User's Manual

Mode of operation
Siemens PLT 130
.
1994
2/4
Redundant operation mode, transmission reliability, synchronization
Redundant operation mode
The CS 275 bus system can be redundant in order to increase
the availability. The interface modules for the local bus are al-
ready designed for a redundant local bus line. A bus converter
UI and a connector board AF are required for connection of a
redundant remote bus per remote bus cable. Different remote
bus cable lengths are permissible between bus A and the re-
dundant bus B.
The bus system is star ted up on bus A. Besides this, no prefer -
ence is given to either bus. The bus system carries out a cyclic
test to see whether a changeover criterion is satisfied. An auto-
matic changeover is carried out if this is the case.
Changeover
criteria
An image of the local bus is generated through each bus line
approx. every 750 ms. If the image of the passive bus con-
tains more entries than that of the active bus, the system
switches to the passive bus.
If the images on the two bus lines are the same, but the mas-
ter detects a transfer request on the passive bus, a change-
over also takes place to the passive bus. A slave sends trans-
fer requests on the passive bus if transfers are no longer
possible for it on the active bus.
If the current master fails because of a fault, the slave with the
smallest participant address assumes the master function on
the previously passive bus (if one exists).
The bus changeover is signalled to all bus participants.
Transmission reliability
In addition to data security of the transmission method, the fol-
lowing measures ensure high transmission reliability in the
physical transmission path:
Noise immunity to IEC 255-4
Triple screened cable, redundant
Coarse overvoltage protection in the building entry (option)
Fine overvoltage protection in the connector board AF (option)
Deflection of noise using braided screens and metal front
plugs
Passive line without amplifier
Non--reactive inductive coupling
Appropriate signal coding on the remote bus (bipolar current
signals)
Automatic signal equalization independent of location
Balanced (to earth) transmission
High signal voltages
Electrical isolation of participants on remote bus
Distributed transfer control.
Time synchronization
The real-time clocks of the particular TELEPERM M subsystems
are synchronized by signals from an OS operation and monitor-
ing system. This can be synchronized by a radio clock (DCF 77
radio transmitter) or a standard clock.
The subscribers on the CS 275 bus system must be synchro-
nized with high accuracy . Because of it, the transit time of the
synchronization message is corrected within the milliseconds
range by the internal buffers of the local bus interface modules
of the automation systems and programmable controllers or by
bus couplers.
Time receive
memory
Intermediate time
counter ' t(ms)
Transmission
buffer
Date and time
transmiss ion
program
Remote bus 1
Remote bus 2
Fig. 2/3 Time generation, time synchronization
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This catalog is out of date, see note on page 2