# More help for size of optical cable

1. May 24, 2010

### sugandh

One more question ,is there how can i decide for my fibre cable type, how can i check the bandwith . normally how can i know the sensors (proximity,capacitive,etc.) bitspersecond of sensors and limit switches,so that it will fit the desired optical cable bandwith.
i am in a confusion whther 28-30 input sensors and limit switches will require how many plastic claded silica fibre or POF.
and 2nd can analog signal be feed into plc input after converting it to digital.(eg.potentiometer signal)

2. May 24, 2010

### mgb_phys

Over short lengths the bandwidth of your optical fibre is essentially unlimited, it will depend on the tx/rx on each end.
Upto a few m plastic fibre will handle Gb/s with simple modulation.

3. May 24, 2010

### sugandh

thanks very much
but still for future expansion i will have to think on this prospect,if no. of input devices increase with any added specifications at that time i will have to change my whole cable,so thinking that point of view i asked for the bits per second for the selection of fibre cable.
coz the machine with full specifications also exist and with standard specifications also exist wihch results to increase in devices.

and if u can tell about the second question i asked for.
can analog signal be feed into plc input after converting it to digital.(eg.potentiometer signal)

4. May 24, 2010

### mgb_phys

Until you get to long enough lengths to worry about dispersion, or you need to put terabytes/sec down the fibre with DWDM.
If you have a sinlge fibre point-point then all the data sources are digitized and then combined with some sort of protocol that specifies which source each packet of data is from.
The potentiometer would be digitised by an Analog Digital Converter (ADC) then be sent along the fibre as a digital signal,
You will need some sort of cpu to do this, take a look at arduino.

5. May 24, 2010

### sugandh

ok thanks a lot
i got the idea but i will just want to clearify to u what i am thinking of,
i want to use optical fibre (plastic or plastic claded silica fibre cable) in my machines having 4 parts each parts consist of 20-30 input devices (sensors,LS,potentiometers)taking this to plc and then from plc to motors output.
there is lots of copper cable wiring ,including junction boxes,housings,cable ties,marktubes,time consuming termination and relays.distance of cables will be approx. 4m to max 20m .
i want to reduce time of working using optical fibre if all signals from input devices will be one signal, multiplexing it and transferring it to plc and again convering these to operate plc.so will it be feasible coz i have to also chk that the cost is reduced from old design and not a single penny is increased. i am afraid that the electronics required will be expensive like the connectors for conversion of signal.and the cost of cable i am not able to get anyehere.
machine is too expensive about 250,000 usd to 400,000 usd and manufacturing units are many in a year.
will it be feasible?can u suggest me site where i can get the cost of cable and its parts for this project?

6. May 24, 2010

### mgb_phys

Something like this could be easily used to replace a single directional rs232 output into a plastic fibre for $5 (you need the coresponding LED at the other end - http://ca.digikey.com/1/1/66628-photodiode-fiber-optic-plastic-if-d91.html) You can also get fancy RS232 to single mode fibre for$150-200 from the usual PLC makers.

If you have lots of inputs it might be easier to connect them all to a single micro and then have a single rs232 link over fibre to the main system