Settings for Control Chart Types
Control Chart Types
The control chart types are defined in the Customizing application as a two-level view. The first level is used for general settings for the control chart type. The second level is used for individual track settings.
Each control chart type has a three-character ID and is described by a short text in several languages. Ascending numbers from 900 onward and characters from A to Z are reserved as identifiers for customer enhancements for the predefined control charts.
General Control Chart Settings
The following general control chart settings are defined in Customizing:
The requirements that must be fulfilled by an inspection characteristic so that the control chart type can be used are stored for each control chart type. These include the following indicators for:
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Measured values-
Upper specification limit-
Lower specification limit-
Confirmation of number of defects-
Single result-
Independent multiple samples (or inspection points)-
Scope not fixed-
Fixed scope-
Smaller scope-
Larger scopeThe indicator for independent multiple samples defines whether individual sample records of an inspection characteristic are to be included in the control chart. These sample records can result from sampling procedures with independent multiple samples or inspection points. The indicator must match the sampling procedure exactly.
The other indicators simply define minimum requirements for the inspection characteristic. The tolerance or single results are not required for an `x-Shewhart chart for example. These indicators, therefore, are not set in the requirements profile. This control chart, however, can also be used for characteristics with a tolerance range limited on one side or on both sides or with single values.
This parameter defines how the x-axis of the control chart is displayed. The following four options are available:
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Object number (inspection lot, sample, inspection point)-
Creation time (of data record)-
Time of last change (to data record)-
Inspection timeThe reference axis is valid for all tracks in a control chart. The entries for reference axes with a time reference are not equidistant but refer to the actual time intervals. If all of the time values refer to the same day, a finer time grid is selected than if they are distributed over more than one day.
For reference axes with object numbers, you can also specify the number of samples to be displayed simultaneously in the graphic.
Entering the number range defines the number range from which the numbers for new control charts are taken. The number range 1 should be used if you do not want to differentiate between the control charts.
The name of a function module is stored for calling up the control chart. The QRKG_STANDARD_CHART module is entered in the standard system for all control charts. This module is used to display a one or two-track control chart with horizontal control limits. The control chart is created using the OCX Graphics function. If you want a graphical representation using the SAP Statistics Graphics function, select the Modal Graphics function.
If you want to modify the graphical representation or the functions available in the graphic, you can enter the name of a customer-specific module here. It is advisable to make a copy of the standard module for this purpose.
You can use the test call function to check whether the modification was successful. A simulation of the call function is then performed using example data; you do not have to create an inspection plan or inspection lots.
Information on the assigned function module is available using the system help functions.
Track Settings
A one-digit number is used to differentiate between the tracks of a control chart type. In theory, therefore, up to nine tracks can be defined for each chart. The standard system contains settings for one and two-track control charts. The track type is described by means of a short text in several languages.
The track is assigned a function module. The information for selecting or defining the control variable and the algorithms for calculating the control limits are programmed in this module.
The following modules are implemented in the standard system:
C-chart for the number of defects with sigma limits
EWMA chart with total dispersion
Acceptance chart for `x with internal dispersion
Acceptance chart for `x with total dispersion
Shewhart chart for `x with internal dispersion
Shewhart chart for `x with total dispersion
Shewhart chart for `x with dispersion over the moving range
Moving average chart with total dispersion
Moving range chart for sample size n = 1
NP chart for the number of nonconforming units with sigma limits
P chart for the number of nonconforming units with sigma limits
Shewhart chart for s with internal dispersion
Shewhart chart for s with total dispersion
U-chart for the number of defects for each sample unit with sigma limits
You can replace these modules with customer-specific modules if necessary.
The function modules have six possible parameters that can be set in the details screen for the track. In this way, you can influence the statistical levels when the control limits are calculated. The way in which the parameters are used can vary from module to module.
The action limits of an `x Shewhart chart can be calculated in such a way that 99% or 99.73% ( 3 s- rule) of the mean values are within the limits, if the process is not in control.