The device consists of two parts.

The transmitter resembles a conventional hydrometer made of sterilazable plastic. It has a weighted bulb to which is attached a shaft. There is an annular float around the shaft, retained by a disk on the shaft end.

The float contains a pair of coils, but is othewise very buoyant, having a density of 0.1 or less.

The other component is a receiver which has a simple LCD display.

The sensor is placed in a container of fermenting wine or beer.

The sensor sinks until its density balances that of the liquid. The ring floats on the surface.

A coil runs up the length of the shaft. As the ring moves up and down, the inductance of the coil is changed. Thus as the density of the liquid changes, the position of the ring and thus the resonance varies in proportion, as the winding of the coil is non-linear.

The position information derived from the coil and the temperature of the liquid are transmitted to the display module twice a minute.

This allows the user to monitor the fermentation non-invasively, reducing the risk of contamination and spoiling.

The de luxe receiver can present a graphical representation of density against time, thus allowing the fermentation end point to be more easily selected.
-- 8th of 7, Oct 13 2012

So, the Borg make homebrew?
-- MaxwellBuchanan, Oct 13 2012


[+] cheers
-- FlyingToaster, Oct 14 2012


// Borg make homebrew? //

No, we have simply identified a previously unexploited market niche.

The inductive float approach to level sensing is under review. Optical methods are promising.
-- 8th of 7, Oct 14 2012


The float might be better with a specific gravity of just under 1 or it would sit on the foam.

Anyway, doesn't the foam stick to everything, even the hydrometer shaft, causing potential errors?
-- Ling, Oct 14 2012


Yes. Got any bright ideas?
-- 8th of 7, Oct 14 2012


Yes...the weight loss during CO2 generation is around 4%, so...a set of scales?
-- Ling, Oct 14 2012


For a lower-tech approach, a series of cats could be fitted with weighted belts, such that each cat sunk at a particular liquid density. The density of the liquid could then be measured by the number of cats still meowing.
-- MaxwellBuchanan, Oct 14 2012


//a series of cats//

Ah, the Archifelis principle.
-- Ling, Oct 14 2012


As the float moves up the shaft could you use induction to create electricity? Then use several hundred of these whilst brewing beer to help offset household electricity costs.
-- AusCan531, Oct 14 2012


Oh, I think I've got an idea that won't be affected by the crud or dead cats:

Normally tank levels can be found by bubbling air into the bottom, and the pressure of the air, which causes the bubbles, represents the level of liquid after suitable calibration. It works well with liquids that kill most other sensors.

For the beer: two tubes which bubble air, an exact vertical distance apart. A manometer sits between the two. The pressure of one against the other is dependant on the density of the beer only. Even if everything gets crudded up, should continue to work.

Tad dah!
-- Ling, Oct 14 2012


Very like a pitot tube, then.

Arbitrarily limiting the vertical separation to 100 mm, the pressure difference will be 9.8 x 1000 x 0.1 = 980 Pa.

That isn't much.

The change in S.G. during fermentation is from about 1035 to 1015, about 2% or about 20 Pa.

Add to that the turbulence and noise from the bubbles and the desing would be … challenging.
-- 8th of 7, Oct 14 2012


I suppose if you used a U-tube manometer, the distance between the levels would be...100mm strangely enough(or around 140mm if Alcohol was used). If the tubes were sloped so that the meniscus travelled horizontally more than it travelled vertically, a 2% variation in S.G. could offer a difference of minimum 3mm between meniscii (sp?), depending on the angle.
-- Ling, Oct 14 2012


Hey, go ahead, build a prototype- we're not stopping you.

We're not saying it can't work, just that there are a few aspects that will need very careful thought …

Rather than sensing the meniscus … if you have two parallel tubes, open at the bottom and closed at the top by pressure sensors, then the differential reading between the sensors will be directly proportional to the distance between the openings and the density of the liquid.

The signal would be small, but no doubt a 741 Op-amp would do a reasonable job …
-- 8th of 7, Oct 14 2012


or use something powered by alcohol.
-- FlyingToaster, Oct 14 2012


Perish the thought ...
-- 8th of 7, Oct 14 2012


Wow...I just put a kettle of water on the stove to heat to make beer, and then refreshed the Halfbakery and here we are...

Well, (+) for concept but yes, the bubbles collecting on the device cause it to float higher over time, hindering accuracy. Perhaps small creatures that thrive in beer can be trained to knock these bubbles off for some reward.
-- normzone, Oct 14 2012


//Perhaps small creatures that thrive in beer can be trained //

Did anyone ever mention how big the Borg are?
-- Ling, Oct 14 2012



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