HighlandReefer
Team RC
According to Stephen Hawking, if this were really a perfect universe, we would not exist. Something went wrong with the Big Bang. So, does this mean reality doesn't exist? :lol:
Ion-specifc electrode array: control ALL water parameters
- Thread starter Foxy Brown
- Start date
Foxy Brown
New member
My first successes on this project! It's only in lab so far (using artificial seawater) and not in a real tank, as I'm still setting up my new one.
I now have a working phosphate electrode with a detection limit of 0.1ppm! It's based on a simple and cheap piece of cobalt wire.
I also have the final design of the sensor module electronics. Voltages will are converted to digital values for the microcontroller using a Dallas "1-wire" quad analog-to-digital converter (DS2450). Each input is buffered through a precision op-op stage (OPA4376).
It's only interferences are from pH and pO2, so I have added those, and calibrated for their effect... which is a just a small factor multiplied the voltage of the pH and pO2 electrodes and subtracted from the voltage reading on the PO4 electrode. That voltage is then converted to PO4 concentration by comparing it to the reference in the pH electrode and plugging it into a simple linear equation. There's a final adjustment for temperature, and that's it. That makes 4 inputs, utilizing all 4 channels on the ADC, plus an extra 1-wire temp sensor on the same bus. It's all digital after that, so can be arbitrarily far from the PC (or micro-controller in the final version).
It's easy, fast, only requires 3 wires (5V, ground & data) running from my laptop, and cost me a total of 20 bucks (plus the pH and oxygen electrodes, which is in keeping with the spirit of the project because these are desirable on their own anyway). I also plan on running the lights, and switching pumps on an off, all using this very same bus! I have prototypes for those as well (1-wire to 10V analog converter, and SSR drivers all based on "1-wire" 8-port digital switches). The connectors are just regular headphone jacks!
No pics yet cuz its just a pile of soldered bits and wires on a lab bench.
So far so good. If anyone wants instructions on the calibration scheme, just let me know. Next up: Conductivity + ORP. Then in order (and in pairs due to interferences): Ca + Mg, BiCarb + NH4, and NO3 + SO4. Then I'm done, unless something else pops up.
I now have a working phosphate electrode with a detection limit of 0.1ppm! It's based on a simple and cheap piece of cobalt wire.
I also have the final design of the sensor module electronics. Voltages will are converted to digital values for the microcontroller using a Dallas "1-wire" quad analog-to-digital converter (DS2450). Each input is buffered through a precision op-op stage (OPA4376).
It's only interferences are from pH and pO2, so I have added those, and calibrated for their effect... which is a just a small factor multiplied the voltage of the pH and pO2 electrodes and subtracted from the voltage reading on the PO4 electrode. That voltage is then converted to PO4 concentration by comparing it to the reference in the pH electrode and plugging it into a simple linear equation. There's a final adjustment for temperature, and that's it. That makes 4 inputs, utilizing all 4 channels on the ADC, plus an extra 1-wire temp sensor on the same bus. It's all digital after that, so can be arbitrarily far from the PC (or micro-controller in the final version).
It's easy, fast, only requires 3 wires (5V, ground & data) running from my laptop, and cost me a total of 20 bucks (plus the pH and oxygen electrodes, which is in keeping with the spirit of the project because these are desirable on their own anyway). I also plan on running the lights, and switching pumps on an off, all using this very same bus! I have prototypes for those as well (1-wire to 10V analog converter, and SSR drivers all based on "1-wire" 8-port digital switches). The connectors are just regular headphone jacks!
No pics yet cuz its just a pile of soldered bits and wires on a lab bench.
So far so good. If anyone wants instructions on the calibration scheme, just let me know. Next up: Conductivity + ORP. Then in order (and in pairs due to interferences): Ca + Mg, BiCarb + NH4, and NO3 + SO4. Then I'm done, unless something else pops up.
Foxy Brown
New member
My first successes on this project! It's only in lab so far (using artificial seawater) and not in a real tank, as I'm still setting up my new one.
I now have a working phosphate electrode with a detection limit of 0.1ppm! It's based on a simple and cheap piece of cobalt wire.
I also have the final design of the sensor module electronics. Voltages will are converted to digital values for the microcontroller using a Dallas "1-wire" quad analog-to-digital converter (DS2450). Each input is buffered through a high-input impedance precision op-op stage (OPA4376).
It's only interferences are from pH and pO2, so I have added those, and calibrated for their effect... which is a just a small factor multiplied the voltage of the pH and pO2 electrodes and subtracted from the voltage reading on the PO4 electrode. That voltage is then converted to PO4 concentration by comparing it to the reference in the pH electrode and plugging it into a simple linear equation. There's a final adjustment for temperature, and that's it. That makes 4 inputs, utilizing all 4 channels on the ADC, plus an extra 1-wire temp sensor on the same bus. It's all digital after that, so can be arbitrarily far from the PC (or micro-controller in the final version).
