Redundancy Functions With Addfem - Siemens Add 7 AddFEM Manual

Mode of Operation
3.3

Redundancy Functions with AddFEM

Increasing the Availability through Redundancies
Redundancy in this context means the implementation of a "1–out–of–2" structure.
The availability is increased by the parallel use of two identical components. If a
component fails due to a fault, the second component takes over the function bum-
plessly. Extensive redundancy mechanisms and self–diagnostic functions which
are integrated in the AddFEM ensure automatic error recognition and changeover
without any manual interventions being required.
Master/Reserve
The terms "Master" and "Reserve" are used in order to identify the two AddFEMs
in the following sections. The reserve operates simultaneously with the master and
not only in case of errors. The process outputs of the reserve are, however, pas-
sive, meaning that no signals are output.
Features of Redundant AddFEMs
When an AddFEM fails the system changes over automatically to the redundant
unit ("1–out–of–2" structure). Smooth taking over of the master state by coupling
via the optical–fiber cable redundancy interface.
The changeover in the master state initiated by the AddFEM after error recogni-
tion, meaning the switching–off of the outputs of the previous master and swit-
ching–on of the outputs of the previous reserve is carried out quasi smoothly.
(for tolerance–specific changeover gap refer to "Technical Data" Section 4.1)
Optical–fiber Cable Coupling
Between redundant AddFEMs there is a serial bi–directional "redundancy" commu-
nication by means of optical–fiber cable through which the error status, redun-
dancy status and update data are exchanged.
Master/Reserve Specification
In case of error equilibrium of the redundant AddFEMs specification is carried out
by the AP. This soft specification is also used for the cyclic M/R changeover (every
24 hours).
Forced Reserve Specification
In case of a missing or faulty optical–fiber cable redundancy coupling the master/
reserve assignment is carried out by the AP.
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C79000–G8076–C900–03