## System Reliability

The discussion in Section 11.7 developed the exponential distribution as most directly applicable to the matter of component and system reliability. In this section, we further elaborate on a few reliability calculations. We define the hazard function for a system or component as h(t) = T—b (11.32)

If the distribution in question is exponential, then h(t) = X exp(- X/) = X (11.33)

which is therefore a constant hazard or failure rate. Under these conditions, the system or component has no ''memory'' and, technically, does not wear out. For most types of purely electronic equipment, this is a good approximation. For mechanical equipment, this is usually a poor model and should not be used. Instead, the Weibull distribution is a better choice.

For the exponential, then, the probability of failure-free operation to time t is

where R(t) is the reliability and X is the constant failure rate, which, in turn, is equal to 1/MTBF.

## Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

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