LTPD (Lot Tolerance Percent Defective) vs. AQL (Acceptable Quality Level) Definitions

Elsmar Forum Sponsor
M

M Greenaway

#2
Both terms are related to sample inspection using standard sampling plans.

AQL is the Acceptable Quality Level, and is the contractually agreed acceptable amount of defects in a batch. So for example an AQL of 0.1 would mean that the customer accepts 0.1% defects in a batch.

LTPD is the Lot Tolerance Percentage Defective - and I am struggling to recall what that is about at the moment !
 
D

Dave Strouse

#3
AQL - LPTD

Johnny , Martin

AQL is as Martin said the mutually agreed on quality level that the customer finds acceptable. Actually, plans based on AQL will not in general produce lots to that AQL.

AQL is the level which will be accepted most of the time. Most generally for ANSI-ASQ V1.4 plans usually means in the 90 to 95% of the time.

The actual long term average of the lots is another measure AOQL, Average Outgoing Quality Level.

LPTD or Lot Percent Tolerant Defective is the level of quality that will be rejected most of the time. Usually for Dodge Romig type plans at 10% probability.


AQL plans should generally be used as short term stop gap measures to control quality to some tolerable level while improvements aree made. Or so my advisor, Ed Schilling indicates in his book on accpeptance sampling.

LPTD will do more to insure high q2uality to any particular level, but the price paid is increased asampling. Management usually does not like this.

Most managers I have worked with believe that they will not get a lot above the AQL using this kind of a plan. They are usually surprised when a "bad" lot is accepted andd makes it to the floor.

If you study AQL acceptance sampling curves, you might be surprised at how "loose" the common ones are from the customer standpoint.
 

johnnybegood

Involved In Discussions
#4
Does it matter which to use (AQL or LTPD) if I buy-off at in-coming or out-going inspection? I (the QA) buy-off at out-going visual inspection...when do I accept the lot, reject or sample again. Sometimes when there is high reject, Production is requested to performed 200% inspection before the product it brought to QA for buy-off. Question is in what situation it warrant a 200% inspection?
 
R

Rick Goodson

#5
johnnybegood,

In answer to your question of 'what situation warrants 200% inspection'. No situation warrants 200% inspection. You can not inspect quality into a batch of material. All you can do is cull out bad product. Typically to get to around 99% confidence you need to do 350% inspection. It just doesn't make sense.

Now, to the practical side of things. Sampling schemes only work if you apply the scheme not the plan. An AQL plan such as the old military MIL-STD-105 only worked if you used rectification and switching procedures. That is, the specific rejected lot was 100% inspected and the plan went to tightened or loosened inspection based on past results. The sampling scheme was set to control quality levels over time, not for a specific lot of material. As Dave S. said, AQL plans should generally be used as short term stop gap measures to control quality to some tolerable level while improvements aree made. If you need to use sampling plans/schemes, there are many to choose from. As Dave S. recommends, I also suggest you get a copy of Ed Schillings book on acceptance sampling. IMHO it is the bible on sampling. It is a rough read, pretty technical. If you want something a little easier as a starter try Dale Besterfield's book on Quality Control. He dose a pretty good job of giving an overview of sampling plans and the inherent risks associated with them.

Just to muck up the works a bit, you need to evaluate any plan based on its risks. You should review the Operating Characteristic Curve (OC), and the Average Outgoing Quality (AOQ) and Average Outgoing Quality Limit (AOQL) to determine if the risks are accepptable.

Bottom line, you are better off spending resources on fixing the process than improving the sampling scheme. Sampling costs money and does not improve the product.

Hope this helps.
 
J

Juan Dude

#6
Re: LTPD (Lot Tolerance Percent Defective) vs. AQL (Acceptable Quality Level) Definit

Bump in the hopes someone offers additional help on the subject.
 
