Hi,
It is not very clear from BOL where the cable shield should be connected. For now, we have like this:
Left card is H1 with integrated power and the right one is the Profibus (the card is sitting at the middle of the segment with its terminator OFF).
It is clear that in the case of the H1 card, the shield has to be connected at one point, and that point is the ground bar of the 8-wide carrier (this in turn has to be connected to ground).
But for Profibus my research was inconclusive: should it be connected also to the ground bar of the 8-wide carrier or should it be connected to terminal "S" of the Profibus card (as shown on the picture)?
Could someone clarify this?
Thank you,
Istvan
Hi
Sorry, no special experience with Profibus wiring, but, if that can help, remember that cable shield must be connected to (electronic) ground only at ONE side.
If you connect shield by both cable sides, you will create a capacitor !
Choose the side where the ground have the best quality.
In reply to Jack_France:
Check, but I believe I saw 0 Ohms between the S and ground bar, so I'm going to assume it doesn't matter. I understand the confusion, as the BOL picture shows the S terminal isolated.
The Profibus Installation Guide (clips below) does recommend grounding on both ends, but not when connected to IS systems.
In reply to Travis Neale:
The DeltaV Technical Documentation team saw this thread and made some updates to this section of DeltaV Books On-line. I wanted to share this advanced copy with members of this track.
In reply to Jim Cahill:
Thanks Jim. People seem to have strong opinions one way or another.
Profibus recommends grounding shields at both ends.
DeltaV recommends grounding Profibus shields on one end only.
Are they willing to add some basis for their decision to go against Profibus foundation?
I've always heard the German plants had grounding grids that were truly equal-potential, and that's why they could get away with it.
Does it depend on where you are (the quality of your grid? Can it handle a transient between points without harming your thin shield?)
Profibus is a balanced digital signal. Hasn't dual grounding been shown superior for this with it's RF protection taking precedence over any ground loop concerns?
verwertraining.com/.../InstallationGuideV9_2.pdf
www.compliance-club.com/.../020514.htm
www.epanorama.net/.../cable_shielding.html
Sincerely,
Devil's Advocate
Hello guy´s
I´ve been working with Profibus since 1995, and you ALWAYS have to use the end resistor at the end of the line or active end resistors. The shield have to be grounded properly as in the pictures in the earlier messages. I have some times run into factories were you had to ground the profibus wire at several points from the slave to the master. Now when plants are using more and more FVD:s that causes HF disturbant the, importance about grounding just grows. Normally the TE is connected to the PE, so you can´t always count on that beeing without disturbance.
If you are going to use Profibus in a harsh enviroment or the wire is a little bit longer, use optical cable :D
edit: Use the original Profibus connectors in slaves, once we got a batch from some manufacturer where the end resistor connection was broken on the circuit board inside the connector.. it was fun to find why the bus didn´t work :p
Niklas Flykt
Klinkmann Oy
Key Account Manager safety products
nikfly@gmail.com
In reply to Niklas Flykt:
Thanks Neal for the links. The Installation Guide has a very good description of the shield requirements and how to deal with differential voltage between grounds. (section 7.5). I'd heard this before, but they suggest that an Equalizing Cable be installed that will pull both grounds to the same potential, so that current does not flow through the screen. Atlernatively, one end is coupled to ground via a capacitive coupling, allowing High frequency noise to bleed to ground, but no DC current to flow.
The big difference between Profibus and typical DeltaV instrumentation is that PRofibus deals with higher frequencies (up to 12MBit, max 1.5 MBit with DeltaV). At this requency, distance of cables is 100 m. Typical instrumentation is 1200Baud for HART and 31.5KBaud for FF. The shield cable on Profibus cabel is a heavier duty braided shield, not a foil with drain wire. So we are dealing with different requirements.
The update in BOL provided by Jim shows that the DeltaV terminal block provides three terminals connected together so you can connect shields together and ground them using these three terminals. HOwever, if you follow Profibus install guies, you would ground the shields at the end, where they enter the cabinets, and not at the DeltaV terminals.
I'd go with Profibus installation guide lines for Profibus cables.
Andre Dicaire