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Old July 8th, 2010, 11:20 AM   #1
Jeff23spl
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PRofibus network with more than 1 Master

Hello Guys

i may ask directly Jesper but maybe someone else can give an interresting answer

I have a project with a PN/DP plc and the customer would like to use my profibus network to connect instead of the Ethernet availaible

The 315pn/DP is configured as a DP master and control 8x S7-200 slave. Can it be possible to include a Scada system as a MAster also on this network....

I not sure but i think as long as it is a Scada/HMI it may work but if 2 PLC are Master on the same network it won't work ? i'm i right ? I believe that because i used an S7-317 2DP to get 2 separate DP network the last time i did that and it worked fine with the 317 being master on 1 and slave on the other....
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Old July 8th, 2010, 02:07 PM   #2
tim2
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Basically, I think you're right.

Typically an HMI On the network is not considered the same type of master as the 315. I think the HMI is considered a Master Class 2 and the CPU a master class 1. They can co-exist fine.

Two CPUs as master's don't play together so well.
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Old July 8th, 2010, 03:27 PM   #3
JesperMP
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Yes, several masters can co-exist on the same profibus cable, and each master can have its own slaves, and the masters can send data to each other. Additionally, one or more HMIs which are also masters (but with no slaves attached) can poll data from the PLCs.

There are some gotchas though.

The performance is much decreased with respect to how fast the masters can update the i/o of their slaves. Something like a factor 5-10 slower (!).

The combined multi-master system is much less flexible with respect to how it can be modified on the run, and how nodes can be attached or removed dynamically.

And, one fault can bring the all master systems down.

Because of this, I really recommend to at least put the higher level comms (CPU to CPU, HMIs and SCADAs) on ethernet, and if needed i/o on lower level Profibus (mono-master) or Profinet.
Today, ethernet is the answer. It is also not expensive. Think ahead. Will profibus be as widespread just a few years from now ?
And as your CPU already has a PN port, and your SCADA most certainly has ethernet, why even start to consider to put the SCADA on Profibus ?
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Old July 9th, 2010, 11:21 AM   #4
Jeff23spl
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thanks for ideas

Profinet is a futur option but this project as already been designed, installed and started with S7-200 as profibus slave.
DP module VS ETH module on the 200 have a 3x price difference factor to be considered too...

The other factor is that this project is actually at many hundred miles from my office....
Project sold in 2005 but started only last year....

So i was right to tell the customer to stay away from my Profibus network and try to connect to Ethernet instead...

I will...make new project with 1200 on eth as slave and maybe using profibus port for Scada or also using Eth....i'm looking at that and, to play safe: Waiting for a while to see improvement on the 1200 itself and the software
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Last edited by Jeff23spl; July 9th, 2010 at 11:23 AM.
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