## What is reliability importance and how is it used in BlockSim?

Reliability importance is a measure of how much impact each component has on the overall reliability of the system. This can be useful information for improving the system reliability, because you will want to concentrate your efforts first on improving the reliability of the components that have the greatest effect on the system reliability.

One simple way to demonstrate reliability importance is to look at a series system. In general, the least reliable component in a series system has the greatest effect on the reliability.

Consider three components arranged reliability-wise in series, where R1 = 70%, R2 = 80% and R3 = 85% (for a given time). In the table shown next, we can examine the effect of each component's reliability on the overall system reliability.

The first row in the table shows the given reliabilities for each component and the corresponding system reliability. In each of the subsequent rows, the reliability of one component has been increased by 10% while keeping the reliabilities of the other components at the given values. This allows us to observe the effect of each component's reliability on the overall system reliability. It is clear that the highest system reliability occurred when the reliability of the least reliable component (Component 1) was increased by a value of 10%. In other words, Component 1 has a higher reliability importance.

 Component 1 Component 2 Component 3 System 0.7 0.8 0.85 0.476 0.8 0.8 0.85 0.544 0.7 0.9 0.85 0.536 0.7 0.8 0.95 0.532

In simple systems such as this series system configuration, it is easy to identify the weak components. However, this becomes quite a difficult task in more complex systems. The value of the reliability importance depends both on the component's reliability and its position in the system. Click here for more information about how reliability importance is calculated in BlockSim.

In BlockSim 8, this value is used in several places.

• You can view the reliability importance of the blocks in an analytical diagram in three plots:
• RI vs. Time shows the reliability importance of the components over time.
• Static RI shows the reliability importance of a specified number of components at a specific time.
• Static RI Tableau shows the static reliability importance in tableau format, where each component is represented as taking up a certain percentage of the overall plot area, thereby giving another visual representation of how the reliability importance values compare.
• Reliability importance is one of the factors taken into consideration by BlockSim's Allocation Analysis tool, which helps you to determine the best way to achieve your system reliability goal by improving the reliability of individual components.
• Analytical FRED Reports illustrate the reliability and reliability importance of a system’s components in a flexible, color-coded format. These reports can be used to easily identify the components most in need of improvement in order to achieve the desired system reliability.