What is the difference between ISO 13849-1 and ISO 13849-2? And what is the purpose of ISO 13849-2? In this article we introduce the main aspects of ISO 13849-2 in regards to the Performance Level of safety-related control systems and to the validation process.
ISO 13849 for Performance Level verification and validation
The ISO 13849 standard is composed of two sections:
- The first part of the standard, ISO 13849-1, is well-known in the safety field. It concerns the design of the SRP / Cs, and provides the manufacturer with the requirements necessary to be able to design and build a safe SRP / Cs. The standard refers to the risk assessment to be conducted on the machine and to the reliability level (PLr) required for its safety-related functions.
- The second part of the standard, ISO 13849-2, is subsequent, since it refers to the validation of the SRP / Cs, and therefore, to those activities, such as checks, analyzes, and tests aiming at validating the SRP / Cs.
The second parte of the standard is actually less known and partially “underestimated” than ISO 13849-1. Performance Level calculaton usually stops at its verification, even though validation is the real added-value process for a manufacturer. The validation process of an SRP / Cs helps identify potential issues to be avoid during the mounting or the programming of the PLC.
Therefore, the purpose of the ISO 13849-2 standard is:
- To confirm that the SRP / Cs complies with the specific safety requirements established by the risk assessment
- To demonstrate that the SRP / Cs meets all the prescribed requirements, such as those related to architectural principles, diagnostics, system behavior in case of common failure or in case of systematic failure, etc.
The standard also indicates that the Performance Level Validation should be performed by someone independent from the designer / manufacturer of the machine.
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Phases of the validation of the Performance Level according to ISO 13849-2
Validation is an iterative process, which results in the validation of the product. For this purpose, there are three fundamental tasks to be carried out:
- The definition of a Validation Plan, containing all the pertinent and necessary documentation for validation. The Validation Plan describes all the phases and activities to be carried out. This consists of three fundamental phases: validation analysis, validation tests, and any other testing of the failure conditions, as required for the categories from 2 to 4.
- Once the Validation Plan is done, the next phase concerns the validation analysis, which is a documented detailed analysis referring to all the applicable standard requirements. This is the only mandatory phase according to the ISO 13849 standard.
- Finally, if required, the next phase is the execution of the functional tests. These are not mandatory according to the ISO 13849 standard, except for categories from 2 to 4. Categories from 2 to 4 are those that base the reliability on redundancy and fault tolerance, and for which the execution of tests on fault conditions is required.