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S5-115F Manual
9
Reliability, Availability and Safety of Electronic
Control Systems
The terms reliability, availability and safety of electronic control systems are not always clear and
sometimes even misinterpreted. This can be explained on the one hand by the different failure
characteristics of electronic control systems compared with conventional systems. On the other
hand, some of the safety regulations have been made considerably more stringent in a number of
application areas in the course of the last few years.
The following chapter is intended to familiarize you with the basics of this problem complex and
to show how optimal reliability is achieved in the S5-115F.
9.1
Reliability of Electronic Control Systems
Reliability is the capability of an electronic control system to satisfy, over a specified period and
within the specified limits, the requirements placed upon it by its application.
Despite all the measures taken to prevent failures, there is no such thing as 100 % reliability.
The failure rate
is a measure of the reliability.
n
=
N
x t
o
EWA 4NEB 811 6148-02
Reliability, Availability and Safety of Electronic Control Systems
n = Number of failures during time t
and
N
= Remaining components
o
9-1
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