[GreenKeys] RS-232 / Current Loop converter inquiry

[drlegendre .]

While I'd been planning to DIY one of these units, I came across a deal
that was just a little too cheap to pass up. I picked up a pair of
commercial RS-232 / CL converters on eBay - for reference, a couple of pics
can be seen here:

http://nerp.net/~legendre/greenkeys/rs232_cl_converter_01.jpg
http://nerp.net/~legendre/greenkeys/rs232_cl_converter_02.jpg

(Quick FYI: From this point forward, all greenkeys-relevant files I serve
can be found at nerp.net/~legendre/greenkeys)

First question - does anyone have documentation for this particular 'Model
V' device? I'm not sure who actually made it, as one or two obvious
re-brands can be found here, there and on eBay. It must be self-powered and
probably capable of supplying loop current, with the AC mains connector and
all - so I'd think there'd be a provision to switch the current sources on
or off for each Tx / Rx loop.

Secondly, since I don't presently own any equipment with a current-loop
interface, I need some other method for testing these hardwares. Is it as
simple as tying the CL ports together, matching Tx to Rx and so forth?
Obviously, both adapters could not simultaneously be in the active or
passive modes, thus my first question about toggling those features.

But is there any reason that would not work, as a test setup? A standard
RS-232 terminal on each end, with two 24ga copper pairs joining the CL
interfaces?

Thanks for your inputs!
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