Improving Industrial Functional Safety Compliance with High Performance Supervisory Circuits: Safety Critical Features-Part 3

Part 1 of this series demonstrated how diagnostics act as the backbone of functional safety (FS) compliance.

- Bryan Angelo Borres Sr Product Applications Engineer Analog Devices

Introduction

It highlights how supervisory circuits acting as diagnostic functions in a safety related-system (SRS) improve FS compliance through the three key requirements—systematic capability, reliability prediction, and architectural constraints. Systematic capability evaluates the effectiveness of quality management throughout the entire lifecycle of a product or service, from conceptualization to decommissioning. It emphasizes the goal of using a rigorous development process to avoid the introduction of systematic failures as well as the need for diagnostics to control such failures. Reliability predictions, on the other hand, indicate how likely the SRS is to fail with respect to time. Then, architectural constraints demonstrate the trade-off between the hardware fault tolerance (HFT), the ability to tolerate failures and safe failure fraction (SFF), or the tendency of the safety function to fail in a safe state—to which diagnostics are also mainly part of.

Part 2 of this series then introduced a way to improve SRS designs using FS-compliant diagnostic functions. Several advantages were noted, including:

1. Having their own failure mode, effects, and diagnostics analysis (FMEDA).

2. Having integrated safety features scoping several diagnostic functions.

3. Having their own diagnostics to detect on-chip random hardware failures.

4. Being future-proof against IEC 61508's upcoming revision.

5. Considering other countries' safety standards and directives.

6. Easing FS assessment.