Application Development and Testing
We recommend that a user who is trained and experienced in safety applications develop the application program for the intended SIL 2 or SIL 3 system. The developer must follow good design practices:
- Use functional specifications, including flowcharts, timing diagrams, and sequence charts.
- Perform a review of safety task logic.
- Perform application validation.
As you develop your safety application, consider the following.
IMPORTANT:
- The programming application has been certified to clause 7.4.4 of IEC 61508-3 Edition 2 and can be used during the coding lifecycle of controller-based applications and also as an aide in the module test, integration test, and validation test lifecycle phases. As a result, no additional justification for its use during those lifecycle phases is required. If, however, other tools are used, either on their own or with the application, additional justification for those other tools are required. It is your responsibility to verify that other offline tools that are used during all lifecycle phases are selected as a coherent part of the software development activities.
- It is your responsibility to conduct an assessment to determine the level of reliance that is placed on the programming application and the potential failure mechanisms that can affect the executable software when the application is used in a manner other than what is specified in the product documentation.
- You must verify that all programming and configuration information that is entered into the programming application, and downloaded to the controller, meets the requirements for your application. See Confirm the Project.
- As required by the safety integrity level, the software or design representation must match the characteristics of the application.
- As required by the safety integrity level, the software or design representation must be compatible with the features that are supported in the programming application and controllers. It is your responsibility to verify that the desired software and design representation are supported in the application and controllers. For example, if the design is represented in a flowchart format, it is your responsibility to convert that design to a ladder diagram.
- Use of third-party, or internally developed, tools to generate logic automatically to import into the programming application for compilation and download to a controller requires assessment of its suitability at the point in the development cycle where it is selected.
Provide Feedback