FF Wiring Distance from High Voltage Source

[Joseph LaFauci]

Question to FF users;

What are the recommendation FF wiring distances from a parallel high voltage source such as 120 or 480VAC so that noise greater that 50mv will not be introduced on to the segment.

[Talon Petty]

Joe

I am going to move this posting over to the FUN area for more visability,

Joe Conklin FF Marketing

[tibor]

Joe,

What about the current?
It is strongly recommended to put fieldbus cables into different cable tray.
If current is below approx. 20A in each cable (not really power leads),
in this case the min. 15cm distance should be enough.
Allways use cable which shielding rate is grater than 95% and care about shielding rules.

Regards,
Tibor Farkas
P+F; Metso agent
Hungary

[rezabejd]

Do you have VFD's? (Variable Frequency Drives). Some caution may be warranted. I recall a thread on one of the ISA list servers; someone had huge noise issues with H1 & no one could believe it. Turns out the user had some VFD's w/ poorly shielded cables.

We have a few VFD's but have seen no noise issues. There's about 2 M between parallel trays, at least. Have had 70-odd H1 segments running for almost 5 years. Most problems (none extremely serious) have been traced to sub-standard terminations, water logged and / or corroded terminations, or in some cases a funky device.

If you can find the post by Dick Caro on ISA, he describes how the S50 developers abused H1, running in some extremely high noise environments. I looked arond here a bit http://www.isa.org/scripts/lyris.pl?site=isa&page=topic&topic=technology_discussion_lists&text_mode=&lang=english but I couldn't find it . . . The gist of it is, they tried really hard to break it, but couldn't.

Rgds
John Rezabek
BP Amoco Chemicals

[ajith]

Sir

i am new to this FF.I have not worked on this FF.please do send me the basics of FF .how will the wiring and all done in FF instruments.I am adesign engineer .I am presently going to work on FF ,

please do the needful.

[sheusel]

Dear ajith,

for basic knowledge please consider reading the "Fieldbus Wiring & installation guide".

Available at http://www.pepperl-fuchs.com/pa/interbtob/05377/index2_e.html

Regards,
Stefan Heusel

[Peter]

Sir

i am new to this FF.I have not worked on this FF.please do send me the basics of FF .how will the wiring and all done in FF instruments.I am adesign engineer .I am presently going to work on FF ,

please do the needful.

Relcom/MTL offers a comprehensive and practical guide (http://www.relcominc.com/). The FF Website also has an excellent application guide for Intrinsically Safe systems.

Peter Inns
Product Specialist, Intrinsic Safety and Fieldbus I/O
MTL Australia

[rezabejd]

I stumbled upon the old posts to which I referred in an earlier message. It was actually a thread from the FUN list while Ian was still managing it.

Is the "old" FUN list archived here somewhere? The thread was called, "[FUN] Fieldbus grounding and noise spikes". Here are a few exceprts. I apologize for the format -- cutting and pasting from ASCII text messages:

"A perspective on the relative noise immunity of H1, qualitatively - not qualitatively.

Before our first H1 installation, we had concerns about the electrical noise immunity of the H1 system because of the digital nature of its signals. We were assured by the experts who had started up many systems that H1 was very noise immune, and that they had never experienced any noise problems with it.

At start-up, we experienced problems in one of the segments (sorry, I don't recall the specific problem other than to remember that it prevented that segment from being useful).

The H1 segment was properly grounded, shielded, etc. We traced down the problem to be electrical noise induced into a H1 segment from a 480 VAC three-phase VFD (variable frequency drive) motor cable. The VFD and the H1 cables were NOT run in conduit, and were within about three feet or so of one another for approximately a five foot run. We could easily confirm the problem, as simply moving the VFD cable farther away from the H1 cable made the problem go away. Because of the layout, moving the VFD cable was not an acceptable long-term solution, so we solved the problem by replacing the standard SO cord VFD cable with a purpose-made shielded VFD cable.

I know that a conventual 4 to 20 mA DC signal would not have had a problem with this level of electrical noise.

My point is not to incite H1, but rather to say that it IS a digital signal and that standard precautions that are in order for H1 as with any digital electrical signalling technology. H1 is certainly more noise-immune than many higher-speed systems, but even with H1 there comes a point where it cries "uncle."

Jim Reizner
Corporate Engineering
The Procter and Gamble Company"

-----Original Message-----
Carl,

I, with the help of some others, have done testing on the impact of
noise on Foundation Fieldbus. One area that you may wish to look at is
VFD drives. It appears that more companies are using tray cable. I
strongly suggest that Teck cable be used for VFD drives (between the
motors and the controllers). And ensure that the armour is properly
grounded at both ends.

For our testing, the Foundation Fieldbus cable used was Type A with 4
pair individual shield with overall shield. During this testing, only
one pair was used with that pair shield properly grounded at one end.
There was no difference even with connecting the three unused pairs and
shields all together and grounding that at one end. Was also able to
generate sufficient noise by having a "poor" ground for the teck armour.
To mimic field conditions, we had approx 50 meters of cable in various
configurations.

In both cases, the noise seen was very disruptive on the Fieldbus
communications. Even with an air separation of 12 inches (to simulate
spacing in a cable tray) between the tray or poorly grounded tech and
the Type A Foundation Fieldbus cable, the communications was disrupted.
Using harmonic filters and toroid coils did not help.

Our testing also showed that there was no impact due to noise from
zero-crossing controllers (e.g.: high pressure sodium lamps, electric
heat tracing controllers)with the power running in tray cable and the
Type A Foundation Fieldbus cable used.

All other testing did not produce any noise that caused problems.

I would also suggest checking the grounding. I am not sure what your
field wiring looks like (field junction boxes ... surge suppressors ...
local ground ... blocks used) but it may be possible that noise is
entering in from ground in the field. With more details, I may be able
to offer a few suggestions.

I have seen much documentation on the types of wire to use for
Foundation Fieldbus, how to calculate the loading, lift-off voltage,
details of the communications ... but nothing on practical wiring
guidelines for refinery wiring (homeruns, spurs) and recommended wiring
techniques to avoid the problem that you are having. Has anyone ever
seen any publications of this nature?

Glenn