It's easy, fast, only requires 3 wires (5V, ground & data) running from my laptop, and cost me a total of 20 bucks (plus the pH and oxygen electrodes, which is in keeping with the spirit of the project because these are desirable on their own anyway). I also plan on running the lights, and switching pumps on an off, all using this very same bus! I have prototypes for those as well (1-wire to 10V analog converter, and SSR drivers all based on "1-wire" 8-port digital switches). The connectors are just regular headphone jacks!
No pics yet cuz its just a pile of soldered bits and wires on a lab bench.
So far so good. If anyone wants instructions on the calibration scheme, just let me know. Next up: Conductivity + ORP. Then in order (and in pairs due to interferences): Ca + Mg, BiCarb + NH4, and NO3 + SO4. Then I'm done, unless something else pops up.
I now have a working phosphate electrode with a detection limit of 0.1ppm! It's based on a simple and cheap piece of cobalt wire.
I also have the final design of the sensor module electronics. Voltages will are converted to digital values for the microcontroller using a Dallas "1-wire" quad analog-to-digital converter (DS2450). Each input is buffered through a high-input impedance precision op-op stage (OPA4376).
It's only interferences are from pH and pO2, so I have added those, and calibrated for their effect... which is a just a small factor multiplied the voltage of the pH and pO2 electrodes and subtracted from the voltage reading on the PO4 electrode. That voltage is then converted to PO4 concentration by comparing it to the reference in the pH electrode and plugging it into a simple linear equation. There's a final adjustment for temperature, and that's it. That makes 4 inputs, utilizing all 4 channels on the ADC, plus an extra 1-wire temp sensor on the same bus. It's all digital after that, so can be arbitrarily far from the PC (or micro-controller in the final version).
It's easy, fast, only requires 3 wires (5V, ground & data) running from my laptop, and cost me a total of 20 bucks (plus the pH and oxygen electrodes, which is in keeping with the spirit of the project because these are desirable on their own anyway). I also plan on running the lights, and switching pumps on an off, all using this very same bus! I have prototypes for those as well (1-wire to 10V analog converter, and SSR drivers all based on "1-wire" 8-port digital switches). The connectors are just regular headphone jacks!
No pics yet cuz its just a pile of soldered bits and wires on a lab bench.
So far so good. If anyone wants instructions on the calibration scheme, just let me know. Next up: Conductivity + ORP. Then in order (and in pairs due to interferences): Ca + Mg, BiCarb + NH4, and NO3 + SO4. Then I'm done, unless something else pops up.
Foxy Brown
New member
No idea why the double post happened.
HighlandReefer
Team RC
Congratulations. 
"detection limit of 0.1ppm"
Is this an error or are you going to further refine this down to 0.01 ppm phosphate?
"detection limit of 0.1ppm"
Is this an error or are you going to further refine this down to 0.01 ppm phosphate?
Foxy Brown
New member
Nope, no error - 0.1ppm. That works out to about 1x10-6 M which is pushing the limit for most any ISE... PO4 was never going to be easy. Unfortunately the response begins to level-off below this concentration, so no way to tell what the true number is just - below 0.1 ppm. On the good side, response doesn't reverse, but just levels-off. If it did you would be stuck with a situation like reading "either 0.01 or 1" which would make it completely useless
While adding a membrane and a filling solution like in a typical ISE might help but would probably also decrease conductivity and add noise, and the detection limit would get worse in that case. It would also make it MANY times more expensive.
I'm pretty happy with that result because it's so cheap, and is already comparable with test kits and the popular Hana colorimeter (at the ±0.04ppm error level of these, 0.01ppm means nothing). Plus, this system requires zero effort on the part of the user after calibration, and is a continuous measurement.
I have more work to do to get to an actual error rating, as I haven't had enough time to test it fully. And I need to make multiple electrodes and reference solutions to look at repeatability from one electrode to another and from one calibration to another.
Just my first success, but its encouraging.
While adding a membrane and a filling solution like in a typical ISE might help but would probably also decrease conductivity and add noise, and the detection limit would get worse in that case. It would also make it MANY times more expensive.
I'm pretty happy with that result because it's so cheap, and is already comparable with test kits and the popular Hana colorimeter (at the ±0.04ppm error level of these, 0.01ppm means nothing). Plus, this system requires zero effort on the part of the user after calibration, and is a continuous measurement.
I have more work to do to get to an actual error rating, as I haven't had enough time to test it fully. And I need to make multiple electrodes and reference solutions to look at repeatability from one electrode to another and from one calibration to another.
Just my first success, but its encouraging.
Last edited:
tastydog
New member
I love this thread. Great work Foxy Brown.
I too am building my own system to monitor my reef aquarium but for a different purpose. My goal is not automation but rather controlled testing. I want to see how different foods effect the nitrate of the tank.