Thread starter Similar threads Forum Replies Date
R How to determine LTPD (lot tolerance percent defective) or RQL Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
R LTPD (Lot Tolerance Percent Defective) Sampling Plan with %Defect Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
O LTPD (Lot Tolerance Percent Defective) Formula for Calculator Inspection, Prints (Drawings), Testing, Sampling and Related Topics 18
L AQL (Acceptable Quality Level) vs. LTPD (Lot Tolerance Percent Defective) AQL - Acceptable Quality Level 12
R Formula to tie together - Confidence/Reliability Level AQL? LTPD? Reliability Analysis - Predictions, Testing and Standards 3
D LTPD, Alpha and Beta for this plan. Inspection, Prints (Drawings), Testing, Sampling and Related Topics 12
M Interpreting MIL-PRF-19500 (Performance Spec, Semicon Dev) - What is LTPD of 20 - ??? Manufacturing and Related Processes 4
J Sample size definition in an Automotive SMT pilot lot run Misc. Quality Assurance and Business Systems Related Topics 1
Q LOT or Serial Number Symbol not used when the information is contained in the UDI? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 1
D Supplied Product on Control Plan - Lot ranging in 40,000 pcs per product FMEA and Control Plans 3
Z Do we still have to put UDI if we have DI and lot number seperately on our product ? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 4
K FDA Lot Code format requirements Other Medical Device and Orthopedic Related Topics 1
R Documenting Expiration Date Extension for a specific lot ISO 13485:2016 - Medical Device Quality Management Systems 12
S Lot assignment for secondary reference standard - Pharmaceuticals Manufacturing and Related Processes 0
N AS9100 8.5.1 j) - Lot splitting - any loopholes? AS9100, IAQG 9100, Nadcap and related Aerospace Standards and Requirements 11
S Is Lot Number required in addition to UDI serial number? Other Medical Device Regulations World-Wide 7
I Lot or Batch definition for IVDs Imported Legacy Blogs 0
N IVD Lot Numbers and Expiration Dates - 21 CFR 809.10 Other US Medical Device Regulations 3
J PMA Device - Lot # change in New ERP Software - What are the FDA Requirements 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 0
S Requirements relating to Serial Number and Lot Number Other US Medical Device Regulations 6
V 'Representative' Sample of the Lot for a Continuous Process Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
J Change in Lot Release Specifications - Definition of "Substantial Change" EU Medical Device Regulations 14
M Lot Numbers of Plastic Disposables in an LDT (laboratory developed test) ISO 13485:2016 - Medical Device Quality Management Systems 6
M How to Mathemetically Derive the AQL Tables given Lot Sizes AQL - Acceptable Quality Level 5
M Component Lot Number Traceability - Class I reusable and "resposable" Medical Devices ISO 13485:2016 - Medical Device Quality Management Systems 10
D Dual Lot Manufacturing requirements for Clinical Customers Manufacturing and Related Processes 3
R Why the FDA requests Lot Number in Testing Reports 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 7
E Is Design Transfer to Production be complete prior to Release of first production lot 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 2
G Validating a Process Based on Lot Release Criteria Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
U AQL, Lot Size vs Sampling Plans AQL - Acceptable Quality Level 8
Sam Lazzara Lot Release Testing versus Process Validation Studies Qualification and Validation (including 21 CFR Part 11) 9
V FDA regulatory requirement on the lot number convention for medical devices US Food and Drug Administration (FDA) 2
K Can I use ANSI/AQL for the Total Number of Containers for the entire Lot? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
H How to calculate the Lot Reject Rate Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
A How can a sample can give information about bad products in whole lot? Quality Manager and Management Related Issues 3
M Pipet tips of the same Lot Number have different expiration dates Quality Manager and Management Related Issues 6
L Regulatory Submittal During 3 Lot Sterilization Validation EU Medical Device Regulations 1
C Statistics equation to determine the number of samples in a lot Statistical Analysis Tools, Techniques and SPC 8
P Lot Acceptance Plan that specifies BS 6001 Double Sampling Plans, general inspection Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
K Class Ins CE Mark Labeling Requirements (particularly Lot or Batch symbol and number) EU Medical Device Regulations 7
N Switch to 100% inspection when lot fails sampling? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 9
G Calculating the Fraction Defective Confidence Interval for a Lot Statistical Analysis Tools, Techniques and SPC 2
S Samples for a Destructive Test included in a Lot Size? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
E How to determine the Lot Size for the OQ Sampling Plan Inspection, Prints (Drawings), Testing, Sampling and Related Topics 11
Ronen E Matrixx Initiatives Recalls One Lot of Zicam? Extreme Congestion Relief Other Medical Device and Orthopedic Related Topics 0
C Changing the Sample Size of a Lot Statistical Analysis Tools, Techniques and SPC 8
J Expanding the c = 0 Small Lot Squeglia Table Sampling Plan Inspection, Prints (Drawings), Testing, Sampling and Related Topics 12
R Sampling Plan for Wafer Inspection (Small Lot) Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
P Certificate of Free Sales (CFS) - Need to attach to each lot of exported product? Other Medical Device Regulations World-Wide 2
C What's the sampling plan I need to inspect for each lot? AQL - Acceptable Quality Level 7
Similar threads


















































Top Bottom