OK to use DP for HMI and datalogging services.

Calling all Profibus experts.

I am considering to use the S7 CPU 315-2 as a standard device for our various control tasks/machines.

In that context, I would use the built-in DP port to connect all the CPUs in a network with common HMI and datalogging services.
The built-in MPI port would be used for a small local HMI at each CPU.
I have no need to use DP for i/o expansion.
I will use Siemens Protool Pro for the common HMI and Siemens OPC for the datalogging.

Coming to the point:
Siemens states that DP should primarily be used for i/o expansion.
Are there any problems or penalties in my proposed layout, as it seems to use DP for other tasks than the intended ?

I would like to avoid having to invest in CP modules or in repeaters for the MPI network.

I can't remember if the 315-2DP will do it, but I use FMS with a S7-414 instead of DP for data transfers. DP is designed for time critical apps while FMS was designed for massive data transfers.

BTW, which HMI have you decided on?

hello;
There are possible problems only if you try to use DP for HMI connections ans I/O expansions at the same time, because the timing requriements for I/Os could be disrupted by the HMI master class 2 (especially if there is more than one).
In your case, and as I presume the HMI will be Siemns TPs (Protool only programs these), then DP is an excellent choice, fast, reliable ans easy to configure. The only thing you have to check out is the bus length, as the bus speed decreases with distance (100m allows 12 MB, 500 m 1,5 MB, 1000 m only 9600 bauds (without repeaters)).
Hope this helps,
Daniel Chartier

Dark Knight,

I am going to use either Siemens OP270 (for each PLC) or Protool Pro RT (common HMI).
My grand idea is to standardise all code and HMI to such a degree, that I can tailormake each aplication, and still have reusable code.
In that way, I can standardise on diagrams, PLC code, HMI code and user manuals.

But I now see one little snag that could bring the whole thing down:
The alarm and message system in Protool is based on some "area pointers". And these seems to be definable for only one connection (PLC) at a time. I cannot have the critically important alarm system work with multiple connections.
I have to investigate this a bit more.
It is a pity if it doesnt work, as I would like to be able to share HMI code between OP270 and Protool RT.

Thank goodness, Protool CAN split the alarm message area between several PLC's .
I found out by experimenting. Protool online help does not provide a lot of info about connecting to several PLC's at the same time.

Daniel,
I will probably run DP at 1.5 Mbaud. Remembering how I have run AB RIO networks at 57 kbaud, I cannot help thinking that there should be enough bandwith to run several masters on the bus and still be able to have some i/o. It is not my plan though, to have i/o on the DP network. But who knows what the future brings ?