RPA | Reliability Prediction Analysis

Introduction

The reliability of a system is the probability that the system will operate successfully in a certain period of time. The RPA predicts the reliability of the system calculating its failure rate.

Note that the fatigue can be neglected since it is not a driver in the failure of an electronic component.

The unavailability of a component follows the equation:

\[Q=\int_0^t \lambda (t) e^{-\lambda (t) t} dt\]

Following the Constant Failure Rate per Hour model, the reliability probability (1-unavailability) can be expressed with the following formula:

\[R=Q-1=e^{-\lambda t}\]

Where:

• R: Probability that the system will operate without failure for t hours

• λ : Failure rate in hours-1

• t : Time in hours

The failure rate consists on how many times the system will fail per unit of time. In the common practice, the failure rate is given as failures per million hours.

The MTBF (Mean Time between Failures) is introduced considering it gives a practical value on the period a system will be functional until failure.

MTBF is directly related to the failure rate as indicated in the following formula:

\[MTBF=\frac{10^6}{\lambda}\]

MTBF: Mean Time Between Failures in hours λ: Failure Rate in (million hours)-1

To calculate the failure rate for a given system, it is necessary to sum the failure rate of all the components considering that the failure of a subsystem will drive to the failure of the assembly:

\[System Failure Rate = \sum_{i=1}^{n} Component Failure Rate_i\]

The failure rate of the basic electronic components are provided depending on the standard (e.g. MIL-HDBK-217F Notice 2 or HDBK-217Plus^TM).

Content

The content of the FTA module is:

• BOM: Bill Of Material
  • Actions
  • Import/Export BOM
• EPRP: Electronic Parts Reliability Prediction
  • FIDES 2009
• NPRP: Non-electronic Parts Reliability Prediction
• Settings

Default Parameters

Robin is aware of the difficulties that the engineer can find during early stages of the design where the system architecture is not clearly defined. For this reason, the EPRP: Electronic Parts Reliability Prediction and NPRP: Non-electronic Parts Reliability Prediction sections are provided with an option to use default parameters and obtain an estimation of the order of magnitude of an item failure rate. This option will not only be useful to understand which is the estimated reliability of the item in average operating conditions, but will also help the engineer to base their decision on reliability aspects.

Note

The option to use Set default parameter values is currently available for the following standards:

• MIL-HBDK-217F

• HDBK-217Plus^TM

• NSWC-11