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Old 02-02-2013, 07:55 PM   #21
craigmw
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Instead of counting CO2 bubbles in an airlock, I was referring to using a CO2 sensitive sensor. I saw a nice writeup on the web showing fermentation monitoring using this approach. It would pretty much give you the same info as your airlock setup, so not much of an improvement. There are various ways to measure SG with in-line approaches, including ultrasonic doppler setups, etc. The one I thought was cool was based on a vibrating tube. The idea was to measure the resonance of a small tube filled with the fluid of interest. But, it seems tricky to realize this. Actually, given the delay in various commercial efforts for a cheap setup for home brewers, I guess this turns out to be a pretty hard nut to crack.

 
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Old 02-02-2013, 07:59 PM   #22
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Quote:
Originally Posted by craigmw View Post
Instead of counting CO2 bubbles in an airlock, I was referring to using a CO2 sensitive sensor. I saw a nice writeup on the web showing fermentation monitoring using this approach. It would pretty much give you the same info as your airlock setup, so not much of an improvement. There are various ways to measure SG with in-line approaches, including ultrasonic doppler setups, etc. The one I thought was cool was based on a vibrating tube. The idea was to measure the resonance of a small tube filled with the fluid of interest. But, it seems tricky to realize this. Actually, given the delay in various commercial efforts for a cheap setup for home brewers, I guess this turns out to be a pretty hard nut to crack.
Hmm...I think you're confusing me with somebody else. I'm not counting bubbles in an airlock. I'm using a CO2-calibrated mass flow sensor. It's quite simple and reliable.
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Old 02-03-2013, 05:23 AM   #23
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Sorry MalFet, I did confuse you with an earlier poster. Given an equal molar ratio of CO2 to ethanol, it should be theoretically possible to determine exactly how much ethanol is produced. I guess the issue is that this requires an accurate way to know how much CO2 has been produced during the entire fermentation. I can see how measuring CO2 release would show when the fermentation is dying off, but how would you accurately measure the total CO2 production during the entire fermentation? How reliable is this?

 
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Old 02-03-2013, 12:01 PM   #24
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Quote:
Originally Posted by craigmw
Sorry MalFet, I did confuse you with an earlier poster. Given an equal molar ratio of CO2 to ethanol, it should be theoretically possible to determine exactly how much ethanol is produced. I guess the issue is that this requires an accurate way to know how much CO2 has been produced during the entire fermentation. I can see how measuring CO2 release would show when the fermentation is dying off, but how would you accurately measure the total CO2 production during the entire fermentation? How reliable is this?
If you're measuring rate of CO2 production throughout, the total quantity produced is simply your integral. Some models of mass flow meters have a totalizer built in, but even if they don't the math is simple enough.

It's quite reliable...I land within a point or two consistently.
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Old 02-04-2013, 08:09 PM   #25
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This guy has an interesting approach;

http://tcontrol.rr.nu/

http://www.ebay.com/sch/henielma/m.h...p2047675.l2562

 
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Old 02-05-2013, 03:20 PM   #26
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Quote:
Originally Posted by MalFet View Post
If you're measuring rate of CO2 production throughout, the total quantity produced is simply your integral. Some models of mass flow meters have a totalizer built in, but even if they don't the math is simple enough.

It's quite reliable...I land within a point or two consistently.
Okay, I'd like to know more about your methods. What meter are you using? I've seen quite a few MAF sensors for auto engines, but haven't come across a CO2 specific version on eBay. I can understand how one goes about determining specific gravity from total CO2 produced, but I don't see how you could figure this out by taking only a single measurement toward the end of the fermentation. Total alcohol produced is one parameter that could be taken at any point rather than continuously because most of it remains in the fermenter, whereas CO2 is released from the fermenter. I do see how measuring CO2 output at one point in time would let you know about the relative level of fermentation, i.e. to signal the end of fermentation when CO2 output is low.

 
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Old 02-05-2013, 04:11 PM   #27
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Okay, I'd like to know more about your methods. What meter are you using? I've seen quite a few MAF sensors for auto engines, but haven't come across a CO2 specific version on eBay. I can understand how one goes about determining specific gravity from total CO2 produced, but I don't see how you could figure this out by taking only a single measurement toward the end of the fermentation. Total alcohol produced is one parameter that could be taken at any point rather than continuously because most of it remains in the fermenter, whereas CO2 is released from the fermenter. I do see how measuring CO2 output at one point in time would let you know about the relative level of fermentation, i.e. to signal the end of fermentation when CO2 output is low.
Ahh...there's the rub. I'm not taking a single reading. I'm taking readings at fixed intervals throughout the fermentation. It's easy and reliable.

Mine is a Cole Parmer 33116-series mass flow controller (500sccm, CO2). I got it off of ebay for around $40. CO2 mass flow meters are generally available on ebay (I see several right now), though realistically any meter will work if you're willing to recalibrate it.
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Old 02-05-2013, 04:23 PM   #28
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This was on kickstarter a while back. It wouldn't be using the RaspPi that we all want to incorporate into our brewing, but I think this project is great.
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Old 02-06-2013, 05:46 PM   #29
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Quote:
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Ahh...there's the rub. I'm not taking a single reading. I'm taking readings at fixed intervals throughout the fermentation. It's easy and reliable.

Mine is a Cole Parmer 33116-series mass flow controller (500sccm, CO2). I got it off of ebay for around $40. CO2 mass flow meters are generally available on ebay (I see several right now), though realistically any meter will work if you're willing to recalibrate it.
I've checked this out, and most are reasonably pricey. Nice units from Horiba, but are $250+. The Cole Parmer unit you cite originally cost over $850! Good catch on that. Mouser has MEMS based units that have a 10V input 4V output for air for less than $50. I wonder if these could be calibrated for CO2 output? My thinking is that there isn't much air exchange going on in a fermentation, just CO2 release. So long as CO2 flow could be calibrated (though I'm not sure how to go about this), this would be a reasonable way to measure fermenter activity. BTW, your approach is far cleaner than some of the other methods I've seen for measuring CO2 production.

I have to say that I'm still partial to the ethanol measurement approach since any error in flow measurement is additive during the course of the fermentation, whereas EtOH measurement can be taken at any point.

 
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Old 02-06-2013, 06:11 PM   #30
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Quote:
Originally Posted by craigmw View Post
I've checked this out, and most are reasonably pricey. Nice units from Horiba, but are $250+. The Cole Parmer unit you cite originally cost over $850! Good catch on that. Mouser has MEMS based units that have a 10V input 4V output for air for less than $50. I wonder if these could be calibrated for CO2 output? My thinking is that there isn't much air exchange going on in a fermentation, just CO2 release. So long as CO2 flow could be calibrated (though I'm not sure how to go about this), this would be a reasonable way to measure fermenter activity. BTW, your approach is far cleaner than some of the other methods I've seen for measuring CO2 production.
Those are new prices, though. Second hand units are readily available on ebay for sub-$60. The various gas-specifications are just a matter of a coefficient. There's a simple multiplier to convert between units.

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I have to say that I'm still partial to the ethanol measurement approach since any error in flow measurement is additive during the course of the fermentation, whereas EtOH measurement can be taken at any point.
Sure, it sounds like a great approach in theory. Have you found a sensor that operates in a range useful for homebrewers? I'd like to give it a whirl to see if it actually works experimentally, but the sensor you linked to won't work.
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