OK guys - heres the scoop. There isn't anything on the market that I know of that can monitor and control the water quality in a spa.
PH probe
Alkalinity measurment
Bromine/Chlorine measurment

Being a discrete guy some of the chemistry is forgien like me but..
wondering if anyone has a similar interest, or have done any homework on these 'probes' I think the result could be markatable in some way - maybe for charity, but the cost of the complete system should be in the 200-300 dollar area CDN.

Am I really crazy? Thx in advance.


Cheers from:

Jeremy Pollard, CET
The Crazy Canuckian!
Integration, Automation, and Training

On The Web - http://www.tsuonline.com
PLCopen North America - [email protected] www.PLCopen.org

8 Vine Crescent, Barrie, Ontario L4N 2B3
705.739.7155

 

Well, Jeremy, there are lots of "swimming pool and spa" controllers on the market.

They generally consist of an ORP cell, a pH cell, and an optional conductivity cell. The ORP cell is used to control the chlorine or bromine feed, the pH and/or conductivity cell are used to control dissolved solids concentration and alkalinity.

It works very much like a cooling tower controller, or a boiler blowdown controller, and in fact, the same devices are often used, repackaged and cheaper.

They require maintenance, which leaves them out of the loop for home hot tubs. Commercial hot tubs are generally easier to care for manually.

Stranco (now part of US Filter) got their start as a manufacturer by making the Strantrol swimming pool and spa controller.

What you can't believe is how inexpensive some of these devices are, in comparison to the prices industrial wet chemistry sensors cost.

Walt Boyes

---------SPITZER AND BOYES, LLC-------------
"Consulting from the engineer
to the distribution channel"
www.spitzerandboyes.com
[email protected]
21118 SE 278th Place
Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
fax:801-749-7142
--------------------------------------------

 

Actually, the home aquarium market (fish) already has such a thing. There are several brands. One high-end ($$$) example is at
"http://www.casco-group.com/Aquadyne.html":http://www.casco-group.com/Aquadyne.html .

As for the probes, check out the Omega pH catalogue. It lays out the scaling and temperature compensation, but you may want to dig up "Instrumentation for Process Measurement and Control" by Norman Anderson to get the math.

Also, be cautioned that simply hooking a pH probe up to a voltage meter will probably destroy it unless you use a unity gain op-amp for impedance matching at >10Mohm. A pH probe acts like a miniature battery using ion
transfer through a specially doped glass (and high impedance) to generate a mV signal. I don't know anything about the alkalinity or bromine/cholorine probes, but I suspect they operate on a similar principle.

The other trouble with the whole scheme is that because of the ion transfer, the probes become exhausted and need to be replace. They also
need to be replace if they become fouled (bacteria/algae/scum/etc.) This means calibration of the circuit to a know solution with each new probe.

As a last thought, at one point I had an electronic circuits cookbook (which was loaned out and never returned) that contained several circuits for pH meters. They basically were pH to voltage converters with pots for scaling and offset and some op-amps to do the exponent and impedance matching. Also check-out

"http://www.thekrib.com/Plants/CO2/hurley-co2-comments.html":http://www.thekrib.com/Plants/CO2/hurley-co2-comments.html . The CO2 controller they are talking about is actually a pH controller since CO2 disolved in water results in carbonic acid, which affects the pH.


Anthony Kerstens P.Eng.

 

Further to A. Kersten's comments:

The Cookbook Anthony referred to may be:

"CMOS Cookbook"
by Don Lancaster
published by Howard. W Sams & Co., Inc.
ISBN 0-672-21398-2

An earlier reference was:
"Solid-State pH Meter"
Popular Electronics
November Issue, 1968

Regards,
Phil Corso, PE
(Boca Raton, FL)

 

One correction. The impedance matching required for the pH probe is 100 mega-ohm.

Anthony Kerstens P.Eng.

 

Thx Walt, and to all of the other respondents. Chemical bacground being what it is, I was unfamiliar with some of the issues. I was unable to track down low cost stuff - now I have better ammunition to get there!! Thx to all.

PS The local spa guys have no knowledge of auto controllers...... seemed to me if they didnt then either Canada doesn't import them or they didnt exist. North of the 49th - a very strange brew indeed.

Cheers from:

Jeremy Pollard, CET
The Crazy Canuckian!
Integration, Automation, and Training

On The Web - http://www.tsuonline.com
PLCopen North America - [email protected] www.PLCopen.org

8 Vine Crescent, Barrie, Ontario L4N 2B3
705.739.7155