SPC Chart Maintenance

You use this activity to define control charts used for SPC analysis. These control charts are used to monitor the manufacturing processes and to help target the areas within the processes that can be improved. The control charts can contain any variable data. For more information, see Statistical Process Control (SPC).

Fields

The following tables describe fields requiring explanation:

Main Tab Page
Field	Description
Chart Type	The type of control chart for which you are adding or changing statistical chart information. The displayed chart type can be a variable data chart. Individual: Displays each value of the material being measured Median: Calculates and displays sample size medians. They are used when it is desirable to give little weight to occasional wild shot values. The median chart should be used only when subgroup sizes are small since the efficiency of the median in estimating the true universe mean decreases with increasing subgroup size. Moving Average: Calculates and displays the moving averages of subgroups Moving Range: Calculates and displays the moving range of subgroups Process Capability: Displays a normal curve superimposed over a histogram of data and several statistics Caution If you want to save a Process Capability chart, you must fill in the Upper Spec Limit, Target, and Lower Spec Limit fields. End of the caution. X-Bar and R: Displays the means and ranges of the subgroupsX-Bar chart calculates and displays sample size ranges X-Bar and S: Calculates and displays the means and standard deviations of the sample sizes. X-Bar chart calculates and displays sample size averages. S chart calculates and displays sample size standard deviations. Note that if you select X-Bar and R and X-Bar and S charts, the system enables all the fields on the Secondary Chart tab page.
Subgroup Size	The number of data points to be collected per plot point for this control chart. For Median charts, the entered number must be between `2` and `25`. For all other charts, the entered number must be between `2` and `30`.
Max Plot Points	The maximum number of plot points displayed on this control chart. A number between 2 and 100 is recommended.
Max Data Age (days)	The maximum age (in days) of the data points to be used in the analysis and the chart display Note that the value of this field depends on the number of plot points specified in the Max Plot Points field.
Propagate Alarms	If selected, allows the system to generate the alarm events if some point on chart is out of the limits defined in SPC Chart Maintenance.

Chart Labels Tab Page
Field	Description
X Tick Label	Defines the type of labeling to each subgroup along the X Axis. Sequential (1 to N): Displays the number that starts at 1, is incremented by 1, and ends at the period 'N' Time: Displays the time the data was entered Date: Displays the date the data was entered Date/Time: Displays the date and time the data was entered SFC: Displays the SFC number on which the data was collected
X Axis Label	The label displayed along the X-axis of the control chart Note that this field is disabled if you select either the X-Bar and R or X-Bar and S option on the Main tab page.
Scale	Determines whether the chart's Y-axis scale is linear or logarithmic

Primary Chart Details Tab Page
Field	Description
Control Limit Options	None: Control limits are not used. Fixed: Control limits are fixed as specified by the user. Calculated: Control limits are calculated from the process data and the sigma coefficient.
Sigma Coefficient	The number of sigma, or standard deviation units, used to calculate the upper and lower control limits
Trend Rules	The identifier of the function group that contains the list of the rules used to determine if a manufacturing process is in a state of statistical control. These rules are used during the SPC analysis.