[GreenKeys] A reliable current-loop-to-RS232 converter

[Bob Camp]

Hi

The whole 20 / 60 ma loop thing goes back to telephone signaling. These
converters are designed to send computer data over telephone wiring at 
a level that wire plant can accept. The fact that what we call a “60 ma current loop” 
and what they call by the same name goes back to their common ancestry. 
Once you get past a few hundred feet, you need *something* to move data. 
There’s a lot of evidence that current loop can send data more than a few hundred
feet. That makes it a popular choice when you need to run a screen in building A
off of the mainframe in Building C while routing it all through building B. 

Bob

> On Aug 13, 2015, at 10:25 PM, Jeffrey D Angus <jdangus at att.net> wrote:
> 
> On 8/13/2015 9:15 PM, Gil Smith wrote:
>> Shhesh.  Really nothing to go on unless someone recognizes this unit.
>> Likely some Chinese thing in many stores.  I would open it up and
>> trace out the schematic, but that is often not an easy task, especially
>> if it has more than two layers (though I doubt it does).
>> 
>> Does this look familiar to anybody?
> This one in particular no, but I've seen similar.
> 
> The problem is NONE of these are designed to work with an inductive
> load. They are designed to run either a 20 or 60 mA current loop using
> a matching converter at both ends of the cable.
> 
> The "give away" on any of these converters is the "Will work up to 19K
> baud." That and being powered off a USB cable or external +5v supply.
> 
> Similar problems with the "Black Box Inc." current loop converters."
> They were designed with a maximum loop voltage of around 65 vdc, 
> NOT 120 vdc. And they get unhappy REALLY fast driving a 4 Hy magnet
> with huge spikes from the switching.
> 
> 
> 
> 
> 
> -- 
> Jeff-1.0
> wa6fwi
> 
> http://www.foxsmercantile.com
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