Review and Update Specifications for ALT Plans

After you specify the accelerated life test design details, you continue to the design review steps.

Figure 23.6 ALT Candidate Runs and Choices 

Candidate Runs

Enter the minimum and maximum number of units allowed at each level of the acceleration factors. If you are augmenting a previous experiment, for each setting, include the number of units already run at each level in the Minimum Units column.

Diagnostic Choices

The choices available depend on the design optimality criteria. The design optimality criteria is found under the Accelerated Life Test Plan red triangle menu. For a D-optimal design there are no diagnostic choices.

Time range of interest

(Available only for a failure probability optimal design.) Specify the time interval over which you want to estimate the fraction of the population that is failing. Enter the lower value in the left box and the upper value in the right box. If you are interested in a specific time point, enter that value in both boxes.

Probability of interest

(Available only for a quantile estimate optimal design.) Specify the failure fraction for which you want an estimate of time. For example, if you want to estimate the time at which 10% of the units fail, then enter 0.10.

Design Choices

Specify values relating to the length of the test, inspection intervals, and the number of units being tested.

Monitoring Type

Select from continuous or interval monitoring.

Continuous Monitoring

Select for a design with exact failure times recorded. Failure times beyond the length of the test are right censored.

Monitoring at Intervals

Select for a design with units inspected for failures at intervals. Failure times are interval censored. Enter the number of inspections, the time of the first inspection, and the time between inspections. For inspection intervals that are irregular, you can change the inspection times later in the Design Choices section.

Total Number of units under test

The number of units in the experiment.

– If you are designing an initial experiment, enter the number of units that you plan to test.

– If you are augmenting a previous experiment, enter the number of units tested in the previous experiment plus the number of units for the next experiment.

Length of test

(Available only for Continuous Monitoring.) Specify the length of time during which units are on test. When you make the design table, record each unit’s failure time or whether it was right censored.

Inspection Times

(Available only for Monitoring at Intervals.) Specify the times at which inspections are conducted. When you make the design table, these times are used to construct Start Time and End Time columns. The number of units failing in each interval is recorded.