The latest functional safety standard ISO 13849-1:2023 Safety of machinery - Safety-related parts of control systems - Part 1: General design principles, covers electromagnetic compatibility (EMI) aspects in functional safety.
In the previous version of ISO 13849-1:2015, such an aspect was mentioned in passing, without a defined methodology, relying more on good engineering practice. But the new version of the standard has changed all that and offers several methods to ensure compliance with electromagnetic compatibility requirements
Annex L offers four paths:
- Comply with the basic requirements of the product standard
- Comply with the requirements of standard IEC 61000-6-2:2016
- By implementing electromagnetic compatibility control measures at the system level (Table L.1)
- Comply with general EMI standards for functional safety, such as IEC 61000-6-7 or IEC 61326-3-1.
Looking at each path in detail:
A – Comply with the basic requirements of the product standard, such as IEC 61800-5-2, but it is not always possible and necessary. Sometimes it is not possible to apply the product standard to certain machinery, or it is not necessary to achieve such a high level of safety.
Path A allows reaching up to PL =e
B – Comply with standard IEC 61000-6-2:2016 Electromagnetic compatibility (EMC). Part 6-2: General standards. Immunity standard requirements for industrial environments. This path is the easiest, as it allows you to apply various basic design solutions to achieve compliance.
Path B only allows reaching PL =a
C – By implementing electromagnetic compatibility control measures at the system level (Table L.1). The control system is based on a point system, where points are awarded for each EMI safety solution implemented, for example, whether shielded cables are used, whether EMI filters are applied, etc. The solutions and points to be obtained are given in Table L.1.
One of the control measures is to carry out an EMI risk analysis of the system, an example of which is given in Table L.2, which lists possible sources of interference, their types, possible effects on the rest of the system and methods of prevention.
Path C allows reaching PL=d, with Cat 2, Cat 3 and Cat 4 systems, if at least 280 points out of a possible 390 are obtained. And with Cat B and Cat 1 systems you need to collect 230 points.
Path C allows reaching even PL=e, but only the 4 cat system, where all additional requirements are met.
D- Comply with general EMI standards for functional safety, such as IEC 61000-6-7 or IEC 61326-3-1. This path is based on the Common Electromagnetic Compatibility Immunity Standards for Functional Safety in Different Environments, which must be fully met by testing.
Conclusions
The latest version of the standard is a big step forward in terms of functional safety from an electromagnetic compatibility point of view. To ensure compliance, the standard allows both EMC testing and the implementation of certain security solutions, which can be evaluated with a flexible point system.
Testing the equipment in an EMC lab or on-site installation is the best solution to ensure up to PL =e, but to evaluate the disturbance immunity of the systems, a good test plan must be created, where the systems can be fully controlled and evaluated, so that the testing is fully reliable. For example, the emergency stop system should be tested both in the activated state and in the inactive state, changing the system states from time to time in order to observe any malfunction of the system that could affect safety.
Path C is the most suitable for large equipment, which is physically impossible to qualitatively test, in terms of fault resistance, therefore, using the established security solutions implementation with a point system, you can get an optimal result, up to the level of PL=d.
It is also possible to use this path at the initial stage of equipment development, already applying the solutions presented in it in the basic structure, thereby preventing possible inconsistencies in the future.
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