Not All PROFIBUS Devices are the Same

Example 1

While troubleshooting a PROFIBUS network last week, I learned that Emerson’s Delta V PROFIBUS controllers are a bit different from what I expected.

The number of devices this controller DeltaV™ S-series PROFIBUS DP Interface Card supports is 64 vs. the 128 that are available. There are likely many networks that have fewer than 64 devices. This could be a cost-effective option. The baud rate is also limited to 1.5MB, which again is sufficient for most networks.

Upon connecting PROFITRACE I did notice that the voltage coming from the controller was low. The design engineer understanding this put a repeater in the same cabinet so that this would not create any network performance issues. The design engineer created the network to be as robust as possible as this was for critical infrastructure – a water treatment plant. I suspect that the limitation of the 64 devices and baud might also be a hardware limitation due to the low voltage reading.

Example 2

Last month I was on site for a PROFIBUS troubleshooting call. They were utilizing Siemens repeaters (6ES792-0AA02-0XA0). After hooking up Profitrace all the signals and voltages looked good at the PLC. Utilizing the DB9 connector on the repeaters the signals again all looked good. Later I learned that the segment that you end up looking at on the Siemens repeaters is not from the repeater to the end of the segment, but from the repeater to the PLC. The likelihood of having issues in that direction is a tiny fraction of the issues caused by slave devices.

The Siemens repeaters are also well known for being hard to wire and easy to miss-wire. The terminals are deep inside which means that most Electricians will bend the wire tight to get it in which can damage the wire. The markings are not clear which is in and out. Segment one comes in on the top left and out on the top right. Segment two comes in on the bottom left and out on the bottom right. Any variation on can mean you either are not repeating or you are missing termination.

Recommendation

This is the reason I like the PROCENTEC B5+R series hubs.

• Galvanically isolated channels – isolating noise on the network.
• Does not require PROFIBUS connectors – saving money.
• The DB9 connector allows you too look down every segment with a PROFITRACE where you will have issues.
• Wiring is clearly marked.
• LED help you troubleshoot.
• Communication redundancy availability.
• Ability to create different network topologies.
• Error messages can be integrated into COMBRICKS.
• Cost effective!

Find out about the risk of using uncertified PROFIBUS devices and the process for certification at a free Procentec webinar on May 25th 8am MD // 10am ET. Register to attend, or to receive a replay link.