Siemens Add 7 AddFEM Manual page 45

Mode of Operation
Master–Reserve Logic
Transfer of the master state is always carried out via the error weight. A numerical
comparison of the error weighting is carried out to this purpose:
IF OWN_ERROR_STATUS < PARTNER_ERROR_STATUS
If redundancy communication via the optical–fiber cable interface fails, the higher–
level system decides on the master state.
Master–Reserve Assignment
The master–reserve assignment is changed by:
S Specification (MRV) of a desired master by the AP if the error weighting of the
redundant AddFEMs is the same
S Specification of a forced reserve (ZRV) by the AP if the redundancy communi-
cation fails
S Failure or STOP of the master AddFEM
S A greater error weighting at the master than at the reserve
Error Weighting
The own error status is sent back to the AP with the channel error weighting as the
"error weighting". The error weighting is defined as follows:
Channel Error Weighting
The lower–level channel error weighting is formed by the sum of the individual
channel errors. All the channel errors (analog input, analog output and digital out-
put) are weighted equally. The weighting of a channel error is 1. If an external
power supply for the binary outputs fails, the weighting is 8 (since eight binary out-
puts are affected by a failure).
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THEN MASTER
ELSE RESERVE
Error weighting = Error status + Channel error weighting
AddFEM
AddFEM
C79000–G8076–C900–03