Profinet Spoken on the Plant Floor

July 21, 2008
Siemens Workshop Participants Configure for Ethernet Communications

Configuration was the name of the game at “Ethernet on the Plant Floor,” one of the pre-event technical hands-on workshops at the 2008 Siemens Automation Summit. Siemens’ Stefan Sattler, Profinet marketing manager, and Tim Hurtt, automation applications engineer, walked participants through a detailed configuration of demonstration equipment using STEP 7, along with a PN OPC server and Simatic WinCC flexible HMI software.

“Ethernet is just the wire,” explained Sattler. “Profinet is the protocol. Profinet is an open solution. If you want to exchange data fast, you need a fast protocol. Profinet gives complete control of the manufacturing processes.”

“At the administrative level, they want maximum visibility so they can see the data. But below the administrative level, we have things we need to accomplish.”
Because of increased demand for information and reporting, network developers arrive at unique challenges, said Sattler. “At the administrative level, they want maximum visibility of the other areas, so they can see the data, and it can be forwarded,” he said. “But below the administrative area, we have things we need to accomplish. This creates challenges for things like simplified network design, implementation and expansions, optimized network performance, plant-wide engineering and production flexibility, data security and the large data volume in the office world vs. reliability and availability in the plant.”

Profinet gives complete control of manufacturing processes, explained Sattler, with the capability to implement distributed I/O, peer-to-peer communication between control platforms, data acquisition, machine safety and motion control; and it gives the ability to incorporate infrastructure and network management and data security.

Participants in the workshop worked in pairs and used demonstration equipment comprising two units. The first unit included a power supply, PLC, switch, I/O module, security and a conveyor. The second unit contained similar components, swapping out the security module for a gateway.

Under Hurtt’s guidance, participants configured the hardware in the STEP 7 environment using the Simatic manager. “You have engineering tradeoffs in any PLC,” said Hurtt. The more I/O you add, the slower the data. But it takes an awful lot of hardware to choke an Ethernet network. When you look at I/O processing and the amount of time to process your program logic, you have a finite amount of time. It’s still going to be deterministic, but you’re just taking away from the processing time slice.”

Profinet helps with diagnostics, too. “You can have the ports monitor specific connections and report errors,” said Hurtt. “You can insert a switch into a processor so the processor can monitor the I/O. In Profinet you have these update times. If you don’t get an update in a certain amount of time, the I/O is going to generate diagnostics. There are a lot of mechanisms in play to make sure your I/O is updated. And in STEP 7 architecture, any time you have a fault, you can make adjustments. Any module that fails in the field can be replaced.”

Profinet diagnostics can predict, detect, locate and resolve failures, added Sattler.

The workshop also addressed the need for peer-to-peer communications using Profinet. “Hardwired is fine, as long as you don’t have too many solutions,” explained Sattler. “Profinet CBA is addressing this challenge.” Profinet CBA, the fieldbus protocol for platform-independent data exchange, should allow a user to use anyone’s tool and pull anyone’s PCD files, added Hurtt.

“A machine needs to exchange data with other machines,” explained Sattler. “Profinet eliminates communication programming and debugging, and it reduces time and cost in engineering and commissioning.”

In a typical situation, said Sattler, you have a number of steps including program communication, definition of the data to be exchanged, adapting the code in the controller and implementing diagnostics. “In a big installation with multiple complications, this can be time-consuming,” he said. “Profinet allows you to configure instead of program and debug. It simplifies the interoperability between multiple vendors.”