions?

Thanks for any hint
Waeller
 

Statistical Steven

Statistician
Staff member
Super Moderator
#6
Re: ISO 3951 -sampling procedure for inspection by variable

The ISO-3951 is based on normality. There are some adjustments for non-normal data, but in general when the data is non-normal it helps to understand the underlying distribution to calculate the sample size.

I use 16269-6 for tolerance intervals. It has the formulas for non-normal tolerance intervals. Be aware that the minimum sample size for non-normal or distribution free tolerance intervals are quite large to get the coverage you desire.

Hi Statistical Seven,

I need to follow up on the ISO-3951 and in addition on 11608-1.
Both need normal distributions to calculate the tolerance limits (x_bar +- K* S).

My question:
Is it possible to judge the tolerance limits - even the distribution is not a normal one - with the equation above?
Wouldn't it be more critical if not centered distributions with higher standard deviations
would be traeted as if they were normal distributions?

Thanks for any hint
Waeller
 
W

Waeller

#7
Hi Statistical Seven,

thank you very much for the fast reply. But as usual 1 answer lead to more questions.

In the 3951 there is a relation between AQL =0,01, n=63 and k=3.2xx for code letters P or Q for the s-method.

In 16296 only ordered statistics are mentioned e.g. v+w for 1 to 20 and a sample size number.
Is there a way to relate a given/definded AQL to this distribution free sample size and/or distribution free 2-sided tolerance limits?

Thank you very much
Waeller

PS
...im still looking for a company statistician ....
 

Statistical Steven

Statistician
Staff member
Super Moderator
#8
Not sure I follow your question, but 3951 does index by AQL. ISO 3951 is for acceptance sampling by variables and the k-values are not the same k-value for tolerance intervals.

16269 gives distribution free and normal tolerance interval methods.

Hi Statistical Seven,

thank you very much for the fast reply. But as usual 1 answer lead to more questions.

In the 3951 there is a relation between AQL =0,01, n=63 and k=3.2xx for code letters P or Q for the s-method.

In 16296 only ordered statistics are mentioned e.g. v+w for 1 to 20 and a sample size number.
Is there a way to relate a given/definded AQL to this distribution free sample size and/or distribution free 2-sided tolerance limits?

Thank you very much
Waeller

PS
...im still looking for a company statistician ....
 
W

Waeller

#9
Hi Statistical Seven,

I'm sorry for not cleary getting to the point. Yes, I'm looking for some acceptance sampling plans or methods.

What do I have to apply, if I have an AQL=0,01 to fullfil and the data of the measured variable is not normal distributed - and can not be transformed into normal data. And the lot size is about 100k to 150k.

e.g destructive Dial Torque meaurements, no target value, only upper and lower limits.
LSL 10mNm
USL 95mNm


Waeller
 

Statistical Steven

Statistician
Staff member
Super Moderator
#10
Hi Statistical Seven,

I'm sorry for not cleary getting to the point. Yes, I'm looking for some acceptance sampling plans or methods.

What do I have to apply, if I have an AQL=0,01 to fullfil and the data of the measured variable is not normal distributed - and can not be transformed into normal data. And the lot size is about 100k to 150k.

e.g destructive Dial Torque meaurements, no target value, only upper and lower limits.
LSL 10mNm
USL 95mNm


Waeller
Waeller

Here are several options, not are better than others, but just how I approach a problem like this.

First I try to under why my data is not normal for a two-sided specification of torque. I expect non-normality with a one-sided specification, but usually do not see normality unless it's bi-modal. If the data is in fact bi-modal, then acceptance testing is a complex issue as you need to know the distribution of the parts from each mode. Without a fundamental understanding of the data, using continuous (either normality or non-normality) acceptance is an exercise in futility.

My usual response is that though we measure torque as a continuous value, we can use attribute based sampling as the parts either pass or don't pass. Again, without a distributional assumption about the data, cannot calculate the mean and standard deviation to predict percent out of specification.

You can use reliability type models to predict probability of exceeding the specification using different sample sizes based on exponential or weibull models. This is NOT a perfect solution, and requires an iterative process for finding the best solution.

Assume normality and use 3951. This is ONLY used if the lack of normality is small and the cause is from "outliers".

Otherwise, I am stumped!
 
