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Using Ethernet cable instead of serial cable for 115kbps transmissions

Posted on 2004-11-08
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Howdy all,

I am trying to wire up several Haas CNC machines (very large machines that are used to machine metals and plastics) to a serial server.  The "server" will most likely be a Digi PortServer TS 8:
http://www.digi.com/products/terminalservers/portserverts816.jsp

This device (and other similar devices) has RJ-45 ports to connect serially to your host.  What I need to know is, how long of a cable can I use before the signal degrades at 115kbps speeds?  Also, what type of cable should I get?  Should I go for a high-grade category 6 cable?  A shielded cable versus unshielded?  I have an opinion on this matter, but I'm looking for someone who has either implemented this before and knows the limitations or someone who has actual data to show what is the right stuff to use.

My problem is some of the machines will not be located near the serial server (up to 100' away).  I need to know whether I can do this with one serial server or if I need two.  If I get two, the cables will be around 10' to 30' (no more than 50').

Thanks!

Jeff
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Question by:masterbaker
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by:RyanCh
ID: 12526451
UTP (Unsheilded Twisted Pair) is the basic Cat 5 cable on the market for simple networking, and that has a range of 100M before attenuation causes signal degrading.  In your situation you may want to go with the Cat 6 shielded (depending on how much interference you will be running through) which, while a good bit more expensive, larger, and less flexible will give you better signal over your run.  The short answer is that you really want the cable which is economic for you depending on how much noise you'll encounter.  If you're running near moving parts (motors), TVs or Monitors, or other devices which give off electromagnetic radiation you may want to go for the sheilded cable (or in extreme cases fiber optic, but that doesn't look necessary).

According to Cisco the UTP and STP (unshielded and shielded twisted pair) both have a range of 100m, and bandwidth of 100mbps (although recently several GBps has been achieved over UTP).  So at this point the only question is does your cable need to be shielded because you should be fine with distance.
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by:masterbaker
ID: 12526571
Hi Ryan,

I appreciate your input but the data you presented doesn't apply to my situation.  I know distance and speed limitations for running Ethernet over cat5/6 cabling.  What I need to know are the distance and speed limitations for running serial communications over cat5/6 cabling.  These limitations will not be the same, this I am sure of.

Thanks,

Jeff
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by:RyanCh
ID: 12526758
Ah, sorry bout that.  Lets see here.
Looking at the distance limits of these serial to ethernet converters:  http://www.signamax.de/index.php?typ=SXA&showid=101
I see a 10base T (Which would be the STP or UTP) still h as the 100M maximum, so while the actual distance may varry depending on your specfic hardware, I have a feeling that you should eaisly fall within your distance and speed range.  (on this device it appears to be 10 or 100mbps over 100m).
Looking at the port server TS8/16 which I found over google here:
http://216.239.39.104/search?q=cache:3JuunDbxY8wJ:www.digi.com/pdf/prd_ts_portserverts816.pdf+Digi+PortServer+TS+8+specifications&hl=en&start=1
I noticed:
 230 Kbps throughput on all ports  (so you should at least reach your speed requirements)

Overall I would expect you to be able to get the distance you need off of your server.  There is some contact information in the link I put there if you would like to contact them directly about the distance (however I suspect as long as you aren't facing a lot of interference you should be fine).
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LVL 13

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by:masterbaker
ID: 12526892
I think you're still missing the point.  I'm trying to determine the limitations of the cabling between the CNC machine and the serial server.  This will be using category 5/6 Ethernet cable, but will NOT be running Ethernet.  Another option would be to just use a media converter from the Digi box to go from RJ-45 to 25pin serial and then use a standard serial cable to connect to the CNC machine.  In either case, the speed and distance limitations of Ethernet over UTP/STP do not apply to running serial communications over UTP/STP cabling.  I think that's where the confusion is.

So I want to know the limitations of running serial RS-232 communications over cat5/6 UTP or STP cabling.
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by:gjohnson99
ID: 12526911
If you are using serial you should be able to get 200-300 feet easy. if you need more distance you may want to look at some serial line driver
for distance 1000 feet plus.
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by:RyanCh
ID: 12527021
The limitation of binary information traveling over cat 5/ cat 6 is 100m, it does not matter if it is binary information via serial or fiber optic, or NIC card, once it is put onto the wire with the standard amplitude the limitation of the cable is 100m.  The only thing which would shorten that limitation is if the hardware sending the information ove that cat 5 or cat 6 cable is weaker, but if you have a piece of hardware which is desigend to send the information over ethernet than you will have 100m distance limit.  The distance capabilities of the ethernet cable does not have anything to do with the type of data flowing over it as long as it is properly put on the copper, which you have the devices to do that.  So let me see if the setup I have visualized is right, the machines connect to the server via serial (which isn't the part of the setup we're discussing).  From the server you have an RJ-45 connection to a host.  Your question concerns the distance limits between the serial server and the host.  Let me know if i've got that wrong, because in that situation you'll have up to 100M and you'll need shielded or unshielded depending on your interferece situation.
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by:gjohnson99
ID: 12527091
RyanCh

