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ANSI/ASQ Z1.4 Acceptance Sampling Plans
Devised in 1942 at Bell Labs Later became MIL-STD-105E ISO-2859 ANSI/ASQ Z1.4 (The American National Standard Institute and American Society for Quality Control Z1.4) Wording & terminology changes Additional tables added 1
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ANSI/ASQ Z1.4 Intended to be used for a continuing series of lots, but may be designed for isolated lots. Standard provides for single, double, and multiple sampling plans. ANSI/ASQ Z1.4 is also provided for normal, tightened, or reduced inspection. Plan is specified by the AQL, and sample-size code. 2
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ANSI/ASQ Z1.4 Normal inspection is used at the start of inspection with changes being a function of recent quality history. (แผนนี้ใช้เมื่อเริ่มทำการสุ่มตรวจล็อต และสามารถเปลี่ยนการตรวจเป็นแบบแผนผ่อนปรน (Reduced inspection) หรือเข้มงวด(Tightened inspection) ซึ่งขึ้นอยู่ประวัติของคุณภาพของสินค้าที่ทำการตรวจ) Tightened inspection: Generally used when producer’s recent quality history has deteriorated. (ใช้เมื่อประวัติของคุณภาพของสินค้าแย่มาก) Reduced inspection: Used when the producer’s recent quality history has been exceptionally good. 3
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ANSI/ASQ Z1.4 4
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Sample Size Code Letters
Most commonly used 5
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Comparison of Inspection levels
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Example For a lot size of 2000, an AQL of 0.65%, and an inspection level of III, determine the single sampling plans for normal, tightened, and reduced inspection.
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ANSI/ASQ Z1.4 Normal, Tightened, and Reduced Inspection
Start with normal inspection Switching Procedures Normal to tightened Institute when 2 out of 5 consecutive lots not accepted on original inspection Tightened to normal Institute when 5 consecutive lots accepted If not, then discontinue inspection under this plan 24
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ANSI/ASQ Z1.4 Switching Procedures Normal to reduced
Institute when: (all of the following) Preceding 10 lots on normal inspection have been accepted Total nonconforming in preceding 10 samples is less than number identified in Table 10-5. Production is at a steady rate Reduced inspection is considered desirable by responsible authority 25
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ANSI/ASQ Z1.4 Switching Procedures Reduced to normal
Institute when: (any of the following) A lot is not accepted Sampling procedure terminates with neither acceptance or rejection criteria have been met Production is irregular or delayed Other conditions 26
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