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| Reliability HotWire | |
| Tool Tips | |
 What
do the parameters B and C represent in ALTA?
The parameters B and C are used by ALTA for the Arrhenius and temperature-non-thermal life-stress relationships. The application returns values for these variables along with the shape parameter for the selected distribution (beta for Weibull or standard deviation for lognormal). However, it is much more difficult to glean information about the test items from the B and C parameters than from the shape parameter. Essentially, B and C are just variables for which ALTA solves in order to determine the relationship between stress and life; it is difficult to draw any conclusions about the behavior of the products based on the values of these parameters. However, you can get an indication of the nature of the relationship between life and stress from the parameter B. The sign of the B parameter indicates in which direction the life-stress relationship lies. If B is positive, the life of the product decreases with increasing stress. If B is negative, the life of the product increases with increasing stress (an unusual but by no means impossible situation). Similarly, the magnitude of the B parameter can indicate how quickly the life of the product changes with stress; values with larger magnitudes indicate that the life of the product is more sensitive to the stress. However, all of this is relative and one cannot draw any conclusions based on the value of B alone. The parameter C does not impart any useful information at all, it is merely a variable that ALTA solves for in order to complete the analysis.
A new block, with the same style and properties as the selected block, will be created in the diagram. The new block will be placed to the right of the original block and connected with a relationship line. How
can I show information from more than one data set on one plot in
Weibull++? Weibull++ Folios that contain more than one data set can easily display data from multiple sources using the Multiple Plot Sheet feature. Once the data sets of interest have been entered and analyzed, you can insert a Multiple Plot Sheet by making a selection from the Folio menu, pressing the hotkey combination Ctrl+M, or clicking the Multiple Plot Sheet icon in the toolbar.
Once the Multiple Plot Sheet has been inserted, you must select which data sets you want to appear on the multiple plot. The control panel on the right side of the Multiple Plot Sheet allows the user to choose the plot type, and shows which data sets have been chosen and are available for display. In order to include a data set for display in the multiple plot, double-click the desired data set in the Available Data Source(s) area. Notice that the distribution used to calculate the parameters for each data set is displayed in brackets (e.g. [W] indicates that the data set was calculated with the Weibull distribution.)
If a desired data set does not appear in the Available Data Source(s) area, it is usually for one of two reasons: 1) the desired data set has not been analyzed, i.e. the data have been entered but the parameters have not been calculated, or 2) the data set was calculated with a different distribution than the selected probability plot type. For example, if you have a data set that has been analyzed using the lognormal distribution, it cannot be displayed on a Weibull probability plot. This is because probability plots are constructed specifically for one type of distribution. If you want to display data from data sets analyzed using different distributions, a plot type other than a probability plot (e.g. reliability vs. time) must be used.
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