For an R/O system you want something with a sensitivity to reliably know
when you get below 200 ppm. Hanna makes a series of TDS meters that you can
find at many aquarium supply sites. The HI9833318 is a $185 high range
panel mount meter. With an HI7634-00 probe remote sensor it has a range
from 1 to 2,000 ppm. You can set the relay to trip at any level and it is
sensitive enough for R/O purposes and it comes in 120VAC or 12VDC. I think
the probe is 3/4 NPT so you will probably have to add an adapter to your
product line.

When I was building my system I found the older 983319 in an aquarium supply
site. Talked to the Hanna engineers who recommended the 120V model over the
12V model because voltage fluctuations could cause reading errors. The
983318 is the new model and even if they haven't figured out the voltage
errors it would be a simple matter to put a $20 buck/boost regulator on the
supply line.

Since I put up a picture of my panel on the web site I have seen several of
the pro systems add the same model.

BTW, for a really nice looking panel check out
http://www.frontpanelexpress.com/. High quality reasonably priced
professional looking custom aluminum panels and free software to design it
with. Delivery in 2 weeks or less.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Geoff Schultz" wrote in message
.. .
I'm in the process of building a new control panel for my watermaker.
While I'm at it I want to replace the kludged Total Disolved Solids (TDS)
meter setup that I have. Right now I have a portable TDS meter stick that
is epoxied into a block of aluminum that I milled out with a cavity for
the
meter probes and threaded holes for the in/out water.

When I checking the meter, I saw that it had some water intrusion,
probably
from water working up through the prongs in the base of the tester. I
also
have no way to clean the probes, so I'm looking for a better solution.

Does anyone have a source for a (panel mountable) TDS meter that's either
12V or battery powered?

-- Geoff
www.GeoffSchultz.org