An accelerated life test was performed, and the results are in the Capacitor ALT.jmp sample data table (in the Design Experiment folder). Fifty units were tested at each of three temperatures (85o, 105o, and 125o Celsius) for 1500 hours. The resulting model is used to predict the probability of failure at 100,000 hours at normal use conditions of 25o.
1.
Open the Capacitor ALT.jmp data table in the Design Experiment folder.
2.
Run the Fit Life by X table script.
Distribution Profiler for Capacitor Model
The predicted probability of failure at 100,000 hours at 25o is 0.00358, with a confidence interval of 0.00056 to 0.0227. The analyst wants to decrease the width of the confidence interval. To do so, the experiment needs to be augmented with additional data.
1.
Select DOE > Accelerated Life Test Design.
2.
Select Design for one accelerating factor and click Continue.
3.
4.
Enter 5 for Number of Levels.
5.
Enter 25 for both Low Usage Condition and High Usage Condition.
6.
Click Continue.
7.
8.
Select Weibull for Distribution Choice.
9.
Under Prior Mean, enter the acceleration model parameters from the Fit Life by X Estimates report. See Fit Life by X Estimates.
Enter 1.389 for Temperature.
Fit Life by X Estimates
10.
Enter 100,000 for both boxes for Time range of interest.
11.
Enter 1500 for Length of Test.
12.
Enter 300 for Number of Units Under Test. The previous experiment used 150 units, and the next experiment uses 150 units, for a total of 300.
Completed Window
13.
Click Continue.
15.
From the red triangle menu for Accelerated Life Test Plan, select ALT Optimality Criterion > Make Probability I-Optimal Design.
16.
Click Make Design.
Optimal Design
184 units at 85o. Since the previous experiment used 50 units, 134 additional units are needed.
0 units at 95o. The next experiment will not utilize any units at this level.
50 units at 105o. Since the previous experiment already used 50 units, no additional units are needed.
0 units at 115o. The next experiment will not utilize any units at this level.
66 units at 125o. Since the previous experiment used 50 units, 16 additional units are needed.