# Usage of optical fibre in electrical wiring.

1. May 20, 2010

### sugandh

i have a serious question
for reducing the cables and cost of a machine i want to use optical fibre(OF) ,if we have approx.50 sensors,limit switches ,potenstiometers and vavles solenoids all together in one part of a machine can i convert the output of these to get a signal form or multiplexing it to get a digital form and then converting this to light to travel to the main panel just 20 meters away and vice versa to get electrical signal again to operate PLC ,will it be cost effective??which OF type can i use?can OF takes all the signal in its one light beam?
eliminating copper cables for this number of devices,connectors,relay,junction boxes, trays will reduce but ahat about the cost factor.is it really feasible???

please as fast any one can tell me

2. May 20, 2010

### stevenb

It should be doable and may be cost effective. There are many design details and comparisons to be done if you want to be sure, but a first guess would be that it would be a better way to go. Engineering non-recurring costs may be considerably higher with this approach.

3. May 20, 2010

### dlgoff

I don't think you would be able to save any money going to fiber as a way to eliminate wiring since each of your input/output devices would need to be interfaced to some sort of http://www.ni.com/dataacquisition/" [Broken] in order to get the signals on one data line. Then you would need to take this data and translate it to your PLC requirements; requiring more electronics.

In my opinion, wire is cheap.

Last edited by a moderator: May 4, 2017
4. May 20, 2010

### sugandh

thanks for your replies ,but what about plastic clad silica fibre system,or plastic optical fibre and demultiplexing all signals to one and then transferring thru optical fibre and again regenrating the signals thru it,i have been searching and i got that BMW and MErcedees r using POF(plastic optical fibre) MOST & BYTEflight in cars for cost reduction, ours approach is towards cost reduction coz the manufactured quantity is much higher in a year span and the machines have some what same to automobile. the bigger problem is this that can i go for a high voltage transmission like of motors in the same signal with others like sensors and limit switch signals.it will be short distance of some min.2 to max.10 meters.

5. May 21, 2010

### cjameshuff

As lengths go down, the advantage of optical fiber drops. Fiber is cheap, but the transceivers at each end are not, and their price is the same regardless of length. Assembly of fiber is also more difficult, and it is a poorer fit to a bus topology with many devices attached to a common bus. Instead of one cable running around to each device, you have a cable to a hub and many cables going to that hub from each device, or two transceivers on each device allowing them to be chained together, and electronics for passing messages through to the other side.

For relatively long runs between clusters of devices, fiber has an advantage for automotives in not producing and being immune to interference, automotives being high-EMI environments. It can also transmit signals between electrically isolated systems without requiring any additional isolation, also something useful in automotive and industrial electronics. I am doubtful about it reducing cost or complexity.

6. May 21, 2010

### stevenb

Keep in mind that a detailed study of the system specs is needed to make a real determination on this question.

Prices on optical communications at this scale has come down quite a bit. I expect a point to point communications is well below $50 now including transmitter, receiver and fiber. To some people that is very expensive, to others it is very cheap. It really depends on your system. If a system sells for$10000, then the benifits of fiber are going to be more important than the cost. If you are mass-producing a system with a \$10 street price, then this additional cost is unacceptable.

7. May 24, 2010

### sugandh

more help for size of optical cable
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)