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Old 12-12-2012, 02:50 PM   #1
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Default Digital hydrometer?

Read about beer bug...not for sale yet. Anyone know of a digital hydrometer?

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Old 12-12-2012, 03:02 PM   #2
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I can't wait for the collective brewing geek community to jump on figuring out how it works.

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Old 12-12-2012, 03:15 PM   #3
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Quote:
Originally Posted by hog2up View Post
Read about beer bug...not for sale yet. Anyone know of a digital hydrometer?
Yes, and they are widely used in the brewing, distilling, soft drink and other industries i.e. anywhere that a quick means of determining the composition of a binary or near binary mixture is needed. Do a search on Anton Paar. They seem to be the major manufacturers of these instruments.

They work by measuring the natural (resonance) frequency of a glass U shaped tube into which the substance to be measured is injected. The resonance frequency depends on the mass of the tube which, of course, includes the mass of the material it holds. Given that the tube holds a fixed volume its mass and thus resonant frequency depends on the density of the fluid in the tube. Resonance is determined by exciting the tube by means of an electromagnet near a permanent magnet fixed to the tube itself and then removing the excitation so that the tube oscillates at its natural frequency. The density is prortional to the square of the period (reciprocal of the frequency) of oscillation normalized by a reference frequency. Calibrataion constants are determined by measuring dried air (barometer reading required) and de ionized water. Temperature is critical. To read to 0.000005 (as the best instruments do) temperature must be controlled to a couple of millidegrees) C.

I should note that I'm guessing as to exactly how the natural frequency is determined. Sweeping the excitation frequency while looking for a dramatic phase change between the excitation frequency and the motion (sensed by a second magnet/electromagnet) should work and in the older ones you could hear the frequency varying but in the newer ones you cant. And the salesmen are kind of vague on the details. I put what I did above because the better instruments correct for viscosity which they could do by measuring the decrease in amplitude over time after removing excitation.
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Old 12-12-2012, 03:43 PM   #4
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A.J, the beer bug doesn't seem to have this U-tube and I also wonder how one can determine gravity through resonance while there are CO2 bubbles in the solution. The latter is the case during active fermentation.

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Old 12-12-2012, 04:14 PM   #5
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FWIW, we had a few discussions on realtime gravity measurements in the past. Here is one that has a lot of information and may be connected to the BeerBug: http://www.homebrewtalk.com/f11/real...monitor-85661/

Here is some more info: http://www.kickstarter.com/projects/...tal-hydrometer

There is a sensor that is submerged into the beer.

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Old 12-12-2012, 07:56 PM   #6
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A.J, the beer bug doesn't seem to have this U-tube and I also wonder how one can determine gravity through resonance while there are CO2 bubbles in the solution. The latter is the case during active fermentation.
Ah. I didn't realized that the 'beer bug' was an existing product (or quasi existing product) and so responded to the 'ever heard of a digital hydrometer' question.

Yes, CO2 bubbles are a PITA when measuring fermenting wort or finished beer. Even degassing the beer by the usual means isn't sufficient. What I do is draw the beer into a horse syringe, pull back the plunger to put a partial vacuum on it and then shake like mad. Repeating this a few times seems to do the job. What Anton Paar recommends uses the horse syringe too but they suggest putting pressure on the plunger to compress the bubbles in the U-tube. That works too. This is not workable for a 'in line' process however.

For something that goes into a carboy and is intended to read out continuously my first thought would be to measure the differential pressure between the ambient and a point say 10" immersed in the wort. The differential pressure will be 10*SG WC for 10" immersion. Suitable sensors are available from Ashcroft and others. There will be plenty of engineering challenges such as finding a sensor at a cost less than the example Ashcroft unit I looked up ($179), coming up with a configuration for the sense diaphragm, orienting the diaphragm (presumably upwards so that any bubbles that do form on it get shed), compensating for temperature etc.

I note that the Ashcroft sensor has an accuracy of ±0.4% of span. For a 10" immersion and 10" WC sensor that would correspond to an error of ±0.004SG. I also note that the bug people seem to be pretty carefully avoiding any mention of accuracy (or at least I wasn't able to find anything on it based on a cursory look at the linked site).
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Old 12-13-2012, 03:53 PM   #7
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Further thinking on this has gotten me all excited about what I should be able to do with my cylindroconical fermentors. By attaching a differential pressure gauge one port to the cone and another to the zwickle I would see a pressure difference of

g*(density_wort - density_air)*distance_from_zwickle_to_cone_port

This assumes that there is air, and not wort, in either of the tubes connecting the ports to the pressure gauge. So that leads to a question:
does anyone know where I can get low pressure isolators? These would be made up of a piston or diaphragm with the liquid on one side and air on the other. I know they make them for, for example, isolating fuel in injected engines from the fuel pressure gauge but can't find anything that works at a psi or two.

Note that the scheme I am proposing is not effected by bubbles nor is it affected by barometric pressure or the CO2 blanket, even if the tank has been spunded (i.e. is under positive CO2 pressure).

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Old 12-13-2012, 04:29 PM   #8
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Why couldn't you just fill both tubes connecting to the pressure gauge with wort? Hard to clean and/or find a pressure gauge that would be wort compatible?

I'm not that familiar with conical fermentor terms. Where's the zwickle port? Is that below the top of the wort or up in the headspace?

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Old 12-13-2012, 05:08 PM   #9
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So you mean the drawing below.

But I think the escaping bubbles still affect the pressure difference by reducing the density of the wort. What seems to matter is the weight of the wort column between both ports and that will be less when there are bubbles present.

However, I care most about precise gravity towards the end of fermentation since this is when I want to know how far the beer has to go.

I like the idea. How precise can we get with this and reasonably priced parts?

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Old 12-13-2012, 05:21 PM   #10
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For a bucket or Carboy we could use something like this. For simplicity the ends of the tubes could be left open while pointing down. The only problem with that would be that over time the air in the tubes may get replaced with CO2. I wonder how much that will make a difference, but we could figure that out. The tubes could be thin glass or even better SS.

and if we can fill the tubes with water, at least the distance between the two ports, we could measure the wort to water difference more precisely.

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