Thread starter Similar threads Forum Replies Date
N Sampling Plan for Internal Audits - ISO 2859 or 3951 - Or Neither? Internal Auditing 6
I Alpha and Beta in the Sampling Plan for ISO 2859 & ISO 3951 Inspection, Prints (Drawings), Testing, Sampling and Related Topics 13
F AQL - ISO 3951-4:2011 Sampling Plan Requirements AQL - Acceptable Quality Level 2
M Where to buy ISO 3951-1 and ISO 3951-2 standard copy Other ISO and International Standards and European Regulations 1
P ISO 3951 vs. ISO 2859 for Medical Device Components ISO 13485:2016 - Medical Device Quality Management Systems 2
I Does anyone here have experience with ISO 3951? Other ISO and International Standards and European Regulations 3
P Medical device functional test - ISO 2859 or 3951 Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
S Need help to test my excel worksheet based on ISO 3951 Excel .xls Spreadsheet Templates and Tools 1
E ISO 2895/3951 Switching Inspection Rules Inspection, Prints (Drawings), Testing, Sampling and Related Topics 11
B Employee Handbook in ISO 9001:2015 Section 7 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 13
B Operational Procedures for ISO 13485:2016 ISO 13485:2016 - Medical Device Quality Management Systems 7
Q ISO 9001/IATF 16949 Audit Finding Question - Document Retention IATF 16949 - Automotive Quality Systems Standard 10
D ISO 14971 applicability in ISO 13485 ISO 13485:2016 - Medical Device Quality Management Systems 7
G Trying to get a financially reasonable ISO Certification Body Registrars and Notified Bodies 7
L ISO 45001:2018 - Clause 5.4: Consultation and Participation of Workers Process Maps, Process Mapping and Turtle Diagrams 0
E ISO 13485 in Clinical Trial conduct: Applicable or No ISO 13485:2016 - Medical Device Quality Management Systems 2
G ISO 13485 Certification - Can we get the ISO 13485 certification prior to shipment of the device? ISO 13485:2016 - Medical Device Quality Management Systems 6
Richard Regalado Informational ISO/IEC DIS 27001:2021, to be published soon. IEC 27001 - Information Security Management Systems (ISMS) 0
Q Audit report template ISO 9001/14001 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 13
N Does anyone use SGS for ISO 13485 / CE certification Registrars and Notified Bodies 0
Q Process matrix examples of ISO 9001 & 14001 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
S Need ISO 15189:2012 Documentation toolkit. Document Control Systems, Procedures, Forms and Templates 0
chris1price Archiving of paper records - ISO 9001 7.5.3.1b Records and Data - Quality, Legal and Other Evidence 4
M Transferring ISO 17025 from one company to another ISO 17025 related Discussions 1
D Common practices in ISO 9001 deployment ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 17
Q ISO 9001-2015 Internal audit finding Internal Auditing 12
P Audit check for IT company (ISO 9001) ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 7
M Label Making & Printing Standards ISO / ASTM ISO 13485:2016 - Medical Device Quality Management Systems 5
Sidney Vianna Interesting Discussion Should ISO 9004 be changed from a guidance document to a requirements standard? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 7
Ed Panek ISO 13485:2016 Section 5.5.3 ISO 13485:2016 - Medical Device Quality Management Systems 3
Q Do these certificates of calibration meet ISO 9001 requirements for traceability to NIST? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 12
ebrahim QMS as per ISO 13485, Clause 4.2 Requirements for regulatory purposes for Medical Devices Authorized Representatives. ISO 13485:2016 - Medical Device Quality Management Systems 3
S ISO 2768-mk print call out Other ISO and International Standards and European Regulations 11
T ISO 17024, clauses 4.3.8. and 5.1.1. Other ISO and International Standards and European Regulations 4
C ISO 14001:2015 6.1.3 Compliance Obligations - Legal requirements monitoring ISO 14001:2015 Specific Discussions 0
C Requirement to link Quality Manual to ISO 9001 clause numbers? ISO 13485:2016 - Medical Device Quality Management Systems 13
D ISO 13485 scope (implantable) - Polymers for dental application EU Medical Device Regulations 9
W First time being audited (ISO 9001), asking for advice ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 9
John C. Abnet ISO 26262 ISO 26262 - Road vehicles – Functional safety 3
Marc ISO 26262- Road vehicles – Functional safety ISO 26262 - Road vehicles – Functional safety 0
John C. Abnet ISO 26262 IATF 16949 - Automotive Quality Systems Standard 0
A ISO/DIS 15223-1:2020 - Country of manufacture label (IEC 60417 No. 6049) - Which national law requires this symbol? Other Medical Device Related Standards 0
P ISO 14644 Class 8 Cleanroom Air Filter Requirements Other Medical Device Related Standards 4
K PDCA cycle and ISO processes alternative model Quality Management System (QMS) Manuals 14
N ISO 13485 7.3.9 Change control in medical device software ISO 13485:2016 - Medical Device Quality Management Systems 6
A ISO 13485 procedure change and reflect to legacy manufacture items ISO 13485:2016 - Medical Device Quality Management Systems 2
D ISO 13485 & CE Certification for Surgical Gloves CE Marking (Conformité Européene) / CB Scheme 0
S ISO 11137- Simulated product vs SIP Other Medical Device Related Standards 2
D Which ISO Standard to purchase? ISO 13485:2016 - Medical Device Quality Management Systems 7
V ISO 10360-5: 2020 Gap analysis and Action plan Excel .xls Spreadsheet Templates and Tools 1

Similar threads

Top Bottom