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PostPosted: Wed Jul 03, 2013 6:36 am 
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Quote:
co2 = co2 * 0.8317 * 44.01 / 10000;
// converts ppmv to ppmw
// quicker than co2/1000000 * 0.8317 * 44.01 / 1000000
// 0.8317 accounts for Henry's Law
// max ppmw will be 36.6 ppmw with 10,000 ppmv


hi mistergreen i followed this thread from TPT. just want to say i admire your work on the DIY parmeter also. now on to the CO2 meter...

the part where i quoted is where i believe the calc error lies. there is already an arithmetic mistake when "co2 * 0.8317 * 44.01 / 10000" is equated to "co2/1000000 * 0.8317 * 44.01 / 1000000"

it should actually be co2*0.8317*44.01/1000 to yield an answer in mg/L (ppm w). note that for 10,000 ppm v, this calculates to
366.01 mg/L (CO2/water). this is where i discovered the second error. using the Henry constant value 0.8317 requires that the gas concentration of solute (CO2) be in mole concentration(mol/L). the problem is that the sensor returns values in the unit of mol ratio(number of CO2 atoms as a fraction of all other gas atoms passing the detector), which is equivalent to ppmv due to Avogadro's Law. to put it simply, you have to take 366.01 and divide it by 24 if we want to use 0.8317 correctly. this due to 1L of gas only having 1/24th a mole of any gas particle (accurately 1/24.4 at 25C). ie, ~24 ppmv CO2 in air is 1/1000000 mol/L CO2 in air.

366/24=15.2 mg/L or ppm w CO2 when the meter is maxed at 10k ppm v. this is in agreement with kkara's calcs.

a convenient constant i would use is CO2(dissolved ppm w) = CO2(ppm v) / 668.5. derivable from the other form of henry's constant 29.41 L*atm/mol and CO2 molar weight 44 g/mol.

of course this poses the problem that what we want is out of range for this sensor. and the highest CO2 log values (saw from the other forum) from your tank (about 18+ ppm w) is overstated by a factor of 2.44 assuming the above quoted code was in use


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PostPosted: Wed Jul 03, 2013 3:13 pm 
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Joined: Thu May 30, 2013 5:25 pm
Posts: 11
gregorian wrote:
Quote:
co2 = co2 * 0.8317 * 44.01 / 10000;
// converts ppmv to ppmw
// quicker than co2/1000000 * 0.8317 * 44.01 / 1000000
// 0.8317 accounts for Henry's Law
// max ppmw will be 36.6 ppmw with 10,000 ppmv


hi mistergreen i followed this thread from TPT. just want to say i admire your work on the DIY parmeter also. now on to the CO2 meter...

the part where i quoted is where i believe the calc error lies. there is already an arithmetic mistake when "co2 * 0.8317 * 44.01 / 10000" is equated to "co2/1000000 * 0.8317 * 44.01 / 1000000"

it should actually be co2*0.8317*44.01/1000 to yield an answer in mg/L (ppm w). note that for 10,000 ppm v, this calculates to
366.01 mg/L (CO2/water). this is where i discovered the second error. using the Henry constant value 0.8317 requires that the gas concentration of solute (CO2) be in mole concentration(mol/L). the problem is that the sensor returns values in the unit of mol ratio(number of CO2 atoms as a fraction of all other gas atoms passing the detector), which is equivalent to ppmv due to Avogadro's Law. to put it simply, you have to take 366.01 and divide it by 24 if we want to use 0.8317 correctly. this due to 1L of gas only having 1/24th a mole of any gas particle (accurately 1/24.4 at 25C). ie, ~24 ppmv CO2 in air is 1/1000000 mol/L CO2 in air.

366/24=15.2 mg/L or ppm w CO2 when the meter is maxed at 10k ppm v. this is in agreement with kkara's calcs.

a convenient constant i would use is CO2(dissolved ppm w) = CO2(ppm v) / 668.5. derivable from the other form of henry's constant 29.41 L*atm/mol and CO2 molar weight 44 g/mol.

of course this poses the problem that what we want is out of range for this sensor. and the highest CO2 log values (saw from the other forum) from your tank (about 18+ ppm w) is overstated by a factor of 2.44 assuming the above quoted code was in use


ah good to know my calcs are inline. I have a 30000ppm sensor on order will see how I go


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PostPosted: Sat Jul 06, 2013 3:10 pm 
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Posts: 275
gregorian wrote:
Quote:
co2 = co2 * 0.8317 * 44.01 / 10000;
// converts ppmv to ppmw
// quicker than co2/1000000 * 0.8317 * 44.01 / 1000000
// 0.8317 accounts for Henry's Law
// max ppmw will be 36.6 ppmw with 10,000 ppmv


hi mistergreen i followed this thread from TPT. just want to say i admire your work on the DIY parmeter also. now on to the CO2 meter...

the part where i quoted is where i believe the calc error lies. there is already an arithmetic mistake when "co2 * 0.8317 * 44.01 / 10000" is equated to "co2/1000000 * 0.8317 * 44.01 / 1000000"

it should actually be co2*0.8317*44.01/1000 to yield an answer in mg/L (ppm w). note that for 10,000 ppm v, this calculates to
366.01 mg/L (CO2/water). this is where i discovered the second error. using the Henry constant value 0.8317 requires that the gas concentration of solute (CO2) be in mole concentration(mol/L). the problem is that the sensor returns values in the unit of mol ratio(number of CO2 atoms as a fraction of all other gas atoms passing the detector), which is equivalent to ppmv due to Avogadro's Law. to put it simply, you have to take 366.01 and divide it by 24 if we want to use 0.8317 correctly. this due to 1L of gas only having 1/24th a mole of any gas particle (accurately 1/24.4 at 25C). ie, ~24 ppmv CO2 in air is 1/1000000 mol/L CO2 in air.

