Many techniques are useful in evaluating the expected reliability of a system, but the Reliability Block Diagram technique (RBD) is one of the most useful. An RBD is drawn using simple blocks to model the elements of the system that can have an impact on reliability. Static components that have little or no effect on reliability are frequently ignored. There are two forms of RBD analysis. One uses simple mathematical expressions to calculate the anticipated system reliability. The other uses a number of life-cycle simulations to determine the expected reliability performance based on statistics.

Let's discuss the approach using simple mathematics. (A number of commercially available simulation models can be found on the internet and that resource is left to the reader to explore.)

The first step is to understand the most basic element., of the Reliability Block Diagram.Depending on the level of your analysis, an individual box can represent a small part, or a complete operating unit or plant. In either instance, the number in the block represents the expected reliability of the element that the box represents. The reliability of that element is calculated as follows:

Where,

R(t) is the reliability or likelihood of operating for the period of time t without a failure.

** represents "to the power of" the following exponent.

mtbf is the mean time between failure for the element represented by the box.

For instance if the mean time between failure is one year and the time interval of...