In SIL certification, we know that failure rate is a very important data. Once we obtain the product failure rate, we can determine whether the product meets the requirements of the corresponding SIL level, whether modifications need to be made, and what the direction of modification is. Therefore, in the Chinese SIL certification standard GB/T 20438.4-2017, we can know the two methods for determining failure rate.

The first method can be called theoretical calculation. We can use a failure analysis tool like FMEDA to obtain the total failure rate of the entire product based on the inherent failure rate of each component. In this process, we rely more on mathematical tools and the application of functional safety principles to obtain mathematical and theoretical data.

Another method we can refer to as empirical analysis, which is based on statistical principles. Its specific method is to collect the number of failure events that occur throughout the product's service life cycle, and determine the frequency of a failure event. When we collect a sufficiently large sample, statistical principles tell us that the frequency of this failure event will approach a fixed value, This fixed value is the inherent failure rate of this product.

Through the analysis of these two methods, we can clearly understand that when a new product is launched, we often use the first method for SIL certification, while for a traditional product, using the second method for SIL certification is more accurate.