Fermenter Airlock Pressure

[Dazza_devil]

How about running a blow off tube out of your enclosure through an airtight grommet and regulating it independantly? Perhaps you could control the CO2 pressure within the fermenter with this method.
How will you control temperature?
Don't forget to allow for the other 50 million variables.
Would you mind elaborating on how you intend to figure in the CO2 pressure or bubble rate with temperature control? Have you got a scientific equation for this relationship?
Are you planning on moderating wort temperature as a result of CO2 pressure or yeast activity/population?

 

[RdeVjun]

Heffo, I would be surprised if there's a pressure sensor within a hobbyist's price range with performance that will discriminate the change in pressure you'd need to tell you anything even remotely interesting let alone useful or that you can act upon (i.e. use for control, but I can't see how it could be anyway), while condensation and an acidic media perhaps could cause strife and diurnal atmospheric pressure fluctuations of much more than a few cm of water could make it noisy too (I'm not sure exactly), albeit over a longer period. I've never used the Digi-key sensors though, so I will stand corrected if they're useful.
If I just had to have some respiration data though, seriously I'd just use a bubble counter. They're about a hundred quid ex-UK, which is quite a bit more than a Digikey AC-T, but they are measuring gas production directly and at least that data would be easily interpreted, whereas pressure data may take some sifting and cleansing. I wanted to get an NCBE bubble counter when I was starting out with this caper, but I soon realised there was little point in doing so as this type of data was largely meaningless and the dough was better off spent elsewhere. I know it might sound interesting measuring this sort of thing, but there's nothing much that is worthwhile knowing about the fermentation process that, if temperature is regulated, can't be learnt from a hydrometer sample and observation. But then again, serendipity is a fine thing too, so as they say, 'whatever floats your boat'!
Bubblers and air locks are a needless distraction but give an anxious brewer some comfort and peace of mind I guess but also a potential source of infection. LHBSes I'm sure take great delight in selling them to nave customers but they are also a major PITA when arranging multiple fermenters in a fridge (i.e. shelves), so I just recommend cling film.
That's my 2c, FWIW, good luck with it! :icon_cheers:

 

[robheffo]

The idea of the pressure sensor is mainly to act as a bubble counter, I am not trying to control the internal pressure of the fermenter in any way (even though this would be possible for very little extra money)

My theory goes as follows...

During fermentation, CO2 is produced by the yeast acting on the sugars in the wort (basic brewing 101 stuff, everyone knows this)
The CO2 is vented as tiny bubbles rising from the wort into the atmosphere, contained within the fermenter.
The airlock, is used as a barrier to stop external contaminants entering the fermenter, creating a one-way (out only) environmental seal.

An air line will be run from the fermenter to a pressure sensor in order to monitor the atmospheric pressure inside the fermenter
The pressure sensor will read an increasing pressure as the internal pressure rises in the fermenter until enough force is contained inside to force it's way through the fluid contained in the airlock.
A computer will read this rise in pressure.
When enough pressure has built up and the pressure is released through the airlock, the pressure sensor will read a sudden drop in the internal pressure.
The computer will read this sudden drop in pressure and will conclude by the drop that the airlock has released a bubble of CO2 gas.

The computer will then be able to log the time of the event, the duration between events and possibly with some calculation based on the pressure immediately before and after the event, it can produce a loose approximation of the amount of CO2 vented through the airlock.

 

[Dazza_devil]

I am not trying to control the internal pressure of the fermenter in any way (even though this would be possible for very little extra money)

I get that but perhaps it may be a more productive excercise.


And when you produce an approximation of the volume of CO2 vented through the airlock.............

 

[MHB]

Let's just assume that you can accurately measure the amount of CO₂ evolved during the ferment (that's a big if) I have (somewhere) a Bibby primary standard rising film gas flow meter, it's good to 3 Litres/Minute (no it's not a bubble counter but its dam accurate) I wouldn't bother connecting it to a fermenter, because it won't tell me anything useful.

Let's wind it back yeast eats a simple sugar and makes 2 Alcohol and 2 CO₂ molecules, yeast don't fart bubbles, they excrete CO₂ into solution, once the beer is saturated with CO₂, the CO₂ starts to form bubbles, these rise to the surface, burst, increasing the pressure in the head space, until it forces its way out of the fermenter, hopefully through the airlock.
For the amount of CO₂ coming out the airlock to be useful you have to:-
Account for the CO₂ evolved before the beer becomes saturated.
Account for the CO₂ still in solution for both of these there is a relationship between temperature and pressure (the amount of agitation caused by the bubbles will also have an effect) that will determine the amount in solution.
Account for the amount of CO₂ still in the beer at the end of fermentation.
Hope like hell that your fermenter is hermetically sealed, that NO CO₂ is escaping anywhere other than where you're measuring it.

Do all that and do it accurately enough for the results to be of any meaning and you have achieved an outcome that a cheap Hydrometer will give you any time you want.

Or if you really want to get technical why not just sit the whole fermenter on a set of scales and data-log the mass loss, it's going to be easier, cheaper and crap load more accurate and reliable.
Or buy a digital hydrometer, gravity to 4 decimal places with ATC to 40^C. (search eBay for "Density Meter" I think there's a second hand one listed).
Otherwise lots of luck your gona need it.

MHB

 

[Dazza_devil]

After observing my fermenter at 10:10pm I noticed a bubble through the airlock. Then there was another one a bit later.
Conclusion; There was enough CO2 in the fermenter to escape through the airlock fluid.

Didn't cost me a cent.

 

[robheffo]

I am starting to think everyone is missing the point or is reading too much into what I am trying to do, quite possibly because I haven't explained the project properly at all.

It is going to be an insulated, 2-zone climate controlled enclosure for 2 fermenters.
It will regulate the temperature to keep the wort in the ideal range for the yeast to do it's thing.
It will log the enclosure and wort temperatures automatically.
It will log the rate at which the airlock bubbles as an indication of yeast activity.
It will log the pressure inside the fermenter.

It WILL NOT be controlling, attempting to control or regulating the CO2 production or pressure in any way.

The pressure sensor will be doing the same job as the currently commercially available bubble counter using pressure instead of Infra-Red light. When there is a small but sudden drop in pressure, a bubble event will have occurred.

If I wanted to accurately record CO2 production I could source an accurate gas flow meter, but if I wanted such a function, I could use the existing pressure sensor to loosely calculate an approximate value without spending any extra money.

The digital hydrometer sounds like an interesting source of information on fermentation progress, If I can source a sensor unit, I would consider adding it to the project.

 

[seravitae]

airlock + blue food coloring + laser/led+bezel + photodiode across top of airlock.

 

[Dazza_devil]

Further Conclusions after observing the airlock,
I don't think the airlock gives a good indication of yeast activity.
There are too many other variables controlling it's bubble rate.