Keeping the World Flowing
15
4.3.1 Flying Redundancy Slave to Master Connection
Primary Master Backup Master
FR
First Master Second Master
Primary
n
64+n
Slave
Backup
Primary
Slave
Backup
Primary
Slave
Backup
Primary
Slave
Backup
SR
n n
m m
Fig. 8: Profibus DP Flying Redundancy Connection
With FR (Flying Redundancy) the aim is to protect against
a failure of the Profibus Interface. The data highway is
considered to be more reliable than the connection interface.
There is a single data highway and both the Profibus card
inputs are connected to it. The card must be set to FR mode
and it then adopts a fixed offset of 64 between the set
address (used for primary communication) and the backup
communication address.
When the card is powered ‘on’, Channel 1 will be the Primary
channel. If the card does not enter Configuration Mode
within 1 second (because there is no Master present) then
Channel 2 will take over as Primary. Once again, if there is
no communication within 2 seconds, then it will revert to
Channel 1 and now it will wait 4 seconds before Channel 2
assumes Primary status. The switch over time will increase
by a factor of 2 each time until it reaches its maximum of 32
seconds. It will continue to switch channels using a 32 second
switch over time until one channel receives PLC messages.
In the event of a failure of the Primary channel, the Backup
automatically changes to use the Primary address. Hence for
all control purposes the Master only uses the Primary address.
The Backup address can be used for exchanging data but
any commands to move the actuator directed to the backup
address will be ignored. If a configuration message is sent
to the Backup address that is different to the one sent to
the Primary address it will be accepted, but not actioned.
The data exchanged between the Master and the Primary
includes information on the status of the device and hence
the availability of a Backup should the Primary fail.
•
Single Data Highway, two communication ports
•
Channel 1 is Primary on power up
•
Default method is SR mode; to achieve FR parameter
15 must be altered
•
Fixed offset of 64 between Primary and Backup addresses
•
Backup automatically adopts Primary address if
Primary fails
•
V0 cyclic Commands to Backup ignored
•
Reports the status of Primary and Backup to the Master
•
Configuration and Parameterisation changes only over the
Primary address
Single and Dual Data Highway Configurations
A4 US
US
A4
US
A4
A4 US
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