Mode of operation
Siemens PLT130
.
1994
2/4
Redundant operation mode, transmission rel iability,synchronization
Redundant operation mode
TheCS 275 bus system can be redundantin orderto increase
the availability.The interface modulesfor 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 permiss ible between bus A and the re-
dundant bus B.
Thebus system is started up onbus A. Besides this,no prefer-
ence is given to either bus. The bus system carriesout a cyclic
test to see whether a changeover cr iterion is satisfied. An auto-
matic changeover is carried out if this is the case.
Changeover criteria
An image of the local bus is generated t hrough each bus line
approx. every 750 ms. If the image of the passive bus con-
tains moreentries than that of the active bus,the system
switches to the passiv e bus.
If the images on the two bus lines are the same, but the mas-
ter detects a transfer reques t on the passive bus, a change-
over also takes place to the pas sive bus. A slave sends t rans-
fer requests on the passive bus if transfers are no longer
possible for it on the activ e bus.
If the current master fail s because of a fault, the slave wi th the
smallest participant address assumes the mast er function on
the previously passive bus (if one exists) .
The bus changeover is signalled to all bus participants.
Transmissionreliability
In addition to data security of the transmission m ethod, the fol-
lowingmeasures ensure high transmissionreliability in the
physical transmiss ion path:
Noiseimmunity to IEC 255-4
Triple screened cable, redundant
Coarse overvoltage protection in t he building entry (option)
Fine overvoltage protection in t he connector board AF (option)
Deflection of noise using brai ded screens and metal front
plugs
Passive line without ampli fier
Non--reactiveinduct ive coupling
Appropriate signal coding on the remote bus ( bipolar current
signals)
Automatic signal equalizati on independent of location
Balanced (to earth) transm ission
High signal voltages
Electrical isolation of par ticipants on remote bus
Distributed transfer cont rol.
Time synchronization
The real-time clocks of the par ticular TELEPERM M subsystems
are synchronized by signals from an OS operation and monitor -
ingsystem. This can be synchronized by a radio clock ( DCF 77
radio transmitter) or a standard clock.
Thesubscribers on the CS 275bus system must be synchro-
nized with high accuracy. Because of it, t he transit time of the
synchronization message is cor rected within the milliseconds
range by the internal buffers of the local bus interf ace modules
of theautomation systems and programmablecontrollers or by
bus couplers.
Time rece ive
memory
Intermediatetime
counter't(ms)
Transmission
buffer
Dateand time
transmission
program
Remotebus 1
Remotebus 2
Fig.2/3 Time generation, time synchronization
Created with "Chameleon CMYK PDF Creator" for Wolfgang Strozyk at Siemens AG
This catalog is out of date, see note on page 2