# reliability_test_planner¶

class reliability.Reliability_testing.reliability_test_planner(MTBF=None, number_of_failures=None, CI=None, test_duration=None, one_sided=True, time_terminated=True, print_results=True)

Solves for unknown test planner variables, given known variables. The Chi-squared distribution is used to find the lower confidence bound on MTBF for a given test duration, number of failures, and specified confidence interval. The equation for time-terminated tests is: MTBF = (2*test_duration)/(chisquared_inverse(CI, 2*number_of_failures+2)) The equation for failure-terminated tests is: MTBF = (2*test_duration)/(chisquared_inverse(CI, 2*number_of_failures)) This equation can be rearranged to solve for any of the 4 variables. For example, you may want to know how many failures you are allowed to have in a given test duration to achieve a particular MTBF. The user must specify any 3 out of the 4 variables (not including one_sided, print_results, or time_terminated) and the remaining variable will be calculated.

Inputs: MTBF - mean time between failures. This is the lower confidence bound on the MTBF. Units given in same units as the test_duration. number_of_failures - the number of failures recorded (or allowed) to achieve the MTBF. Must be an integer. test_duration - the amount of time on test required (or performed) to achieve the MTBF. May also be distance, rounds fires, cycles, etc. Units given in same units as MTBF. CI - the confidence interval at which the lower confidence bound on the MTBF is given. Must be between 0.5 and 1. For example, specify 0.95 for 95% confidence interval. print_results - True/False. Default is True. one_sided - True/False. Default is True. If set to False, the two sided confidence interval will be returned. time_terminated - True/False. Default is True. If set to False, the formula for the failure-terminated test will be used.

Outputs: If print_results is True, all the variables will be printed. An output object is also returned with the same values as the inputs and the remaining value also calculated.

Examples: reliability_test_planner(test_duration=19520,CI=0.8,number_of_failures=7)

Reliability Test Planner results for time-terminated test Solving for MTBF Test duration: 19520 MTBF (lower confidence bound): 1658.3248534993454 Number of failures: 7 Confidence interval (2 sided):0.8

output = reliability_test_planner(number_of_failures=6,test_duration=10000,CI=0.8, print_results=False) print(output.MTBF)

949.4807763260345