Control Via Multiple Masters on Profibus DP

MorphuisOGrady

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Could anyone from a Siemens background offer me some advice here.

I have a spec here which is requesting a system where until normal control a DCS system will control Simocode Pro V slaves on Profibus DP. However sometimes it will be desirable to have another PLC controlling the Simocodes.

Is it possible to have 2 DP masters controlling slaves?

I suppose the real question is...Can I control Simocode Pro V slaves from 2 Masters on same DP network?
 
Last edited:
Hi there,

I am by no means a Profibus expert, but I do know that a Profibus slave cannot be shared by two masters.

//Patrick L
 
Not an expert in Profibus myself.So is there anyway to control the slave from second master via some other form of data exchange? Messaging etc?
 
The only way, as I see it would be if the two PLC´s could communicate and I think the Siemens PLC´s can communicate. One PLC communicates with the slave and the second PLC communicates with the first PLC, which forwards data to/from the slave.
How this would be done configurationwise, I have no Idea, but I am sure that Siemens support should be able to answer.
 
Can I control Simocode Pro V slaves from 2 Masters on same DP network?
Click to expand...
No, at least not at the same time. You can configure the slave on both masters, but the one that gets connected first is the "real" master. The second master will give a buss failure until the slave is available again (when the first master goes offline). I've never seen this setup before but it can be done if that is what you want.
You could use a DP-DP coupler to communicate between the two masters and configure the Simocode in the DCS. In the DCS program you can write some code to use the control bits from the PLC if this is requesting the control. This does require the DCS to be operational when you want to control the Simocode through the PLC.
 
Thats what we have done in the past using inter PLC comms to control the Slaves with one PLC being the Master.

The client has requested that both their PLC/DCS and our PLC have control over the slave.

What I need is some way that I can switch control from 1 Master to the other. What if bot Masters where S7 PLCs. Could this be done via code?

Thanks
 
There is a SFC12 to activate and deactivate slaves. Maybe this could be used for this purpose but I would have to test this myself on a test rack.
 
Why does the client want such a haywire solution? Does the DCS die often? Or are the Simocodes running very important functions that are not allowed to stop? Be aware that the simocodes can be set up to keep the running state if the master fails. There are also possibilities to run a simocode from its inputs (OR or AND -function with the bus commands).
K
 
KalleOlsen said:
Why does the client want such a haywire solution? Does the DCS die often? Or are the Simocodes running very important functions that are not allowed to stop? Be aware that the simocodes can be set up to keep the running state if the master fails. There are also possibilities to run a simocode from its inputs (OR or AND -function with the bus commands).
K
Click to expand...

No idea why the client has requested this but thats what they want.

I'm hoping there might be some way to release slaves from one Master to allow the other to take control? Of course not being an expert this could be pure nonsense!
 
Hello MorphuisOGrady,

You can have multiple masters on the same Profibus network. Use Profibus FMS as allows Token Ring communication which alternates between masters in a configurable time period. Siemens has those FMS communication modules.

Note: The FMS network has to be separated from the DP network though.

Cheers,
Wassim Daoud
Global Solutions Architect
www.MatrikonOPC.com
 
As far as I know, the Simocode does not support FMS (any more).
What about adding one more PLC that only controls the Simocode bus, and let it act as a gateway that select the control master between the DCS and your PLC?
 

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