What is the best way to approach control logic testing for safety-critical systems?

1 Define the scope

The first step in control logic testing is to define the scope of the test, which includes the objectives, requirements, assumptions, constraints, and criteria for the system under test. The scope should be clear, consistent, and traceable to the design specifications and the safety analysis. The scope should also specify the level of testing, such as unit, integration, or system testing, and the test environment, such as simulation, hardware-in-the-loop, or field testing.

2 Design the test cases

The next step is to design the test cases, which are the scenarios and inputs that will be used to exercise the control logic and observe the outputs. The test cases should cover all the relevant aspects of the control logic, such as functionality, performance, robustness, and fault tolerance. The test cases should also be representative, realistic, and diverse, to ensure that they capture the expected and unexpected behaviors of the system. The test cases should be documented and reviewed for completeness, accuracy, and validity.

3 Execute the test cases

The third step is to execute the test cases, which involves applying the inputs to the system and measuring the outputs. The execution should follow a predefined procedure and schedule, and use appropriate tools and equipment. The execution should also record and store the test data and results, such as timestamps, signals, values, and events. The execution should be conducted by qualified and authorized personnel, and follow the safety and ethical guidelines.

4 Analyze the test results

The fourth step is to analyze the test results, which involves comparing the outputs with the expected outcomes and evaluating the performance and compliance of the control logic. The analysis should use quantitative and qualitative methods, such as statistics, graphs, tables, and charts. The analysis should also identify and explain any discrepancies, anomalies, or failures in the test results, and determine their root causes and impacts. The analysis should be documented and reported for transparency and accountability.

5 Validate the test results

The fifth step is to validate the test results, which involves verifying that the test results are reliable, accurate, and consistent. The validation should use independent and objective sources, such as peer reviews, audits, inspections, or external evaluations. The validation should also check for any errors, biases, or uncertainties in the test results, and estimate their margins and confidence levels. The validation should be documented and communicated for feedback and improvement.

6 Improve the control logic

The final step is to improve the control logic, which involves applying the lessons learned from the test results to enhance the quality and safety of the system. The improvement should address any issues, defects, or gaps in the control logic, and implement any changes, corrections, or enhancements. The improvement should also retest the control logic to confirm that the changes are effective and do not introduce new problems. The improvement should be documented and tracked for traceability and verification.