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'OT remote monitoring'
1999\01\14@234653 by Pedro Drummond

Hi, folks.

What is the best way to keep track of a 0-24V instrument from a distance of
2 miles (approx. 3 km) ? I have wires from point to point, already. Well, I
have a PLC at the monitoring station, but I guess I can't help but add some
treatment to the signal at the source and then send it digitally. What is
the max. distance for a RS-485 interface ? Am I forgetting something ?

Best wishes,


1999\01\15@082740 by Mark Willis

I think most here would want to know your data rate (i.e. how many
bits of resolution are you reading with, and how often?)  Sounds a LONG
way for RS-485, perhaps current loop (Ick, I know <G>) if slow enough
baud rate here?  Also using a "Leased Line" modem pair would perhaps
work, if you can find good modems for the job (ZyXEL's did it for me,
once.)  What's cheapest, would take more data for an optimized answer


Pedro Drummond wrote:
{Quote hidden}

1999\01\15@090641 by Harrison Cooper

How about short-haul modems?  I think thats what they are...BlackBox makes
some I believe.

1999\01\15@093507 by Mark Willis

Short-haul modems AKA current loop modems <G>  They have limits but
probably are the answer, here, if his data transfer rate's slow enough.


Harrison Cooper wrote:
> How about short-haul modems?  I think thats what they are...BlackBox makes
> some I believe.

1999\01\15@120839 by Pedro Drummond
Yes, well data rate is not a problem, I will need to update the reading once
in a while. So I can send it as slow as I have to.

Do any of you have links to current loop modems ?

Thanks a lot.


At 07:04 15/01/99 -0700, you wrote:
>How about short-haul modems?  I think thats what they are...BlackBox makes
>some I believe.

1999\01\16@023117 by Mark Willis

One pair was on eBay for $25 just yesterday, lessee:,
contact, these didn't sell so I presume he'll re-list
them?  If not, B&B [] usually has
this sort of thing, at semi-reasonable pricing, also Black Box

 B & B Electronics wants about $40 USD apiece for these, see Page 11 of
their catalog (It's downloadable as a .PDF file.)  They also want $15
for the power supply, which you may not want to pay <G> Theirs are
already opto-isolated (You want optoisolation, for a 2-3 km long line!
You knew that already though <G>)  (I'm paranoid, maybe, but I'd have
lightning rods at each end - if appropriate <G>  Mother Nature is pretty

 Black Box: See page 524 of their catalog, the # ME739 series is what I
suspect MIGHT work, but these are transformer isolated not
opto-isolated, and they want $170 apiece for these, so think B & B maybe


Pedro Drummond wrote:
{Quote hidden}

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