ethernet distance is limit by the seed it runs  

Why can phone line go so far many 1000s on feet on copper ?
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by:gjohnson99
ID: 12527142
Here is site to look at

http://www.bb-elec.com/tech_articles/serial_communications_systems.asp

Rs-232 100 feet at 115kbps
Rs-422 4000  feet at 115Kbps
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by:masterbaker
ID: 12527183
Actually Ryan, it seems we are discussing different wiring.  I am talking about the wiring between the CNC machine and the serial server.  The serial server is connected to the network with a standard Ethernet connection to the core switch.

As you eluded to, the distance limitation on cat5/6 cabling is based on the strength and type of signal as well as the interference.  Ethernet is designed to go 100m on this cabling.  However, RS-232 serial communications were not designed to go 100m.  They use different signals & protocols.  

Question for you gjohnson99, have you used a serial connection at 115kbps over 200-300 feet?  The CNC manufacturer's spec says to only run 25' at that speed.  We currently have one set up at 75' and it runs fine.  But that's over standard serial cabling.  As you can probably tell, I am trying to make sure this will work before implementing it.  So I'd like a little more data, if possible, to back up the claim.

I'm sorry if I sound picky...  I just would feel more comfortable if I could find a spec or a guide that shows exactly how it will work.

Jeff
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gjohnson99 earned 1000 total points
ID: 12527339
I have run a lot rs-232 stuff a over 200 feet most stuff works fine some will not depends on the equipment. The rs-422 suff work great on poor wiring at great distance.

It yourstuff is rs-232 you can convert it rs-422 the converter are low cost items.

You may want to try the rs-232 if it dose not work convert it rs-422

Your equipmnet may be rs-422 or selectable


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by:masterbaker
ID: 12527464
<To gjohnson99>

When you say you have run rs-232 over 200 feet, is that using standard serial cabling or UTP cabling?

I have thought about RS-422 converters, but I was hoping to avoid that if I could keep the distances reasonable.

I did find another online link that showed distance limitations for rs-232 and it shows 57kbps to max out at under 3 meters!  It seems that if I ran it on cat6 cabling I might be able to get it up to around 10 meters.  That's not even close to what I need.  Oh well, I guess you can't always trust specs.  We're doing 75 feet on serial right now and I know we're not receiving errors.
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by:snerkel
ID: 12527725
I would be inclined to use something like this http://www.bb-europe.com/product.asp?dept%5Fid=125&sku=ESP901 mounted locally to each machine, this will give you an Ethernet link to each machine.

This will give you better redundancy, better noise immunity, easily expandable.
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by:gjohnson99
ID: 12527835
I currenty have stuff running UTP cabling  -  What I am running pc hook to display broad  -  They work fine  

We move to new building about six mounth ago I wanted them to install a stardard serial but they install UTP cabling its been work find.

The distance is largely be dependent on driver chips used and the voltage supplie on your serial devices.



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by:rindi
ID: 12536506
Just another thing to think about,

is it really necessary to use 115kbps? Normally the amount of data sent from servers to CNC machines isn't much and I suspect things would work without problems at much slower speeds, Possibly 9.6 kbps could already be enough?
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by:masterbaker
ID: 12536853
Rindi,

I do need the 115kbps speed.  The serial link is being used to transmit the programs.  They have programs that are several megabytes in size.  They used to use floppy disks (and still do for a couple of the machines).  In the past year though, their more complex designs have gone over 1.44MB so they have needed this link.  They are going to get bigger (they have one around 10MB now) so we definitely need the speed.

Based on the specs I have found, I'm not convinced we can run long distances on UTP (or serial) cabling.  In the interest of preventing data loss or other problems, we are going to purchase a second serial server to keep the cable lengths shorter.

I'm going to award the points to gjohnson99 as his info was the most helpful.

I do have one last question gjohnson99, if you wouldn't mind answering it.  What speed did you run your serial connections at when they went over UTP cabling?  115kbps?  9.6kbps?

Thanks,

Jeff
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