Using a Threshold Parameter for a Data Set
For a parametric life data set that uses the Weibull (3 Parameter), Exponential, or Rayleigh distribution, you use the γ (gamma) value to specify a threshold parameter. For more information, see Threshold Parameter. The ALT module does not support the use of a threshold parameter.
1. In the LDA Navigator, select the parametric life data set that is to use a threshold parameter.
2. To specify the threshold parameter, do the following:
a. Select the Weibull Parameters window to make it active.
b. For Distribution, select Weibull, Exponential, or Rayleigh. Only these three distributions support a threshold parameter.
c. If Weibull is selected as the distribution, for Model, select 3 Parameters. If either of the other distributions is chosen, select 2 Parameters
Under Calculation results, the γ parameter is shown. The status for Fixed? determines whether it value is calculated or specified. By default, this checkbox is cleared so that the value is calculated.
d. Select Fixed? for the γ parameter. The field to its right becomes available.
e. In this field, enter the value to use. Auto-Calculate data sets in the System file properties controls whether the data set is calculated as you enter data and parameter values. For more information, see Data Set Calculations.
3. To generate and view the probability plot, do the following:
a. In the Weibull Plot Options pane, for Plot type, select Probably Plot.
b. If necessary, in the title bar, click Calculate to recalculate the data set.
c. In the Weibull Plot pane, view the probability plot. Lines are shown for both the real time domain and the threshold parameter shift.