Variable characteristic properties

Variable characteristics are measured as floating point numbers for parameters, such as width, weight, temperature, and hardness.

If you select a variable type characteristic, you need to provide the following additional information:

Data Grouping

• Grouped

• Individual

The grouping of data is based on the setting for normal sample size. If the normal sample size is 1, it indicates individual data. If the normal sample size is greater than 1, it indicates grouped data. If it is grouped data, then you can enter the minimum sample size and maximum sample size, where the minimum sample size must be 2 or greater.

Sample Size

• Normal Sample Size

  Used by the Sample Viewer Control for entering manual results. The edit results dialog displays the fields for entry. This is also used by the Sample Recording Object to record automatic data when maximum sample size is Null.

• Minimum Sample Size

  Used by the evaluation of control rules stored procedure. When there are several results for the characteristic, control rule violations are evaluated.

• Maximum Sample Size

  Used by the Sample Viewer Control as the maximum number of results that can be manually entered for a characteristic. This is also used by the Sample Recording Object for recording automatic data. The Sample Recording Object records up to the maximum sample size.

Moving Average Span

The number of individual results that are included in a single Moving Average point. The size is displayed in the Moving Average chart.

Note: The optional information for defining a variable type characteristic are: sample size, trend limits, standard error of regression, X Bar charts, and moving average charts.

Sigma Estimate

Specifies whether the estimated sigma used in control limit calculations and Cp/Cpk calculations use the within subgroup standard deviation or the tables to look for factors to multiply by the range.

Control Limit Source

You can obtain control limits in the following ways:

• Automatically calculate from data

  Allows MES to calculate the control limits. This enables the options to enter the following:

  • Samples for Control Limit: Specifies the number of samples that are to be included in the calculation. This parameter limits the number of samples used in the calculation of control limits and process statistics, as do the parameters Cut-off time (in days) and Number of samples to consider calculating process statistics. For more information, see Control the amount of data used in process statistics calculations.

  • Samples required before Control Limits are calculated: Specifies the minimum number of samples that must exist before applying the calculated control limits to evaluate rule violations.

• Compute from standard values

  Specifies standard mean and standard deviation values that are used to calculate control limits adjusted for sample size (standard mean +/- 3 * standard deviation / square root of sample size). Selecting this option makes the following parameters available:

  • Standard Mean (Center Line) includes x-bar, x-individual, and moving average.

  • Standard Mean Is Target, if selected, indicates that the target is used as the Center Line for the standard mean and the standard mean of the characteristic is not used.

  • Standard Deviation (Variability Measure) includes range, and sigma.

• Use preset values

  Includes center line and upper and lower control limit values for Xbar, Range Sigma, IX (Individual), IR (Individual Range), Moving Average, Moving Range, and Moving Sigma charts. Enables the user to set control limits for each chart through the Chart and its limits list. For each chart component, you must enter the lower control limit, center line, and upper control limit. Select the Use preset values option to enter values for all the chart types.