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ALTA Tab

The ALTA tab is visible when you view an ALTA standard folio data sheet for accelerated life testing analysis.

Analysis

Calculate estimates the parameters of the chosen model, based on the current data set and the specified analysis settings.

Plot creates a new sheet in the folio that provides a choice of applicable plot types. For standard folios, this includes plots such as use level probability, reliability vs. time, life vs. stress, etc.

Quick Calculation Pad opens the Quick Calculation Pad, which allows you to calculate results, such as the mean life and the probability of failure, based on the currently active data sheet.

Distribution Wizard opens the Distribution Wizard, which helps you select the life distribution that will best fit your data.

3D Plot creates a 3D graph of the surface plot of the likelihood function. It plots the likelihood values (LK values) with respect to the estimated parameters of a distribution. The shape of the plot may help you to evaluate the amount of variability in the parameter estimates. A small surface (tall, tower-like peak) suggests that there is less uncertainty in the parameter estimates at the maximum LK value, while a large surface suggests that there is a large uncertainty in the parameter estimates.

In addition, the graph provides a choice of several functions that you can plot with respect to time and stress. This includes the pdf, failure rate, reliability and unreliability functions. The shape of the plot may help you to evaluate how the function is influenced by time and stress.

Folio Sheets

Insert Data Sheet inserts a new blank data sheet into the currently active folio and opens the ALTA Folio Data Sheet Setup window, which allows you to select what types of data to include in the new data sheet.

Insert Additional Plot inserts an overlay plot in the currently active folio. This allows you to display in a single plot results from multiple data sheets within the folio. This provides an easy visual method to compare analyses. For example, you may wish to show the reliability plots of two product designs in the same plot.

Insert General Spreadsheet inserts a new blank general spreadsheet into the currently active folio.

Select Sheet opens the Select Sheet window, which allows you to select which sheet in the current folio you want to be active.

Move or Copy Sheet opens the Move/Copy window, which allows you to move or copy any of the sheets within the currently active folio. Select the sheet that you wish to move and then click (move to end) to move the selected sheet to the end of all the sheets in the folio. Select Create a Copy to create a copy of the selected sheet.

Delete Sheet deletes the current sheet within the folio.

Options

Set Use Stress opens the Use Stress Level window, which allows you to define the use stress values for the selected stress type(s) in the current folio.

Select Stress Columns opens the Select Stress Columns window, which allows you to select which stress type(s) in the current folio to consider when calculating the parameters of the model (i.e, the life-stress relationship and distribution combination).

Alter Parameters

- Alter Parameters (w/o) Recalculation allows you to alter the values of the calculated parameters, assuming that the ranks, the likelihood function and the Fisher Matrix (evaluated at the original parameter estimates) remain the same. In plots, the position of the data points remain the same but the solution line and all subsequent analysis made via the QCP and other tools are based on the modified parameter values. Therefore, the analysis may be appropriate only within the context of your specific scenario.
- Alter One Parameter (and Recalculate) allows you to manually alter one of the parameter values and then have the software estimate the other parameter values that would result in a good fit for the distribution. The ranks and the likelihood function are assumed to remain the same; however, unlike the Alter Parameters (w/o) Recalculation method, the Fisher Matrix is evaluated at the altered parameter values. Therefore, the analysis may be appropriate only within the context of your specific scenario.

Stress Transformation opens the Stress Transformation window, which allows you to specify one transformation equation for each stress that will be used in the analysis.

Likelihood Ratio Test opens the Likelihood Ratio Test window, which allows you evaluate the discrepancy between the estimates of the shape parameter at the various accelerated stress levels. The test helps you to determine whether the units in the sample will fail in the same manner across different stress levels.

Convert Stress Values allows you to convert all the values entered in one of the stress columns to another value or to another stress unit (e.g., Celsius to Kelvin).

Format and View

Alter Data Type opens the ALTA Folio Data Sheet Setup window, which allows you to change the data entry columns in the current data sheet. Note that when you change the setup, you may lose information already entered in the data sheet. For example, switching the data sheet from one that supports interval data to one that supports only right censored data will remove all the inspection times.

Override Plot Color opens the Override Plot Color window, which allows you to ignore the default colors of the plotted line and points, and apply a color that you specify. This setting is activated in the source data sheet of the plot. This means that when you enable the setting for a particular data sheet, it applies only to the plots that you create for that data sheet and not the plots for all other data sheets that may be within the same folio. Note that only the colors of the lines and points are affected. Other settings such as the line style and thickness, or the point size and shape are based on the settings that you have specified in the Plot Items page of the Plot Setup window.

Set Headers as Default sets the column headers in the currently active data sheet as the default headers for all ALTA standard folio data sheets.

Restore Default Column Headers uses the default column headers for the columns of the currently active data sheet.

Add/Remove Columns allows you to add or remove stress columns or subset ID columns in the currently active data sheet.

Auto Group Data opens the Auto Group Data window, which allows you to group together data points with the same failure/suspension times. Grouping data significantly speeds up calculations when you have a very large data set.

Hide Control Panel allows you to hide the control panel in the current window.

Synthesis

Publish Model allows you to use the results of analysis (life-stress relationship and parameters) as a resource object and make it available for unlimited use anywhere within the project, in any Synthesis-enabled application that has a need for that type of object.