wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

33-8 Industrial Communication Systems
Master
(a)
Master
(b)
FIGURE 33.7
The behavior of (a) bus systems and (b) ring systems in the event of a cable break.
a division into different segments. Repeaters, which are placed at specific points, can then perform
diagnostic functions. However, a repeater cannot monitor the entire system; it can only cover a defined
number of devices per segment. Furthermore, the use of repeaters incurs additional costs and increased
configuration effort.
In the INTERBUS system, the user is supported by the physical separation of the system into different
bus segments. As described for the line interrupt, the devices are activated by the master in turn and the
ring is closed prior to the short circuit, which means that subsystems can be started up again. The error
location can be reported in clear text at the bus master.
In summary, the INTERBUS diagnostic features are essentially based on the physical segmentation
of the network into numerous point-to-point connections. This feature makes INTERBUS particularly
suitable for use with fiber optics, which are used increasingly for data transmission in applications with
large drives, welding robots, etc. In linear systems, the use of fiber optics—as in bus segmentation—
requires expensive repeaters, which simulate a ring structure.
33.4 Performance Evaluation
This section considers the performance of INTERBUS with respect to the relevant parameters, such as
the number of I/O nodes and the amount of cyclic I/O data.
The following equation applies to the INTERBUS layer 2 cycle time T IB :
T = 13⋅ ( 6 + n) × T + T
IB Bit SW
where
n is the total length of the SR [bytes]
T Bit the time needed for transmitting a bit
T SW the software runtime of the master
© 2011 by Taylor and Francis Group, LLC