using fiber cable to connect plc's 1

[ty626262]

Im working on a job in which i will have several remote i/o racks connecting back to a main plc cabinet. The customer is thinking of using fiber optic cable and daisy chain all the the racks back to the main cabinet. I havent had much experience with using fiber optic cable and im looking for help to see if anyone has some advice. It looks like we will be using multimode cable but i am getting a little confused at the number of pairs i require in the cable for proper communication and which type of cable to use in general. Any help would be appreicated.

 

[djs]

Hello;
Here in Florida we have a lot of lighting. Because of this almost all communications are run via fiber. In recent years the cost of the material has dropped. You can get multimode fiber cable for lees than $0.50 per foot. Fiber modems usually run $500 ea or less.
You need to select the fiber modem according to the type of communications bus you are using. Use profibus modesm for Profibus networks, ControlNet modems for ControlNet networks etc. You can even run Ethernet over fiber.

 

[stephenw22]

Typically, when we connect systems together, it uses either 1 or 2 fiber pairs, depending on redundancy. Each pair will have a Tx and an Rx connection.

Over a short run, you can buy pre-made jumper cables, but if you're going more than a few hundred feet, you'll need to use bulk cable.

If you're installing a long run of cable, you might as well install a 12 or 24 fiber cable, as the cost isn't much more than a 6 fiber cable. I think we paid $1/foot for the last 12-fiber, armored, 62.5/125um multimode cable we installed.

When terminating long runs of fiber, you can use either a mechanical or fused splice in your patch panels. We farm it out to a local telecom contractor who can do the fused connections. They use a little device that actually fuses the connector pigtail onto the bulk cable. It costs us about $1,500 (labour + materials) per 12-fiber end to terminate. The equipment costs about $100,000 if we were to buy what the contractor uses.

 

[pooslinger]

I have fiber connecting my remote racks to 15 different areas of my plant. I recently abandoned the remaining hard wire I/O that was left 4 years ago. All AB PLC 5 and slc 500 racks. They all terminate into a hub that converts the data to Ethernet. My next step I will take on is replacing that hub/converter with a standard ethernet hub and seperate inline fiber to ithernet converters terminating into it. Do not go low bid for price on cable. Some contractors will off there old stock which is obsolete soon after its installed. Not a problem until it has to be spliced ($$$$$). All my runs have an extra pair that is vacant until needed. In my opinion. Until wireless improves, fiber is the only way to network acrossed a facility.

 

[djs]

Hello;
$1,500 per 12 terminations? Where are you located? I want some of that business. Seriously I just finished a job where we installed 100,000 ft of fiber (6 fibers) with the longest run being about 3,000ft. About 240 cables, 480 ends. We used Corning Unicam connectors. Very nice, very quick, and very good. I think our average loss per connector was about 0.1 db.

 

[ty626262]

Thanks for the help guys. A little more information to add. The customer will be using an ethernet switch for an installation similar to the one pooslinger described. It looks like he wants to convert from have ethernet in the i/o's and convert to fiber to transmit between them. The ethernet switch he's looking at using is an 8-port (6-cat5 and 2 fiber). So what im gathering from what you guys have told me is that each pair in a fiber cable is one transmit and one receive. Does that mean for each rack we would need one pair minimum to communicate? Sorry if my questions seem somewhat obvious. I'm really not up to speed on fiber optics and am trying to play catch up.

Thanks again guys for all the help.

 

[ScottyUK]

Yes, one pair is the norm for ethernet comms over fibre.

If it is an industrial environment - hot, cold, damp - then I highly recommend the Westermo range of ethernet equipment. They have some downloadable stuff on their website which you could really benefit from reading to increase your understanding. Hirschmann are another good vendor of hardened ethernet products.

http://www.westermo.com/Resource.phx/content/products/productGroups.htx

http://www.hirschmann-ac.de/English/industrial-ethernet-products/index.phtml

We have set up a fibre network using Westermo's equipment out in the field and a Cisco fibre switch in a clean and controlled environment at the hub of the network. The Cisco allows us to run a 1GB/s uplink to another building which was beyond what Westermo could offer at the time. Prior to this we were using a Black Box 10MB/s fibre concentrator and 10MB/s hubs in the field. Today you shouldn't consider anything lower than 100MB/s and ideally 1GB/s. Fibre is easily capable of this level of performance so build in some future-proofing now.


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Sometimes I only open my mouth to swap feet...

 

[stephenw22]

We were only doing a single run of fiber (around 1500'), and the $1,500 included all the rack-mount panels, fiber connectors, splicing, and testing. With the type of splice the contractor was doing, we were seeing losses of around 0.01dB or less per connector (the splicing machine automatically tested the connection loss). The contractor's standard was that anything over 0.03dB was rejected and re-spliced. It took them about a day to terminate both ends of the fiber and do all of the testing we required.

Our loss over a 3000' loop (there and back, with a jumper on the end panel) averaged 0.3dB, including the losses at the jumper (estimated at 0.1-0.2dB).

 

[ScottyUK]

Forgot to say:

Stephenw22's earlier advice about putting in a trunk fibre is worth listening to. Every day I curse the short-sighted idiot who installed a two-core fibre because he needed... two cores. The cost of the fibre itself was less than 20% of the total installation cost because of the enormous scaffolds required to access the high level routes. Our plant is a diabolical design when it comes to any retrofit work. Putting in a 24 core trunk fibre instead would have added maybe 10% to the job.


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Sometimes I only open my mouth to swap feet...