does anyone who use the fiber use for the rs485 bus in slc500 over 2 miles? should it work? or how do i have to make it work? anyone known where i can get the fiber cable for cheap price.

thanks

 

I'm guessing that you are thinking of a fibre-optic modem with an rs485 port. From what I know, fibre is typically 5dB per km with losses at each junction that depend on the quality of the
joint. If you try to do the installation yourself, and you don't have much practice doing it properly, then don't count on getting
good results.

My non-committal gut feeling is that you will need a repeater somewhere about halfway and you should get a cable installer to properly do the run with welded FO joints to minimize
interface losses.

I **strongly** recommend you get a quote from an installer with demonstrated experience in FO cable.

Anthony Kerstens P.Eng.

 

Generally there are two things very important to consider when extending the communication length: signal damping and transfer time.

The signal damping part can easily be improved by for example the use of fiber, repeaters and so on

The transfer time is quite another matter, the best you can hope for (for now) is that the signal travels with the speed of light, probably somewhat slower.

I do not know if the transfer time is in any way critical in this protocol, I just made this reply as a general statement over increasing comunication distances.

I would guess (but are definitely not sure) that the travel time in a fiber cable actually might be lower than in copper. It have to do with the refractin index, the very part making the fiber cable possible. Repeaters usually add some small
extra amount to the transfer time. For long distances and high speeds more than one bit is on
the cable at the same time (both for copper and fiber), that is right you don't have the same voltage in all parts of a copper cable at the same time and the same amount of light in the entire fiber at the same time, not even theoretical without damping and disturbances.

Again note: the transfer time is not interesting for all protocols and might not be interesting in this particular case. This is a general statement about communication to be considered by them thinking "it works for protocol X and that means it works for protocol Y too" it doesn't work that way!


/Johan Bengtsson

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> Generally there are two things very important to consider
> when extending the communication length: signal damping
> and transfer time.
>
> The signal damping part can easily be improved by for
> example the use of fiber, repeaters and so on
>
> The transfer time is quite another matter, the best you
> can hope for (for now) is that the signal traveles with
> the speed of light, probably somewhat slower.

Common point of confusion this. Light is capable of much higher bandwidth over distance than copper based signals, but this does not have much relevance to signal delays.

Light does not travel in a straight line down the fibre, it bounds around from one side to the other so it always travels a lot further. Also, 3E8 is the speed of light in a vacuum, glass is quite a bit denser.

As for the original question, it is quite easy to send 1Mb over 2 miles without resorting to fibre (which is a lot more expensive than twisted pair, especially considering installation requirements). Unfortunately, allthougth I know this can be done from telecomms experience (T1/E1 connections have mostly been done in copper), products I know of in the IA world tend to fall short of this.

What is your line speed?