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
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
ANSI/ASQ Z1.4
 Normal inspection is used at the start of inspection with
changes being a function of recent quality history. (แผนนี้ใช้เมื่อ
เริ่ มทำกำรสุ่ มตรวจล็อต และสำมำรถเปลี่ยนกำรตรวจเป็ นแบบแผนผ่อนปรน (Reduced
inspection) หรื อเข้มงวด(Tightened inspection) ซึ่ งขึ้นอยูป่ ระวัติของคุณภำพ
ของสิ นค้ำที่ทำกำรตรวจ)
 Tightened inspection:
 Generally used when producer’s recent quality history
has deteriorated. (ใช้เมื่อประวัติของคุณภำพของสิ นค้ำแย่มำก)
 Reduced inspection:
 Used when the producer’s recent quality history has been
exceptionally good.
3
ANSI/ASQ Z1.4
4
Sample Size Code Letters
Most commonly
used
5
Comparison of Inspection levels
100
95
= 0.05
Percent of Lots Accepted (100Pa)
80
60
I = 1/2 n
II = n
III = 2n
40
III
II
I
20
100=10
0
2
4
6
Percent Nonconforming (100Pa)
8
10
6
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.
7
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
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8
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
9
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
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10