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Software Used: Software Used: ALTA PRO
Download Example File for Version 10 (*.rsgz10) or Version 9 (*.rsr9)
Discrete data are also referred to as success/failure data or attribute data. These data sets consist of data from a test where a unit is tested with only two possible outcomes: success or failure.
The Grouped per Configuration data type is used when multiple units are tested and the number of units that fail are recorded for each configuration. Each stage of testing represents a unique configuration. Improvements are made to the system after all of the units within a given stage have been tested.
A one-shot system under development underwent reliability growth testing for a total of 68 trials. Corrective actions were incorporated after the 14th, 33rd and 48th trials. The configuration was not changed from trial 49 to 68. The trials and failures for each configuration are shown next, with cumulative values in bold.
The reliability of the final configuration is calculated in this example using the Crow-AMSAA (NHPP) model. The goal is to determine the reliability achieved by Configuration 4.
A standard folio data sheet configured for the Grouped Failure Times data type is created by selecting Discrete Data > Grouped per Configuration in the RGA Folio Data Sheet Setup window, as shown next.
Figure 1: Selecting the data type for the new folio.
The data set is then entered and the Crow-AMSAA (NHPP) model is selected for analysis, as shown next. The cumulative number of trials and failures for each state are entered.
Figure 2: Data set entered in the standard folio.
On the Analysis tab of the standard folio’s control panel, notice that Maximum Likelihood is selected for the analysis type. This is the only option available for this data type and model. In the Other Options area, it is specified that the data input is cumulative.
Figure 3: Analysis settings showing that the data are cumulative values.
After analyzing the data, a summary of results on the control panel shows the parameters of the fitted model.
A plot of the reliability vs. time is created. Each horizontal line represents the reliability at the given test stage (i.e., configuration).
Figure 4: Reliability vs. time plot showing the increase in reliability with each configuration.
You can see from the plot that the reliability for Configuration 4 is about 80%. However, an exact calculation can be obtained from the Quick Calculation Pad.
Figure 5: QCP showing the estimated reliability of the system at the fourth stage of testing.
The reliability of Configuration 4 is 0.8096 or 80.96%.1
