Transmitting linear 4-20mA d.c. signal over fibre optic cable

There has _got_ to be a way to do this with off-the-shelf equipment. I'd web search on "20mA" and "fiber" and see what pops up. Failing that, I'd post on sci.engr.control -- most of that group is experienced industrial control guys, so you'll not only get a reply from someone who knows of a box, you'll get a reply from someone whose used a few different brands and can tell you where the bodies are buried.

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Here's one, probably massive overkill, but cheaper than engineering a new version.

Try "current loop" and "fiber optic" for search terms to find others.

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I assume(?) there is no fiber mux you can get a channel assignment in.

If you must use a whole fiber capacity for the signal channel, look at the Black Box catalog. I recall a RS/EIA 232 to fiber, converter for only a couple hundred $ per end, then you will need a converter to RS232 from

4-20mA for each end. They are likely off-the-shelf too.

You could use a PLC (Programable Logic Controller) at both ends. The input card would be an analog 4-20ma . The other end could be whatever you want to display.

That, or, if you want to make something your self. got out one of those isolator boards and output the signal to a fiber transmitter LED that connects on the end of the fiber.. the other end would use another isolator board that will connect to the output side of the circuit as the receiver..

We use fiber connectors that fit on a PCB's how ever, this will use the whole fiber just for that one job..

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"I\'m never wrong, once i thought i was, but was mistaken"
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Any idea what that costs?

John

I think that one was around 350 or so, Also, that particular unit operates on 220v. it was just an example.

Look at the link near the bottom, they have fiber trunk transmitters/receivers that will except TTL, 485 etc.. I didn't see a 4..20 but with that above, I think you can use a something to adapt.

You know, this isn't rocket science.. Get your self a fiber Transmitter coupler and some fiber on a roll with the prep kit.. make up a PWM to transpose the signal on each end.

I did that just screwing around with something.. It wasn't

4..20 but could be used to transpose what you need. I used a low power fiber transmitter diode coupler with a cheap receiving photo diode coupler at the other end. Something like you fine in audio systems.

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"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

snipped-for-privacy@boltblue.com snipped-for-privacy@boltblue.com posted to sci.electronics.design:

Convert the current loop to digital and transmit that. Check SCADA manufacturers for the equipment.

Thanks, Jamie. That's exactly what I'm looking for.

Strange. A simple application but this product seems thin on the ground. I guess single channel requirements must be relatively rare.

I'll pop over to the control forum to see if anybody knows any equivalents.

Thanks again

Think of it this way: the fiber can carry a huge amount of data - and it's not much harder for it to carry many channels (drive electronics wise) than to carry one - so the default mode is going to be to provide the ability to replace many wire loops with one fiber, where some users might end up with excess capacity, rather than to have single channel devices where a lot of end-user money would have to go to excess fiber if they had more than one wire loop.

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Cats, coffee, chocolate...vices to live by

Well, they might be rare how ever, I used a simple fiber optic transmitter and receiver PCB mounted. PWM modulated the transmitter and then do the simple duty cycle receive at the other end to translate that to a voltage or current in your case. You may want to look into a trunk line transceiver set up. That will allow you to expand later on the different types of information you can convey. I remember making a simple trunk transmitter and receiver years back when I wanted to experiment a bit with it on my own. I used a what I call TWM (Time width modulation). A short pulse would indicate a reset for the string of channels and place the index back to 0. if the pulse past the resync window time, the remainder was used as a time window to generate a 0..100% reference. etc.. I used a PIC chip to do both ends and had the options of digital or ADC output.. 16 channels on that one. only limited with the speed and IO lines I was getting with the old version PIC. today, speed is cheap. :) how ever, It only did one way on each fiber..

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5