What is Functional Safety? (Part 2)

Tech blog for beginner

In Part 1 article, we talked about ensuring the safety function even when faults exist in a system, that is Functional Safety. In this article, I will introduce the basic concepts of how Functional Safety (hereinafter referred to as FuSa) achieves this type of function.

Causes of failure

First of all, let’s understand the causes of failure. According to IEC-61508, the basic FuSa standard for various industries issued by the International Electrotechnical Commission — based on origins, faults can be divided into 3 categories: Random Fault, Systematic Fault, and Common Cause.

Random Fault, as its name suggests, is completely random in terms of what part fails and when it fails. For example, component consumption or aging; even if the same batch of components is produced at the same time, due to different usage or wear conditions, the time of fault occurrence will be different and unpredictable. Sometimes, Random Fault could be caused by human error or negligence, which is also unpredictable.

Systematic Fault, commonly known as ‘bug’, is a problem with the design itself. The failure caused by such type of fault can be reproduced as many times as possible, as long as the same conditions are repeated.

Common Cause refers to the cause of multiple components failing at the same time. For example, environmental factors like high temperature or high radiation.