I have found a probe that is $13,000 that will continuously measure nitrate in seawater. Of course that is completely unacceptable. I am working to find a way to measure nitrate.
My project so far includes a micro-controller with 3x temperature sensors and a ph probe. I haven't spent the money on conductivity and orp yet. I am waiting to figure out the cheapest but best method.
I have been looking at the alkalinity problem over the past few months too. Because as a secondary mission, I want to monitor parameters like calcium, magnesium and carbonate.
I have this hooked to a custom coded webserver so that I can log data and access it over the net. The controller could easily be adapted to control pumps etc... but that is so trivial that is not the goal of my project.
I have read only half of this thread, I will get through it. However, Foxy Brown, you have my support bud, if there is anything you need help with let me know. If you want someone to try to duplicate you designs and test them, I will. I am going to dig into this until I can measure nitrate and carbonate constantly in my tank.
Brandon
I too am building my own system to monitor my reef aquarium but for a different purpose. My goal is not automation but rather controlled testing. I want to see how different foods effect the nitrate of the tank.
I have found a probe that is $13,000 that will continuously measure nitrate in seawater. Of course that is completely unacceptable. I am working to find a way to measure nitrate.
My project so far includes a micro-controller with 3x temperature sensors and a ph probe. I haven't spent the money on conductivity and orp yet. I am waiting to figure out the cheapest but best method.
I have been looking at the alkalinity problem over the past few months too. Because as a secondary mission, I want to monitor parameters like calcium, magnesium and carbonate.
I have this hooked to a custom coded webserver so that I can log data and access it over the net. The controller could easily be adapted to control pumps etc... but that is so trivial that is not the goal of my project.
I have read only half of this thread, I will get through it. However, Foxy Brown, you have my support bud, if there is anything you need help with let me know. If you want someone to try to duplicate you designs and test them, I will. I am going to dig into this until I can measure nitrate and carbonate constantly in my tank.
Brandon
tastydog
New member
Plato
New member
I apparently am a die hard reefer, feed me more. I can't believe the DialySeas was brought up. I've installed a few, they work. They work too well. The membrane suck out everything good or bad. I'm all about automation. The DialySeas is 4K and Gerry sells them. So Foxy I'll take 10+ even with at 1k to 4k price range. I run a high end aquarium installation and service company. They will sell if it works. I use Ghl profilux controllers now to automate my water changes, dosing, balling, alarms, leaks, or just what ever. You just need your design to talk to a computer like the Ghl such as their Vetch controller module, or a all in one. Nothing better than showing up to a clients house having the ask why are you here. Oh, I got an alarm from you tank. Your temp is too high, looks like bad circuit breaker on the chiller. Customer, hey thanks for saving my tank from frying. I got the alarm and the Profilux let me turn off the metal halides until I could get to his tank and fix the problem. Foxy I applaud your intrigue and determination to stay the course. Keep it up, would be great to see your booth at MACNA one year.
tastydog
New member
I found a nitrate ion selective probe that is fair priced. only 180USD. http://www.vernier.com/til/1432.html
It does have interference from "-Interfering Ions: ClO4-, I-, ClO3-, CN-, BF4-". I am not a chemist so I do not know what that means to me as far as what I else I may have to compensate for. Do any of those 5 pose issues in a reef tank?
The other ideas I am going to pursue are building a UV probe. I have access to some research papers that explain how this is accomplished. It really just comes down to measuring a specific wavelength (220-230nm in this case). The issues arise of course in interference. However, they can be compensated for by measuring other wavelengths and compensating. This is the same concept as what you are trying to do with ion selective membranes. The cool part is, we have just recently learned how to make LED's run in reverse and DETECT light instead of emitting light. Since LED's put off such specific wavelengths of light, if I can find the right wavelengths there could be some really cool possibilities to measure chemistry that we have never been able to before, continuously, in a tank without much cost.
Anyway, I would love an update on your project and I will let you know how my UV/LED experiments go.
Brandon
It does have interference from "-Interfering Ions: ClO4-, I-, ClO3-, CN-, BF4-". I am not a chemist so I do not know what that means to me as far as what I else I may have to compensate for. Do any of those 5 pose issues in a reef tank?
The other ideas I am going to pursue are building a UV probe. I have access to some research papers that explain how this is accomplished. It really just comes down to measuring a specific wavelength (220-230nm in this case). The issues arise of course in interference. However, they can be compensated for by measuring other wavelengths and compensating. This is the same concept as what you are trying to do with ion selective membranes. The cool part is, we have just recently learned how to make LED's run in reverse and DETECT light instead of emitting light. Since LED's put off such specific wavelengths of light, if I can find the right wavelengths there could be some really cool possibilities to measure chemistry that we have never been able to before, continuously, in a tank without much cost.
Anyway, I would love an update on your project and I will let you know how my UV/LED experiments go.
Brandon
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