You can compute required sample sizes for reliability tests and reliability demonstrations using the Reliability Test Plan and Reliability Demonstration features.
The Reliability Test Plan feature computes required sample sizes, censor times, or precision, for estimating failure times and failure probabilities.
To launch the Reliability Test Plan calculator, select DOE > Sample Size and Power, and then select Reliability Test Plan. Reliability Test Plan Window shows the Reliability Test Plan window.
Interval Ratio is sqrt(U/L), the square root of the ratio of the upper and lower limits.
Twosided Interval Absolute Width is UL, the difference of the upper and lower limits.
Lower Onesided Interval Absolute Width is TL, the true value minus the lower limit.
Twosided Interval Relative Width is (UL)/T, the difference between the upper and lower limits, divided by the true value.
Lower Onesided Interval Relative Width is (TL)/T, the difference between the true value and the lower limit, divided by the true value.
After the Continue button is clicked, two additional statistics are shown:
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2.

Select Reliability Test Plan.

3.

Select Weibull from the Distribution list.

6.

Select Twosided Interval Absolute Width from the Precision Measure list.

7.

Select Estimate time associated with specified failure probability.

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9.

Enter 2500 for Censor Time.

10.

Enter 200 for Precision.

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A reliability demonstration consists of testing a specified number of units for a specified period of time. If fewer than k units fail, you pass the demonstration, and conclude that the product reliability meets or exceeds a reliability standard.
The Reliability Demonstration feature computes required sample sizes and experimental runtimes for demonstrating that a product meets or exceeds a specified reliability standard.
To launch the Reliability Demonstration calculator, select DOE > Sample Size and Power, and then select Reliability Demonstration. Reliability Demonstration Window shows the Reliability Demonstration window.
is the assumed failure distribution. After selecting a distribution, specify the associated scale parameter in the text field under the Distribution menu.
A company wants to get the required sample size for assessing the reliability of a new product against an historical reliability standard of 90% survival after 1000 hours. From prior studies on similar products, it is believed that the failure distribution is Weibull, with a β parameter of 3. The company can afford to run the demonstration for 800 hours, and wants the experiment to result in no more than 2 failures.
1.

2.

Select Reliability Demonstration.

3.

Select Weibull from the Distribution list.

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Enter 2 for Max Failures Tolerated.

6.

Enter 1000 for Time.

7.

Enter 0.9 for Probability of Surviving.

8.

Enter 800 for Time of Demonstration.

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