When designing functionally safe motor-control applications, should you tackle functional safety compliance at the beginning, as an initial design requirement? Or should you treat functional safety as an add-on feature, incorporated into the final stages of your design?
Functional safety should be part of the initial design requirements – interwoven with the intended functionality of the motor drive. This isn’t the norm, because traditional system design workflows don’t approach safety compliance synergistically. But neglecting to consider how you need to meet safety integrity compliance at the outset can result in costly delays when introducing systems to market.
The onset of Industry 4.0 and the growth of vehicle electrification and connectivity require that we change our approach to functional safety compliance. Simply put, we now have more motor systems in more applications, and a high bar for complying with functional safety standards.
Bharat Rajaram
Systems Engineering Manager
Arm-Based Microcontrollers
1 Defining functional safety compliance | The goal of functional safety standards is to manage and mitigate systematic
faults while also being able to detect and prevent (or, at minimum, render
safe) random hardware failures when they occur. |
2 Two attributes of functional safety system design | Functional safety involves developing systems to deliver an intended
function and to meet a safety integrity level. |
3 The recommended approach to designing functionally safe motor-control and drive systems | System engineers designing functionally safe systems should approach
functional safety compliance at the outset of the design process – not as an
afterthought. |
The goal of functional safety standards such as International Electrotechnical Commission (IEC) 61508 and International Organization for Standardization (ISO) 26262 is to manage and mitigate systematic faults while also being able to detect and prevent (or, at minimum, render safe) random hardware failures when they occur.
The adoption of a rigorous development process with independent verification and validation can help manage for systematic faults.
It is possible to detect, prevent or render safe random hardware failures by:
The pairing of safety mechanisms with each situational hazard then helps designers meet quantitative metrics such as safe failure fraction (SFF) and probability of failures/hour (PFH) as required by IEC 61508. For example, a Safety Integrity Level (SIL) 2 system must have an SFF≥90% and a PFH of ≤1000 failures in time over 1 billion hours of operation.