All items on Profibus

Gents, we are looking at a very large new installation. The philosophy is that we get "everything" onto profibus DP. All VSD's, some motor controllers, all analog (and some digital) instruments, remote IO bases, every thing that can be profi dp, will be profi dp. What issues should we expect (besides limit to numbers on drops)?. Is this a good idea? Will the system be stable and reliable? PLC will be Quantum or Seimens S7. Your thoughts please.
Regards
Steve D

Hello Steve;

In the past few years, we have been setting up District Cooling plants on the same philosophy as you are thinking of.
All MCCs and VFDs on one DP network; all DP instrumentation (flowmeters) and Profibus-PA instrumentation (temeprature, pressure and level transmitters) on another network along with the valves (ON-Off and modulating); another network for power monitoring (protection relays, thermal relays, softstarters for the chillers...). We also have Modbus networks to connect to vendor's equipment that cannot be setup on Profibus.

We could have done the same with DeviceNet/Controlet, or maybe Ethernet I/O (protocols like Ethernet I/P or Modbus/TCP), but it was easier to find vendors in our equipment lines that would connect to Profibus.

On the plus side: simplicity in the wiring design and setup; increased diagnostics tools embedded in the DP-Masters.
On the minus side: learning curve for programmers(you must allow for development time on your first projects), operators (diagnostics, maintenance and servicing are different) and installers (minimal); increased cost per node (offset by lower installation and commissioning costs); more attention to be given at design time to topology (length of segments, number of nodes per segment, use of repeaters, bus speeds, multimaster operations...).
We use Controllogix platforms with Prosoft MVI Profibus masters, or GE Fanuc RX3i with their own master modules, depending on the client requirements. We are starting our 5th plant on this design, and find that for instrumentation we have reduced wiring and commissioning costs/time by almost half compared to our traditional digital/analog I/O schemes. The extra node cost is offset by the lower number of I/O cards and PLC panels required, wiring is simpler and more efficient, diagnostics are more efficient. Most commissioning problems we have had to face were linked to faulty installation of connectors, or repeaters.

Be prepared to spend some time on the line with vendors, especially to get the correct GSD files for their products, and expect them to help you out with comm problems on their equipment. They should feel comfortable enough with Profibus to be able to help you out efficiently.

Hope this helps,
Daniel Chartier

Hi Steve.

Your suggestion to a new system philosophy is the same that we pursue.
It has been a great success so far. We try to put the Profibus i/o as close as possible to the proces.
The only thing that we have not yet put on Profibus is the safety system, but it is the next step that we will take.

One suggestion for you is to include a Profibus repeater with diagnostics capability in each line.
Particularly if keeping downtime to a minimum is a high priority for you. It kan help locate problems that are not related to programming or configuration errors, such as cable and connectors.

One other item is the "ownership" of the network. When you get many different manufacturers' products all connected together, who is responsible when it doesn't all quite work as expected? Clearly your are the final owner of the specific installation and will have to accept the responsibility for it functioning as you want. But I would try to get some indication from the supplier of the master that they acknowledge control and diagnosis of the network is down to their device alone. Provided you've installed and configured the slaves correctly there's not a lot a slave supplier can do for you. His devices just wait to be spoken to. Get the master supplier on your side right at the outset - his device controls everything.

Regards

Ken