rs232/485 -> current loop - off-shelf solution? 2

[ipupkin]

In a coal mine, two devices are communicating at 4,8kbaud over two-wire rs485 bus. There's lot of noise (with a lot of lost bytes), because the power cables from AC-drives lay near, and there's not really a way to avoid it.

Unfortunately, I can't improve "communication skills" of devices (better cyclic codes and so on), they are third-party.

I think, a current loop (with relative high current) would be a robust solution in order to reduce the number of lost bytes. Are there some Ex-certified industrial current loop transcievers available?

 

[IRstuff]

two-wire RS-485 should be run over shielded twisted-pair.

You would need to do the same with your current loop anyway.

TTFN

 

[itsmoked]

I'm not sure you could reach that kind of baud rate on a 4-20mA line. Or are you considering changing from digital to actual 4-20mA analog output modes for your instruments?

 

[ipupkin]

to itsmoked:
I don't mean 4..20mA loop. It's still digital, but 0 and 1 become, for example, -100mA and +100mA. When properly shielded and grounded (thanks IRstuff), it's more noise-proof.

Are there some transcievers available on the market? (It's not really sophisticated - some MOSFET keys, some op-amps... But it's for industry, must be something standard)

 

[analogkid2digitalman]

How about RS-485 to fiber optic converters? That should be fairly tolerant of noise. But I do not know it a COTS solution exists.

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[analogkid2digitalman]

Viola, COTS RS485 to FO converters exist. Of course, you would have to pull fiber if interested in this approach. You did not say how long the run was though. Here's a couple:

http://www.telebyteusa.com/catalog/products/276.htm

http://www.tccomm.com/TC1530.htm

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[itsmoked]

That idea of analogkid2digitalman would definitely be the best approach. Switching 100ma at those rates, down those wires... ugh. And I mean that from a EX point of view too.

 

[richs]

Please let us know your research on the COTS
fiber optics. No need for all of us to do the
same research again.......

Cheers,

Rich S.

 

[subtech]

Hello ipupkin

We use rs-485 in high voltage switchgear and in our switchyards etc. Some twisted pair and some down the "glass tube". A ton of really good info that is free to download concerning rs-232, 422, 485 etc is available here:

http://www.bb-elec.com.

If your mind is made up about the current loop, I'm sure the folks at the above mentioned website can steer you in the right direction. They have helped us several times in the past and made life much easier.
Some of our twisted pair is in switchgears and switchyards near bus at up to 69KV and currents over 1000 amps/phase. It can be done.
Regards
Mike

 

[itsmoked]

http://www.bb-elec.com

*IS* a really got-it-together company with good products.

 

[ScottyUK]

Check out Westermo and Hirschmann for similar products. Both have a decent range of industrial datacomms equipment.

http://www.hirschmann.com/default.cfm?curr_content=s_99&curr_navi=s_99

https://www.westermo.com/Resource.phx/content/uk/index.htx

----------------------------------

If we learn from our mistakes,
I'm getting a great education!

 

[RodVito]

GE Multilin sells an industrial quality RS465-Fibre convertor called Multinet. It will do the conversion you need, and enables you to daisy chain up to 32 devices on the system.

http://www.geindustrial.com/cwc/products?pnlid=6&id=multilink

Rod Lechelt

 

[cbarn24050]

hi, 20mA rs232 was the norm 20 years ago, sould work fine for your app. A modem solution is maybe be easier.