Foxy Brown
06/12/2010, 08:59 AM
Hi all, I've been working slowly on a long term project to build a system to measure water parameters, and to link the measurement to a computer controlled dosing rig. The trick is: I don't want to just measure pH, or ORP but EVERYTHING. Before I start, I do hold graduate degrees in both chemistry and engineering, so I know a thing or two on the subject. It's mostly practical fish-keeping experience I lack the most, as I'm still relatively new.
Here's the idea: We ALL need to measure some basic parameters, and there are others we would all like.
Good: pH, ORP, Salinity (conductivity) Alk (CO3), Hardness (Ca)
Better: Good + NH4, PO4, Mg
Best: Better + Trace elements (I, Sr, etc.)
You can measure all of these with ion-specific electrodes BUT there are usually errors. These errors are due to cross-sensitivity (NH3 with K or NO3 with Cl for example) That tends to limit the accuracy.
What I've been working on is, to pair-up these electrodes so that each pair would measure both the desired ion and its interfering partner. So here's how you start:
First you make a reference electrode (Ag wire coated in AgCl - very easy to make). Then add ORP electrode (Gold or platinum wire) and measure the voltage between the 2 electrodes to have ORP. Same thing for a glass pH electrode. Conductivity is also easy and all 3 above are commercially available.
Now for the ion-specific electrodes, you coat a silver wire with a special solution of PVC containing a few additives (called ionophores - also commercially available), and you measure the voltage vs the REF electrode. You must measure them in pairs though and you can use a simple equation to calculate the concentration of BOTH. The pairs are: (Mg + Ca, NH4 + K, NO3 + I, PO3 + SO4) and then add 1 for HCO3.
Sounds like alot of electrodes yes, but they are only tiny coated wires and when done, you can control ALL water parameters. Conductivity = dose DI water / concentrated salt solution, pH = dose HBO3/NaB4O7 or H2SO4/Na2SO4, ORP = dose ascorbic acid (Vitamin C) / ozone, Mg = dose MgSO4, Ca = dose CaCl2, Alk = dose NaHCO3, NO3 or PO4 = turn on a reactor (Zeolite/GFO) or dose vodka if you prefer, etc... you get the idea.
The interface is easy, you just need to build some FET-input instrumentation amplifiers (easy), hook them to the ADCs of a microcontroller or PLC (very easy), do a bit of programming (less easy but not hard) and use it to turn on dosing pumps. The last step is calibrating everything, which is not a bad as it sounds.
Anyone got any comments or feel like helping out? What I could really use is someone with a good tank to test it on (don't hook-up the pumps, because I don't want to mess with anyone's system), just see if it gets the diagnosis right, and gives the correct response. That, and maybe someone with more programming experience than I have.
Here's the idea: We ALL need to measure some basic parameters, and there are others we would all like.
Good: pH, ORP, Salinity (conductivity) Alk (CO3), Hardness (Ca)
Better: Good + NH4, PO4, Mg
Best: Better + Trace elements (I, Sr, etc.)
You can measure all of these with ion-specific electrodes BUT there are usually errors. These errors are due to cross-sensitivity (NH3 with K or NO3 with Cl for example) That tends to limit the accuracy.
What I've been working on is, to pair-up these electrodes so that each pair would measure both the desired ion and its interfering partner. So here's how you start:
First you make a reference electrode (Ag wire coated in AgCl - very easy to make). Then add ORP electrode (Gold or platinum wire) and measure the voltage between the 2 electrodes to have ORP. Same thing for a glass pH electrode. Conductivity is also easy and all 3 above are commercially available.
Now for the ion-specific electrodes, you coat a silver wire with a special solution of PVC containing a few additives (called ionophores - also commercially available), and you measure the voltage vs the REF electrode. You must measure them in pairs though and you can use a simple equation to calculate the concentration of BOTH. The pairs are: (Mg + Ca, NH4 + K, NO3 + I, PO3 + SO4) and then add 1 for HCO3.
Sounds like alot of electrodes yes, but they are only tiny coated wires and when done, you can control ALL water parameters. Conductivity = dose DI water / concentrated salt solution, pH = dose HBO3/NaB4O7 or H2SO4/Na2SO4, ORP = dose ascorbic acid (Vitamin C) / ozone, Mg = dose MgSO4, Ca = dose CaCl2, Alk = dose NaHCO3, NO3 or PO4 = turn on a reactor (Zeolite/GFO) or dose vodka if you prefer, etc... you get the idea.
The interface is easy, you just need to build some FET-input instrumentation amplifiers (easy), hook them to the ADCs of a microcontroller or PLC (very easy), do a bit of programming (less easy but not hard) and use it to turn on dosing pumps. The last step is calibrating everything, which is not a bad as it sounds.
Anyone got any comments or feel like helping out? What I could really use is someone with a good tank to test it on (don't hook-up the pumps, because I don't want to mess with anyone's system), just see if it gets the diagnosis right, and gives the correct response. That, and maybe someone with more programming experience than I have.