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 Post subject: CO2 sensor!
PostPosted: Wed Dec 12, 2012 10:34 pm 
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So I stumbled upon this CO2 sensor manufacturer by googling.
I wrote to them explaining our hobby and we could use a sensitive sensor to turn on and off our CO2. I got a reply from them. See if this could work out. My main concern is the error range.

It uses infrared to read CO2 in the atmosphere unlike the less reliable chemical reaction sensors we're used too.

Quote:
Thanks for the interest and inquiry.
We measure the concentration of CO2 in water for example by measure the head space gas.
This make use of Henrys gas law regarding concentration in air and liquid.
The measurement are made via a space cup or a gas permeable membrane.
You could do this using a simple k30 sensor;
http://www.co2meter.com/collections/co2-sensors/products/k-30-co2-sensor-module
I’m not familiar with the operation of aquarium but 30 PPM of CO2 in water sounds extremely low for water standing a state of equilibrium.

Regards,


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 Post subject: Re: CO2 sensor!
PostPosted: Wed Dec 12, 2012 10:35 pm 
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I'll stuff it in a breather bag to test things out. I'll think about the design of the enclosure later.

Here's a link on how to interface it with the arduino via UART
http://www.co2meters.com/Documentation/AppNotes/AN126-K3x-sensor-arduino-uart.pdf

via I2C
http://cdn.shopify.com/s/files/1/0019/5 ... 1264294173

I'll have to make a bunch of Close enough par sensors first before I get to this.


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 Post subject: Re: CO2 sensor!
PostPosted: Wed Dec 12, 2012 10:35 pm 
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The sensor arrived.
Image
Cost: $75 shipped

Will have to get some breather bags.


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 Post subject: Re: CO2 sensor!
PostPosted: Wed Dec 12, 2012 10:36 pm 
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Things look good for a bit!

Image
1701ppm outside water

Image

I didn't see any noticeable leak so I went ahead with the experiment
Image

It took a few minutes but the ppm started dropping. It dropped 1 ppm every 2-3 seconds. This is totally responsive in an aquarium where we're looking at 9ppm - 50ppm max. The ppm is a lot more stable in the container compared to air. There was a 2-3 ppm deviation sometimes.

I wanted to see where it would wind up but the readings stopped and notice there was a little water. The experiment ended at 1648ppm. I'm drying things out now. Hopefully there's no permanent damage. I'll need more silicone and thicker band next time.


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 Post subject: Re: CO2 sensor!
PostPosted: Wed Dec 12, 2012 10:38 pm 
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Converting ppmv to ppmw


ppmw = (ppmv)(MW) / [(0.08205) (¦K)] / density of Water


where:
ppmv = air pollutant concentration, in parts per million by volume
mg/m3 = milligrams of pollutant per cubic meter of air - (ppmv)(MW) / [(0.08205) (¦K)]
¦K = atmospheric temperature in degrees Kelvin = 273.15 + ¦C
0.08205 = universal gas law constant in (atm+liter)/(gmol+¦K)
MW = molecular weight of the air pollutant (dimensionless) - mol weight of CO2 (44.01g/mol)
1000 kg/m^3 (density of water)


density of Water = 1000 (kg/m3) - use 1000 as default since you'll need to measure the density to get accurate numbers. The density does vary due to temperature but very minor.

400ppmv of CO2 = .720ppmw


Last edited by mistergreen on Mon Nov 14, 2016 9:16 pm, edited 2 times in total.
Update formula


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 Post subject: Re: CO2 sensor!
PostPosted: Wed Dec 12, 2012 10:39 pm 
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Well, things look good.

I found a little box with clasps at Michael's.
Image
I built a little container within it out of acrylic sheets and silicon glue. The lip has silicon on it so it'll make a good seal with the membrane.

The top is the lid with a home made gasket make out of silicone.
Image

Everything assembled with silicone for extra measure.
Image

It is leak free.

So then it got dunked into my high tech tank.

It rose at about 1ppmw per minute. Final reading was 44.01 ppmw in my tank. It took 30 minutes to get there from 6 ppmw.

All in all a successful experiment. I have ideas on making it even more responsive. Adding more holes in the lid might help and I made a thin sheet of silicone I will replace the breather bag.

