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When you select the ARINC allocation model in the Allocation utility, you must enter the following information on the control panel:
The Reliability Goal is the overall desired reliability for the system, expressed as a decimal from 0 to 1, excluding 0.
The Operating Time is the length of time the system will operate, in hours.
In addition, the Elements field will be update automatically to display the number of blocks that you have selected to include in the analysis (i.e., the number of check boxes that are selected in the Include column of the table).
Once you have entered all required information and clicked the Calculate icon, the following information will be displayed in the table for each block selected to be included in the analysis:
Present Failure Rate displays the block's failure rate that will be used in the allocation analysis. If you have selected the Use failure rate from current prediction check box in the control panel, the application will automatically populate this column based on the current prediction and it will be the same as the Current Failure Rate value. If you clear the check box, you can enter values for the blocks you have selected to include in the analysis.
Allocated Failure Rate displays the recommended failure rate for the block, based on the allocation analysis. This calculated result is expressed in failures per million hours (FPMH) for MIL-217 and NSWC, and in failures per billion hours (FITS) for Bellcore/Telcordia and FIDES.
Allocated MTBF (hrs) displays the recommended mean time between failures for the block, based on the allocation analysis. This calculated result is always expressed in hours.
Current Failure Rate displays the current failure rate for the block based on the current reliability prediction so you can compare with the recommended value.
Description:
Developed by ARINC Research Corporation, a subsidiary of Aeronautical Radio, Inc.
Assumes all subsystems are in series and have constant failure rates.
Allocates improved subsystem failure rates based on weighing factors, derived from the present allocation of the subsystem, that satisfy the expression:
where:
n = Number of subsystems.
λi = Failure rate allocated to subsystem i.
λ = Required system failure rate.
The steps are as follows:
Determine the present system failure rate.
Compute a weighting factor for each subsystem using the expression:
Allocate the new subsystem failure rates using the expression
where λ can be obtained by:
where:
R(t) = Reliability goal.
t = Operating time.
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