366/24=15.2 mg/L or ppm w CO2 when the meter is maxed at 10k ppm v. this is in agreement with kkara's calcs.

a convenient constant i would use is CO2(dissolved ppm w) = CO2(ppm v) / 668.5. derivable from the other form of henry's constant 29.41 L*atm/mol and CO2 molar weight 44 g/mol.

of course this poses the problem that what we want is out of range for this sensor. and the highest CO2 log values (saw from the other forum) from your tank (about 18+ ppm w) is overstated by a factor of 2.44 assuming the above quoted code was in use

Thanks, I'll correct the code to see.



Sent from my iPad using Tapatalk HD


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PostPosted: Sat Jul 06, 2013 3:53 pm 
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Hmm, 366/24 =15.25
So my tank really has 15 ppmw of co2. This low value makes sense since my 30k sensor broke, I'm using the 10k. I'm getting black beard algae as a result and the plants hardly pearl. The fish are happy though. My only concern is the fish's health and behavior when the sensor reads 16K+ppmv.

I've taken the co2 controller offline and have been doing it the old fashion way for the past few weeks.


Sent from my iPad using Tapatalk HD


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PostPosted: Fri Oct 18, 2013 3:31 pm 
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Joined: Fri Oct 18, 2013 3:17 pm
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I was researching aquatic CO2 field measurements and noticed this thread. I noticed your screename from TPT. I didn't realize you had your own forum. I skimmed through this thread and thought you may find one of the articles I came across useful; http://www.researchgate.net/publication/227604768_Direct_and_continuous_measurement_of_dissolved_carbon_dioxide_in_freshwater_aquatic_systemsmethod_and_applications/file/79e414fbdca18c2dc5.pdf
They are essentially doing exactly what you have done. They reference the exact hardware, PTFE, design and function. They compare this method to other academic research methods. It may answer some of the question you have had.


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PostPosted: Sun Mar 23, 2014 9:30 am 
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I should have made the casing out of glass, since silicone bonds to it better than acrylic, hence the leak problem.


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PostPosted: Tue Mar 25, 2014 5:28 pm 
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Just found an interesting quote on wiki concerning Henry's law, http://en.wikipedia.org/wiki/Henry's_law .
Quote:
It (Herny's law) also only applies simply for solutions where the solvent does not react chemically with the gas being dissolved. A common example of a gas that does react with the solvent is carbon dioxide, which forms carbonic acid (H2CO3) to a certain degree with water.


Since CO2 reacts with water, Henry's law does not apply?
Maybe that's why the Henry's law math seems off. Some are converted to H2CO3.


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PostPosted: Sun Jun 01, 2014 11:20 am 
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I found a diy under water CO2 sensor much like what Zorfox linked but it uses arduino type constructions. It's more in-depth and detailed. It was has a temperature & humidity sensor which is smart. If the humidity is high, we know we have a leak?

http://www.mbari.org/education/internsh ... ategui.pdf
Cost is around $500-$600, the most expensive being the Teflon AF (amorphous fluoroplastic resin) tube at $300 at biogeneral.com. I'm assuming the teflon tube you buy on ebay for $5 is not the same stuff.
The teflon can be found here as well
http://www.sigmaaldrich.com/catalog/pro ... &region=US


I'll add an attachment in case this link no longer works


Attachments:
Uzcategui.pdf [1.59 MiB]
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PostPosted: Mon Nov 09, 2015 9:57 pm 
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I thought I'd give the CO2 sensor another try. This time, build the casing as water tight as I can and as cheaply as I can. Thanks goodness the CO2 sensor wasn't permanently damaged. I just had to calibrate it using CO2meter's software.

Image
2" pvc plug with cord grip

Image
Inside I had to thin the top off with a router.

Image
Trap adapter for the silicone membrane.

Image
The adapter has a washer inside which I used with the membrane and silicone for safety measure.

Image
The hardware: Arduino, CO2 senseAir K-30 10%, 5v fan, DHT-22 humidity & temperature sensor.
The fan is for circulation, and the humidity sensor is to alert me if it's too high or if a possible leak. The membrane is porous enough for H2O molecule to pass through. If the humidity is too high, I can remove the plug.

Image

Image
The fit was too snug and the board broke in half so I kept it.

Image
Final product. I'm out of the CO2 game but I'll set up a yeast reactor in a bucket to test. I'll send the data to a mysql database online. I'll post the result soon.


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PostPosted: Thu Nov 12, 2015 5:48 pm 
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So here's the result of the logs

Image

I added a 1 liter yeast diffused it a piece of chopstick and circulated with a powerhead in a 5 gallon bucket. I stopped at 60ppmw. It was recording every 7 seconds so I changed the code to record every 10 minutes instead.

CO2 is still climbing. It's at 100ppmw at last check. I pulled out the CO2 to see it tapered out. Who knew DIY CO2 can go that high. I guess it'll keep climbing if nothing consumes it or diffuse it out of the water. I guess shutting off CO2 at night is a good idea.


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