ISO 7870-5:2014

INTERNATIONAL ISO
STANDARD 7870-5
First edition
2014-01-15
Control charts —
Part 5:
Specialized control charts
Cartes de contrôle —
Partie 5: Cartes de contrôle particulières
Reference number
©
ISO 2014
© ISO 2014
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Published in Switzerland
ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 4
4.1 Symbols . 4
4.2 Abbreviated terms . 5
5 Specialized control charts . 5
6 Moving average and moving range control charts . 5
6.1 Control limits . 6
6.2 Interpretation . 6
6.3 Advantages . 6
6.4 Limitations . 6
6.5 Example . 6
7 z- chart. 9
7.1 Control limits . 9
7.2 Advantages .10
7.3 Limitations .10
7.4 Example .10
8 Group control chart .10
8.1 Control limits .12
8.2 Advantages .12
8.3 Limitations .13
8.4 Example .13
9 High-low control chart .16
9.1 Control limits .16
9.2 Interpretation .17
9.3 Advantages .17
9.4 Limitations .17
9.5 Example .17
10 Trend control chart .19
10.1 Control limits .20
10.2 Advantages .20
10.3 Limitations .21
10.4 Example .21
11 Control chart for coefficient of variation .24
11.1 Control limits .24
11.2 Advantage .24
11.3 Limitation .24
11.4 Example .25
12 Control chart for non-normal data .26
12.1 Control limits .27
12.2 Example .28
13 Standardized p- chart .32
13.1 Control limits .34
13.2 Advantages and limitations .34
13.3 Example .34
Foreword
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The committee responsible for this document is ISO/TC 69, Applications of statistical methods,
Subcommittee SC 4, Applications of statistical methods in process management.
ISO 7870 consists of the following parts, under the general title Control charts:
— Part 1: General guidelines
— Part 2: Shewhart control charts
— Part 3: Acceptance control charts
— Part 4: Cumulative sum control charts
— Part 5: Specialized control charts
— Part 6: EWMA control charts
iv © ISO 2014 – All rights reserved

Introduction
The Shewhart control charts as given in ISO 7870-2 aid in detection of unnatural patterns of variations
in data from repetitive processes and provide criteria for detecting a lack of statistical control.
However, there may be several special situations for variables data where Shewhart control charts
may be inadequate, insufficient or less efficient in detecting the unnatural patterns of variation of the
process, particularly where:
a) it takes considerable time to produce an item and as such sample results are available at large
intervals;
b) there are several subgroup sources that have approximately the same production rate, process
average and process capability;
c) process average is changing systematically;
d) sample size is large and sequence of production is irrelevant;
e) process does not have a constant target value.
In such situations, specialized control charts are to be used.
Similarly, special situations may be encountered in dealing with attributes data. There may be situations
when criticality of an incidence in a subgroup (nonconformity) is a matter of concern, but different
nonconformities are having different criticality. As such, all types of nonconformities cannot be treated
alike. Depending upon criticality, different ratings (weights) are required to be given to each class of
nonconformity, and accordingly demerit scores are calculated. Th
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