BS ISO 7870-3:2020 pdf free
BS ISO 7870-3:2020 pdf free.Control charts Part 3: Acceptance control charts.
For the purposes of this document, the terms and definitions given in ISO 3534-1k Iso 3534-2 and the
following apply.
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3.1 acceptable process
process which is represented by a Shewhart control chart with a central line within the acceptable process zone
Note ito entry: Ideally, the average value X of such a control chart would beat the target value.
Note 2 to entry: The acceptable process zone is shown in Figure 1. Information on the Stewhart control chart can be found in ISO 7870-2.
4 Symbols and abbreviated terms
NOTE The lSO/lFC Directives makes it necessary to depart from common SPC usage in respect to the differentiation between abbreviated terms and symbols. An abbreviated term and its symbol can differ in appearance in two ways: by font and by layout. To distinguish between abbreviated terms and symbols, abbreviated terms are given in Anal upright and symbols in Times New Roman or Greek italics, as applicable. Whereas abbreviated terms can contain multiple letters, symbols consist only of a single letter. For example, the conventional abbreviation of acceptable process limit, APL, is valid but its symbol in equations becomes APL. The reason for this is to avoid misinterpretation of compound letters as an indication of multiplication.
4.1 Symbols
ACL acceptance control limits
A1 acceptable process level
L lower specification limit
n subgroup sample size
Po acceptable proportion nonconforming items
Pi rejectable proportion nonconforming items
Pa probability of acceptance
5 Description of acceptance control chart practice
In the pursuit of an acceptable product or service, there often is room for some latitude in the ability to centre a process around its target level. The contribution to overall variation of such location factors is additional to the inherent random variability of individual elements around a given process level. In most cases, some shifts in process level must be expected and can be tolerated. These shifts usually result from an assignable cause that cannot be eliminated because of engineering or economic considerations. They often enter the system at infrequent or irregular intervals, hut can rarely be treated as random components of variance.
There are several seemingly different approaches to treating these location factors contributing variation beyond that of inherent variability. At one extreme is the approach in which all variability that results in deviations from the target value must be minimized. Supporters of such an approach seek to improve the capability to maintain a process within tighter tolerance limits so that there is greater potential for process or product quality improvement.
At the other extreme is the approach that if a high level of process capability has been achieved, it is not only uneconomic and wasteful of resources, but it can also be counterproductive to try to improve the capability of the process. This often is the result of the introduction of pressures which encourage “tampering with the process (over-control) by people qualified to work on control aspects but not product or process quality improvement programmes.BS ISO 7870-3 pdf free download.
