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from the department...
Difference between PROFIBUS and Industrial Ethernet
Communications systems and equipment. topic
Posted by Jose Sousa on 22 February, 2002 - 11:54 am
I will take a decision to choose a method of communication between S7-300 PLCs. I do not if i use PROFIBUS or Industrial Ethernet. Can anyone give some help.

Best Regards

Josť Sousa


Posted by CJ on 23 February, 2002 - 11:03 am
PROFIBUS is A Token Network base on RS485,and for that is more safe. Industrial Ethernet is, as the name tell, Ethernet,faster but less safe.

Best Regards
CJ
for more information go to "http://www4.ad.siemens.de/":http://www4.ad.siemens.de/


Posted by David Lawton on 24 February, 2002 - 12:43 pm
If your network will purely be Siemens kit I'd stick with Profibus. If you have other manufacturers kit involved I'd be tempted to go
ethernet. The other thing to consider is the comms speed vs. how robust it needs to be, as mentioned already


Posted by R.A. Hulsebos on 24 February, 2002 - 12:52 pm
Can you explain why the presence of a token
makes a network more <quote>safe<unquote> ?

Ethernet isnt always faster than Profibus
either, because it has a much larger overhead,
and the 10 Mbit/s is just used to compensate
that. Do some calculations before you make
a decision!

Rob Hulsebos
rahulsebos@cs.com


Posted by david mertens on 25 February, 2002 - 10:44 am
Both networks can be used for this type of communication with the same reliability (When S7 connections are used in both cases) and the same
programming effort. The costs will also be similar (CP341-1 versus CP341-5), both systems offer the possibility to construct redundant
rings, etc... However, the future trend is more towards ethernet. One advantage of industrial ethernet is speed, up to 100Mbit/s versus
12Mbit/s for profibus. Future releases of siemens CPU's will have on-board ethernet connections, making this the default standard for
communication.


Posted by Gabriele Corrieri on 26 February, 2002 - 3:49 pm
I not agree these opinions ... I'd remember that only ProfiBus (and all of
other fieldbus, but not Ethernet) is deterministic ... the cyclic query on
slaves on ProfiBus is time-determinated by token-passing, on Ethernet there
is a CSMA/CD, otherwise called "casual access to bus" (is not the
explanation of CSMA/CD but is very near to the reality), every
bus-partecipant access to bus only when it had to exchange datas, and for
example can access to bus for more times consecutives, or on the contrary
not access for more times, then there isn't a unit-fault-check on bus, and
the datas could arrive after *a not determinated* time before are avaiable
on slave.
Ethernet, vice versa is more fast than ProfiBus or other FieldBus (I'm not sure that is more fast that LINK2 of Eurotherm Drives), and is more simple to admin than Profibus and is designed specially for high levels of ISO/OSI
"tower": is design to communicate from PLC to SCADAs, to office, administration, delivering ... (don't lost that first release of Profibus
was called FMS FieldBus Message Specification, and now we talk on release called DP (decentralized periphery) made for low-level osi tower.)


I'd excuse for my very complicate explanation, and errors that I wrote ... but I invite everyone that is interested to write me directly.

Gabriele Corrieri

gabriele.corrieri@tin.it


Posted by Friedrich Brabandt on 25 February, 2002 - 2:32 pm
For communication between Modicon and Siemens S7-300, i have used the Siemens Communcation-Module CP341 with loadable Modbus-Master Driver.
Siemens is Master, Modicon is Slave. I used this type of communication several times with Siemens S5, S7-300, S7-400.

kind regards

Friedrich Brabandt

Germany


Posted by Roland Clayton on 25 February, 2002 - 3:21 pm
Big difference may be that Ethernet can run 4-500M at 10Mb where as Profibus DP runs 100m at 12Mb before using some form of a repeater.
Some customers require the I/O to react/inform of a problem rather than wait for the token and favour Ethernet and could can run at 100Mb.

Regards
Roland Clayton
Certified Profibus DP Engineer
Schneider Electric UK


Posted by Rick Hudson on 25 February, 2002 - 3:41 pm
The speed issues look good (100 Mb vs 12 Mb) but what about the effect of Ethernet's overhead message requirements?

Rick Hudson


Posted by Tim Linnell on 26 February, 2002 - 2:37 pm
I missed the original post, but assuming it related to machine building (remote I/O and devices) as opposed to higher level PLC to PLC comms, it's unlikely the notional speed benefits of Ethernet will provide any tangible throughput increases, as the latency of the slaves will be the dominant factor, with the ability of the master to process the data also limiting proceedings.

The glib answer to the question in the header is that the difference between Profibus and Industrial Ethernet is that Profibus exists! It is widely supported by multiple vendors in a standardised format. Industrial Ethernet really has no multi-vendor standard apart from Modbus TCP, which means returning in effect to a suck it and see approach to any form of interoperability at a device level (Profibus on Ethernet and ControlNet on Ethernet are currently way beyond implementable on smaller slave devices, and apparently aimed more at higher level boxes). Great if you are a large vendor who can guarantee interconnect, very bad for multi-vendor mix and match systems.

If it were my plant, I would use Profibus to construct machines without hesitation - it just works better than anything else in this context. I might consider Ethernet at the next level up, into production planning, summary SCADA and ERP.

Will Ethernet be the default standard for industrial comms? Had you asked me that 18 months ago I would have been very confident that this would happen. I'm less so now having looked closely at the question. It adds cost and complication with no clear benefits, and as I've said in other contexts on this group, I think the adoption of Modbus TCP on Ethernet will actually
tend to promote use of RS485 Modbus subnets gated into an Ethernet uplink device, and thereby limit the downwards reach of Ethernet.


All views personal, of course.


Tim Linnell (Eurotherm Controls)

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