One Company | Four Decades Experience

The reliability prediction can begin at the outset of the design of a new product as soon as an estimate of component count can be made as the system and/or equipment failure rate is estimated as a function of the number of parts and quality in several part classes.  It involves generating reliability block diagrams, counting the number of parts in each assembly, and applying a generic failure rate and quality factor to those parts in compliance with the operational temperature and environment, in order to determine the overall system/equipment failure rate.

Benefits of the Parts Count Method

1) Rapid estimates of reliability that allows quick decisions on the feasibility of a design.

2) Parts Count Technique is applied early in the design phase to determine that the predicted reliability is acceptable to the reliability requirements.

3) Can be used to determine the optimum component procurement levels and provide the basis for determining spares requirements.

4) To assess progress in meeting design goals and evaluate environmental concerns.

5) Aiding in business decisions such as budget allocation and scheduling.

When the product has been designed and component stresses can be measured or calculated then a more accurate ‘parts stress’ reliability prediction can be made.  The system/equipment failure rate is therefore determined by considering the part type, part failure rate, part quality, operational stress levels (both electrical and thermal) and the derating characteristics applied to each part.

Benefits of the Parts Stress Method

1) Over-stressed parts and marginal stress levels in the design can be identified.

2) Thermal evaluation helps to ensure adequate heat dissipation.

3) Provides reliability estimates with a higher degree of confidence than Parts Count Method.

The objective of the Failure Modes Effects and Criticality Analysis (FMECA) is to identify design weaknesses, dormant failures, and potential catastrophic and critical failure mechanisms within a system or equipment and determine their probability of occurrence so that susceptibility to their associated failure effects can be eliminated from the design and/or reduced to an acceptable level.

Benefits of the FMECA

1) The identification of failures which, when they occur alone, have unacceptable or significant effects and to determine the failure modes which may seriously affect the expected or required product operation. 

2) The identification of items that are reliability sensitive and therefore provide an objective basis for deciding priorities for corrective design action.

3) The identification of potential failures that can be ranked according to their category of failure effect and probability of occurrence. 

4) Improve product/process reliability and quality thereby increasing customer satisfaction and relationships. 

5) Aids in the objective evaluation of design requirements and alternatives and assists in the identification of single point failures, their severity, and documents risk and the actions required to mitigate that risk.

6) To provide information for the selection of preventive or corrective maintenance points, the development of troubleshooting guides, built-in test equipment, and suitable test points.

7) Provides an open issue format for recommending and tracking risk-reducing actions. 

8) To facilitate or support the determination of test criteria, test plans, and diagnostic procedures.

9) To support the design of fault isolation sequences and plans for alternative modes of operation and reconfiguration.

10) Assurance there is adequate fault coverage of hardware failures through hardware, software, and/or firmware.

The Safety/Hazard Analysis is a process that includes the evaluation and verification of potential hazards that may be inherent within a system/equipment design. This process provides the methodology to evaluate the features of the hardware, software, and system design to ensure that all associated hazards including procedural controls and precautions have been correctly addressed. The data obtained from the completion of the Hazard Analyses allows for a full and complete risk assessment to be performed, to determine the level of risk associated with any given hazard based on the hazard severity and its probability of occurrence. 

Benefits of the Safety/Hazard Analysis

1) The review and analysis of the safety characteristics of the design both qualitatively and quantitatively, to determine where the emphasis has to be placed in order to eliminate potentially hazardous conditions.

2) To identify any safety-critical areas within the design.

3) The elimination and control of potential hazards through good design according to safety criteria and principles.

4) The identification and evaluation of materials used within the design that may be potential hazards.

5) The performance of a Risk Assessment to evaluate the risks associated to each hazard leading to risk reduction.

6) To establish operating precautions and controls necessary to ensure the safety of equipment and personnel during operation, handling, storage, transportation, and disposal.