Data Communications & Computer Networks ??

[baller1]

I would like to introduce myself as a new member of Eng-Tips Forum.
I have been asked a question with a range of multiple choice answers.

Question:

Suppose you were asked to specify the type of transmission medium to be used in a factory containing electrically operated machine tools, which one would you choose and justify your answer.

My first decision was to use guided data transmission, as in wires and fibres as the machines in the factory are all based in the same place rather than at different location.

Option one;
Initially, my thoughts went in the direction of Shielded Twisted Pair (STP), because although relatively expensive, the extra shielding around each twisted pair makes it suitable for noisy environments and less prone to crosstalk than Unshielded Twisted Pair (UTP).

Option two;
My second choice was coaxial cable, which offers a greater bandwidth, better noise immunity, and less crosstalk than UTP.

Option three;
My third choice was to use Fibre-Optics.With a choice between multimode or single-mode fibre.
Transmission with lasers can be ruled out because of inpracticality.We will therefore have to use Light Emitting Diodes (LED’s).

Please can anyone with any experience with Data Communication provide some help???


Regards
Baller1

 

[yayogakk]

noise isn't just the prime factor to consider isn't it?

price, topology and scalability also comes into play, not to mention security too.

you have to weigh your options through these factors in order to really justify your preferred choice.

 

[Pali]

This is an interesting question, however you seem to be phrasing the question in terms of anticipated solutions and technology. Try an alternative approach: phrase the question in terms of the desired results. Specifically, what is it you're transmitting? between what/whom? What are the goals and constraints associated with this transmission? And what is the environment in which you are transmitting (this is already addressed in your question)?

For example, are you hooking computers together that will be speaking TCP/IP? Or are you hooking humans together for voice communication? (The subject seems to address this, but not in its entirety) Is the subject of communication cammands which will drive machinery? If so, are the tolerances such that any error could be devastating? Is the form of communication meant to be confidential i.e., part of the company's market advantage? etc.

This approach may lead you down a different path. But it has a higher likelihood of providing a successful solution to your problem.

 

[DON43]

the transmission medium of choice would have to be fiber
because fiber is carrying a signal that is not related to
motor,transformer,cross talking etc. interferance.
if you have used stp or coax you may have noticed how succeptable they are to improper grounding induced problems
and ground loops and building grounds that are not at the same potential.
this would force you to remove the ground connection from one end of the cable and let it float.(which would be an improper grounding technique)
fiber would give you electrical isolation and since it does not connect two dissimilar ground potentials it is not affected by ground loops or differences in building ground

 

See

http://www.SCADANEWS.COM

Hardware section can help

 

[tomatge]

For what its worth my advice is as follows ...
The choice of media will depend on a number of factors, that you have not specified. For example, the solution may be different if you are connecting PC's together using ethernet, than if you are using serial communcations (e.g. RS-485) to connect to telemetry or control devices.
High bandwidth (e.g. ethernet) through an industrial environment tends to lead towards fibre, and for the distances involved multimode fibre should be adequate. However, you should not underestimate the capability of copper cable (STP), which may well work adequately provided the environment and cable highways are suitable. Provided the communications cable does not run too close and parallel to power cables and plant, it may well be adequate, and will be easier and cheaper to install than fibre.
If you're looking at serial communications (e.g. RS-485) then you will almost certainly find that shielded twisted pair cable will work at moderate bandwidth (say up to 64kbps). I operate such circuits in a power station environment subject to severe interference problems from both High Voltage and Medium Voltage equipment.
Finally, I do not agree with a comment made by DON43 - if he is referring to grounding of the screen, then the correct technique is to direct ground at one end only, to avoid circulating currents. Capacitive grounding may be additionally provided at other points on the circuit.

 

[VxA]

I'm leaning toward multimode fiber. The distances are short enough that the extra money for singlemode fiber (with more expensive lasers, etc.) is not justified. Also fiber is good because there is no electromagnetic interference. To give the true best answer though, more info would be needed.

 

[ElectroKing]

-Use sheilded cable twisted pair (indiidually sheilded and overall foil aorund conductors).
- For Ethernet use CAT5 or better.
- For CAN technology follow the specifications for the cable for layer 7 network.
- Use good open sheild / single ended grounding technique for the overall foil/ sheild.
_ Be Safe