6
7
Repeaters can also be used to get additional fieldbus lines at a low cost if placed at PLC output.
Each line is independent from the others and therefore a problem on a line does not affect the
others.
BERNARD CONTROLS can supply weatherproof or explosion proof repeaters.
Redundancy
Redundancy of the fieldbus system is to continue to communicate with the actuators even if a line fails.
In order to achieve this function all the communication system is doubled. The PLC uses two output
Profibus ports, the fieldbus line is doubled and the actuator interface board is doubled.
If repeaters are required, the repeaters are doubled.
The redundant INTELLIBUS module is designed according to Profibus Guide Line «Specification Slave
Redundancy» N° 2212, that includes a redundancy communication channel (RedCom) and special
redundancy extensions. One of the slave module acts as primary and the other one as backup.
In fact the Profibus system allows different level of redundancy:
Flying redundancy
is a redundancy of the connection point, the actuator interface is doubled and
also the PLC interface. The line (Profibus cable) is a single line.
The redundant actuator interface INTELLIBUS has 2 channels, each one is connected to the Profibus line.
The address is not the same for each channel. One address is chosen from 1 to 125, the other one
is this a 64.
System redundancy
is the most common system with all communication system doubled as des-
cribed first.
Transmission baud rate
< 93.75 kBit/s
187.5 kBit/s
500 kBit/s
1,5 MBit/s
Maximum line length
1200m
1000m
400m
200m
PLC
Note:The PLC is also at
the end of the line and
needs a termination
To make a detour use
2 cables, up and down.
End of line actuator
Termination is «on»
No ramifications
3.6
EmERgENCy SUPPLy
The actuator is normally supplied by the mains but in case of loss of power supply
an emergency supply could be used to continue to communicate through the fieldbus. This emergency
supply needs 24V DC 4W.
3.7
PROFIBUS DP ARCHITECTURE
Single line
The Profibus cable coming from the PLC is connected to the first actuator then the Profibus cable
links this actuator with the next one and so on. All actuators are connected to the line one after
the other until the last one. No return to the PLC is required.
To avoid reduced performance in transmission don’t add ramifications on the line
Maximum line length is 1200m (3600ft). Maximum number of actuators by line is 31.
Maximum line length is reduced according to the communication speed:
An end of line termination must be connected at each end of line actuator. (see § 3.3)
Repeaters
Adding repeaters modules allows to increase both the number of actuator on the line and total
line length. Each repeater uses one connection point therefore this limits the number of actuators
by segment to 30 units and allows to lengthen the line by 1000m.
According to the type of repeater, it is possible to use until 9 repeaters and to extend the line
as long as 10 km.
Maximum number of actuators depends of PLC capacity, addressing capacity and number of segment
with repeaters. The maximum on one Profibus line is 124.
The important advantage of the repeater compared to other repeater-free technologies is to keep
the communication speed unaffected and therefore to get a very short response time.
Repeater
power
supply
Segment 1000m long
30 actuators
Segment 1200m long
31 actuators
Repeater
PLC
Repeater
Repeater
PLC
Single line
Redundant PLC
Redundant
INTELLIBUS
Redundant
INTELLIBUS
Primary
PLC
Backup
PLC
Redundant PLC
Redundant line
Redundant
INTELLIBUS
Redundant
INTELLIBUS
PLC
Master 1
PLC
Master 2