So now the next step if to hook this up to a relay to control the solenoid.


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 Post subject: Re: CO2 sensor!
PostPosted: Wed Dec 12, 2012 10:41 pm 
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ok, just finished the app made with Processing. I modified an app I wrote for the PAR sensor. I will run it tomorrow morning. I'll have it log every hour to a text file instead of every second which the CO2 sensor sends to the output pins.

For fun, I ran the app. The lights are off in my low-tech.

There's a time stamp (h:m:s) with the co2 ppm.

log.txt
Quote:

19:7:47 -

Serial Up!

19:7:47 -
Co2 ppm = 10.01

20:0:0 -
Co2 ppm = 11.05

21:0:1 -
Co2 ppm = 12.16

22:0:0 -
Co2 ppm = 12.88



Looks like the trend is the CO2 builds up till the lights turn on. Who knew there was a natural CO2 generator in my tank :).... Actually, I knew.

I let the log app running all day. Here are the results.
Lights on at 9:35:0
Lights off at 17:35:0

Quote:
9:24:59 -
Co2 ppm = 18.70

10:0:0 -
Co2 ppm = 18.64

11:0:0 -
Co2 ppm = 18.03

12:0:0 -
Co2 ppm = 17.48

13:0:1 -
Co2 ppm = 16.76

14:0:0 -
Co2 ppm = 16.22

15:0:1 -
Co2 ppm = 15.81

16:0:1 -
Co2 ppm = 15.61

17:0:0 -
Co2 ppm = 15.43

18:0:0 -
Co2 ppm = 15.33

19:0:1 -
Co2 ppm = 15.61

20:0:0 -
Co2 ppm = 16.01



CO2 fluctuates with the lights. Pretty interesting. The swing is minimal so I'll use that as a model for the hi-tech tank. CO2 turns off at say 40ppm and back on at 35ppm. I'll probably wear out the solenoid with the constant switching. Peak CO2 should be when the lights are on also like the low tech, maybe that's the secret to BBA.


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 Post subject: Re: CO2 sensor!
PostPosted: Wed Dec 12, 2012 10:42 pm 
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I made my own silicone membrane between 2 pieces of wax paper.
Image

It's 1 mm in thickness about 3x as thick as the breather bag. It's also twice as reactive allowing about 2ppm per minute.

I also finished building the relay connections and will hook it up later today. I'll run for a month and observe fish reaction and BBa.

** oh, I just figured there's a mathematical limit to this sensor. You can only read 0 - 44.01 ppmw (this is what we want) and 0 -10,000 ppmv. It's good for growing plants. I probably had higher CO2 levels in my tank. I thought it looked suspicious that it stopped at 44.01ppm every time. I knew there's a reason why my fishes were so skittish.


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 Post subject: Re: CO2 sensor!
PostPosted: Wed Dec 12, 2012 10:42 pm 
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I tried making it thinner but it was impossible remove in one piece. Well at least it's better than the breather bag. I also have a big sheet of vytek. I'll try that later. Making the silicone membrane was easy. A glob of silicone between wax paper and a rolling pin or in my case a wine bottle. Let cure for a few days and peel slowly of one piece and then let it cure completely.

I just did some equipment check and was trying to figure out why the relay wouldn't trigger the solenoid. It turned out the water still had 44+ppm of co2 in it. This is 6 hours after lights out.

I'm going to stay with ranges of 35- 40 ppm. My fishes just aren't happy with the amount I've been pumping in and BBa isn't completely eliminated. I've put the sensor farthest from the outtake so some area will be more than 40 ppm I'm sure.

Can you imagine the amount of co2 we're pumping into these tanks? Over 33x the amount in air.

I'll check the co2 sensor manufacturer if they make something higher than 10,000 ppmv.
**** they do make a 30,000ppm and a 300,0000 ppm model but they're $250.

The 30,000 module should work. The maximum value is 132 ppmw.


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 Post subject: Re: CO2 sensor!
PostPosted: Wed Dec 12, 2012 10:43 pm 
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Posts: 275
Ok, I bit the bullet and bought .010" silicone from http://www.sspinc.com/ssp_store/Thin_Silicone_membranes_from_002_thick_to_040_21.htm

I could have gone thinner but I'm afraid it might be too fragile.
We'll see.


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