Attribute Defect Category Analysis
Keywords: attribute, analysis, priority, defect, AQL, sample, defect, category, ranking, control limit, alarm, subgroup, MF, LU, CD.
DataLyzer® Spectrum software platforms with B4 in the registration code have a special feature for in-depth Attribute characteristic analysis. This application note will explain category analysis and how to implement it within DataLyzer® Spectrum.
NOTE: this application note assumes you have prior knowledge of DataLyzer® Spectrum. For more information on basic topics, refer to the DataLyzer® Spectrum user’s manual.
This attribute analysis feature was implemented to allow attribute characteristics to be analyzed based on categories of defects in addition to total number of defects. For example, defects can be sorted by priority so a separate graph can be viewed for all critical defects, all major defects, and all minor defects.
Defects can also be sorted by process so users can see what department had the most total defects. For example, if a part must be extruded, machined, and painted, several errors can happen at each step of the process. Categories can be used to see how many errors happened in each step of the process.
To implement the extended attribute category analysis, select SETUP/DEFINE DEFECT CATEGORIES from the main DataLyzer® Spectrum screen. To add a defect category, press the “Add” button. A window will appear. Enter the name of the defect category in the window and press “OK”.
The category you created will appear in the “Define Defect Categories” window. Continue this procedure of adding categories until you are satisfied with your category selections and fill out the associated fields for each category.
Each defect category has an associated row of user-defined data that must be filled out before data entry. In the order column, enter the importance of the defect category. For example, the most important category should be rated with a “1”, and less important categories should have higher numbers.
In the “Limit” field, enter the maximum number of defects for each category allowed per subgroup entered. This includes all defects within the defect category. For example, if the “minor” category contains the defects “blistered”, “scratched”, and “discolored”, the total number of defects of blistered, scratched, and discolored combined must not exceed five defects. .
The “Acceptance Number” field allows users to track defects over a specific period rather than just one subgroup. In the “Sampling Plan Size”, enter the number of pieces you wish to track. In the “Acceptance Number” field, enter the number of defects allowed in the given sampling plan size. If any subgroup’s number of defects exceeds this limit, the subgroup will be considered out of specification and labeled as such on the Hub status screen. If a negative number is entered into a limit cell, it means no limit is in effect.
Notice that if the “Sampling Plan Size” is the same size as the subgroup size, the “Limit” field and “Acceptance Number” field may have the same values.
The “Combine” field gives the option of creating a category to hold a cumulative count of all previous categories combined. There are three possible settings for the “Combine” field. The default setting is an unchecked box. This means that no additional category will be displayed. If you click the box once, a checked box appears with the word “Only”. This setting displays the cumulative category only, and does not display the individual category. If you click the box again, a box appears with the word “Both”. This setting displays the cumulative category as well as the individual category.
In the “Combined Name” field, enter a title label to correspond with the combined categories. The combined name cannot exceed twelve characters. If the “Combine” field is left blank, the “Combined Name” field may be left empty as well.
How it works:
If no entries are made in the combined column, only the main defect categories appear in the defect category table below the attribute graph during data entry. They tally individually with a total defects option. You can see a graph for each category and the total by clicking the category button for each one.
In some cases you may wish to combine categories together and name the combination separately. In those cases, you can use options in the “Combine” column. These options include “Only” and “Both”. “Only” replaces the associated main category row with a row labeled from the “combined name” column in the table below the control chart. This row contains a cumulative tally of all rows above it. The main category it replaced will continue to be tallied behind the scenes. “Both” leaves the main defect category in the table and adds a row for the cumulative tally in the table.
The graphic below shows the setup for the category table that will appear below the control chart during data entry. When viewing control charts for an attribute, a separate count will be kept of critical defects, major defects, and minor defects. Since the “Only” setting is selected in the “Major” category, however, the “Major” category will not appear on the control chart, never the less an internal count for it will be maintained. The “Major” category will be replaced in the table by a cumulative tally of the rows above displaying the totals for “critical” and “major” defects. This row will be labeled “Important”, as designated in the “Combined Name” column.
Since “Both” appears in the “Combined” column for the “Minor” defects row, it causes both the minor defects and a cumulative row to be inserted. The cumulative row will be labeled “All Defects”. Example data entry and control chart windows for this example are shown later in this document.
Once you are satisfied with the changes you made to the “Define Defect Categories” window, press the “Ok” button to save your changes and exit to the main DataLyzer® Spectrum screen. Press the “Cancel” button to exit to the main DataLyzer® Spectrum screen without saving your changes. To delete a category, place the cursor in the row of the category you wish to delete and press the “Delete” button. Categories in use by a characteristic may not be deleted. To rename a characteristic, place the cursor in the row of the category you wish to rename and press the “Rename” button. A window similar to the “add category” will appear. Enter the name you want in this window and press “Ok’.
This is what the control chart looks like before entering data:
Attribute characteristics with defect categories should be created the same way as normal attribute characteristics. Once the attribute is created, press the “Use Categories” checkbox located in the middle right-hand area of the characteristic creation window. A new column named “Type” will appear in the defect definition area of the attribute window. In this column, use the drop down box for each defect to select a previously defined category for each defect. Press File/Save & Exit to save the changes you made.
Enter data for the extended attribute analysis in the usual manner of data entry. Notice that the defect category of each defect is listed next to its name. In the bottom of the control chart screen, there is a table showing how many defects were found in each subgroup by category. Pressing any of the category buttons to the left of the table will show the control chart for the given category instead of displaying the total number of defaults, which is the default. The title bar at the top of the data entry window will identify which category is being viewed.
This is how the window appears during data entry:
When creating the defect categories, specifications were set for number of defects allowed per Sampling Plan Size and Subgroup size. If either of these limits are exceeded, DataLyzer® Spectrum gives the operator an error message before saving the data values. The specific block for the subgroup out of control and defect category out of control is saved in the color red in the category table below the control chart graph. When using combined categories, if the subgroup limit or acceptance number is exceeded for the cumulative associated categories, the combined category box will be shown in red. When the subgroup limits are exceeded, DataLyzer® Spectrum interprets it as data entered out of specification limits. The point is saved in red on the control chart.
The following graph is an example of the total attribute count. It shows the total number of defects for all categories at once. To view the total attribute chart from a category’s chart, press the “all” button that is located below the minor column. To view the chart for any specific category, press the button in the lower left hand corner with the category’s name on it.
The following graph is a graph of the “critical” category. Notice that the only points shown are points shown in the “critical” category.
The following graph is an example of the “Minor” graph.
The following graph is an example of the “Important” combined Critical and Major categories graph.
The following graph is an example of the “All Defects” combined Critical, Major, and Minor categories graph.
DataLyzer® Spectrum Application Note
Compliments of DataLyzer International, Inc.