How can you design reliable systems from the outset?

Reliable systems are essential for many domains, such as aerospace, healthcare, energy, and security. They deliver consistent performance, reduce errors and failures, and enhance user satisfaction and safety. But how can you design reliable systems from the outset, without relying on extensive testing and debugging later on? In this article, you will learn some key principles and methods of reliability engineering, a discipline that focuses on ensuring the dependability of systems throughout their life cycle.

1 Define reliability requirements

The first step in designing reliable systems is to define what reliability means for your system and its stakeholders. Reliability requirements specify the desired level and quality of service that the system should provide under normal and abnormal conditions. They may include metrics such as availability, reliability, maintainability, and safety. You should also consider the trade-offs between reliability and other factors, such as cost, performance, and complexity. Reliability requirements should be clear, measurable, and aligned with the system's objectives and constraints.

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Ahmed Abou Gharam, PhD

Global Engineering Leader | Driving Product Reliability & Testing Excellence in Automotive Electronics
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The definition of reliability is for a product to work as intended and perform its function without interruptions for a specific time. This applies to hardware, software, and people too (i.e. reliable person at work who is always on time). The requirements of reliability are user perception and how they intend to use the product. Therefore, a reliability engineer needs to understand the mission profile or duty cycle to gather user needs. For example, when buying a laptop computer for a general user who likes to work from different places, their reliability requirements would be long battery life. On the other hand, a video gamer would not care about battery life but care more about overheating and fast response.

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2 Apply reliability analysis techniques

The next step is to apply reliability analysis techniques to evaluate the system's behavior and identify potential failure modes, causes, and effects. These techniques can be qualitative or quantitative, depending on the level of detail and accuracy needed. Fault tree analysis (FTA) is a graphical method that shows how different faults can lead to a system failure. Failure mode and effects analysis (FMEA) is a systematic method that lists the possible failure modes of each component and their effects on the system and its functions. Reliability block diagrams (RBD) are graphical methods that show how different components are connected and how their reliability affects the system's reliability. Markov chain analysis (MCA) is a mathematical method that models the system's transitions between different states and their probabilities.

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Ahmed Abou Gharam, PhD

Global Engineering Leader | Driving Product Reliability & Testing Excellence in Automotive Electronics
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Reliability analysis consists of statistical evaluations of the product (i.e. hardware/Software) function over time. Essentially calculates the failure rate and how it compares to the reliability requirements or needs of the consumer. One of the commonly used tools for reliability analysis is Weibull analysis. It provides insight into the probability of failure at a given time.

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3 Design for reliability

The third step is to design for reliability, which involves incorporating reliability principles and best practices into the system's architecture, design, and implementation. This is done to prevent or reduce the chances of failure, complexity, and uncertainty, while increasing robustness and resilience. Examples of design for reliability include redundancy – adding extra components or functions to take over if the primary ones fail; modularity – dividing the system into smaller and independent units that can be easily replaced or repaired; diversity – using different types of components or functions that can perform the same task in different ways; fault tolerance – enabling the system to continue operating even if some components or functions fail; and fault prevention – eliminating or reducing the sources of faults, such as defects, errors, or environmental stresses.

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Ahmed Abou Gharam, PhD

Global Engineering Leader | Driving Product Reliability & Testing Excellence in Automotive Electronics
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Design for reliability is a process and a mindset of detecting and mitigating failure modes of a design before placing it in the field. There are many design for reliability tools, the type of tool depends on the design stage you are in in the development cycle. For example, in early phases, reliability engineers depend on simulation and virtual tools or prior history from similar products to assess risk and possible failure modes. In the middle stages, we use physical testing to verify our hypothesis. In the later stages, we monitor products in the fields for field failures and lessons learned for future revisions.

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4 Implement reliability testing and verification

The fourth step is to implement reliability testing and verification, which involves checking that the system meets the reliability requirements and performs as expected under various conditions. This can be done at various stages of the system's development, such as during prototyping, integration, validation, and deployment. Examples of reliability testing and verification include the Reliability Demonstration Test (RDT) to show that the system achieves a certain level of reliability with a specified confidence level; Accelerated Life Test (ALT) to expose the system to higher than normal stresses to induce failures and estimate its life span; Highly Accelerated Life Test (HALT) to expose the system to extreme stresses to identify its weak points and improve its design; and Reliability Growth Test (RGT) to monitor the system's reliability improvement over time as failures are detected and corrected.

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5 Manage reliability throughout the system's life cycle

The final step to managing reliability throughout the system's life cycle is ensuring that it maintains or improves its reliability as it evolves and operates. This includes planning, monitoring, controlling, and improving the system's reliability activities and performance. To do this, you should create a reliability plan that outlines the objectives, requirements, methods, and resources for development and operation. Additionally, you should collect and analyze reliability data such as failure rates, causes, and effects. Finally, use the data to identify and implement improvement actions like design changes or training programs. By following these steps, you can design reliable systems from the outset and ensure their dependability throughout their life cycle. Reliability engineering is a critical skill for any systems engineer looking to create systems that satisfy user needs and expectations.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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How can you design reliable systems from the outset?

1

2

3

4

5

6

1 Define reliability requirements

2 Apply reliability analysis techniques

3 Design for reliability

4 Implement reliability testing and verification

5 Manage reliability throughout the system's life cycle

6 Here’s what else to consider

Systems Engineering

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How can you design reliable systems from the outset?

1

2

3

4

5

6

1 Define reliability requirements

2 Apply reliability analysis techniques

3 Design for reliability

4 Implement reliability testing and verification

5 Manage reliability throughout the system's life cycle

6 Here’s what else to consider

Systems Engineering

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