Ideas for liquid density sensors

[Erroneous]

I have 3 ideas for making an electronic hydrometer, wanted to know if you guys have tried anything along these paths:

1) hydrometer/rangemeter:
Pretty simple idea. Aim a range meter at a hydrometer. Keeping it in a fixed place without touching walls would be the challenge. The concept here is to determine the height of the hydrometer above the height of the liquid.

2) weighted barometric pressure sensor:
Put a barometric pressure sensor in say some kind of small bladder that doesn't leak, weigh it down so that it stays on the bottom, and tell your controller the height of the water column. The higher the pressure, the higher the SG.

3) Float attached to a force meter:
have the force meter at the end of a rigid pole, and attached via fishing line to something like a balloon. The harder the balloon pulls on the force meter, the higher the SG.

For 2 and 3, you'd have to calibrate it with a known value, and they wouldn't work so well if the level of the wort changes heights.

 

[passedpawn]

Something like this would be easiest. All the electronics could be outside the clear fermenter. A hall effect sensor or perhaps something optical could see the the angle of the arm inside the fermenter. I've been meaning to do something like this forever, but my money-making ventures keep getting in the way.

 

[Hokie]

I have 3 ideas for making an electronic hydrometer, wanted to know if you guys have tried anything along these paths:

1) hydrometer/rangemeter:
Pretty simple idea. Aim a range meter at a hydrometer. Keeping it in a fixed place without touching walls would be the challenge. The concept here is to determine the height of the hydrometer above the height of the liquid.

2) weighted barometric pressure sensor:
Put a barometric pressure sensor in say some kind of small bladder that doesn't leak, weigh it down so that it stays on the bottom, and tell your controller the height of the water column. The higher the pressure, the higher the SG.

3) Float attached to a force meter:
have the force meter at the end of a rigid pole, and attached via fishing line to something like a balloon. The harder the balloon pulls on the force meter, the higher the SG.

For 2 and 3, you'd have to calibrate it with a known value, and they wouldn't work so well if the level of the wort changes heights.

Someone is apparently on the case:
http://www.fermonitor.com
...but I'd highly encourage competition. You most certainly have time. It was announced in December of 2008 (more or less) and the domain was registered in March of 2010. Needless to say, his concept is "on the slow boat to China", so you might just beat him to the punch.

/I think I'm like the resident skeptic of that device
//only because I'd love for it to be a reality

 

[passedpawn]

Someone is apparently on the case:
http://www.fermonitor.com
...but I'd highly encourage competition. You most certainly have time. It was announced in December of 2008 (more or less) and the domain was registered in March of 2010. Needless to say, his concept is "on the slow boat to China", so you might just beat him to the punch.

/I think I'm like the resident skeptic of that device
//only because I'd love for it to be a reality

You're not the only skeptic. I wrote it off a long time ago. Complexity is the hobgoblin of reliability, and the very vague descriptions of his contraption smells of serious complexity.

 

[Erroneous]

Yes I've seen fermonitor before, though it has a price tag a little bit higher than what I was looking for (something under $50), in addition to having been dormant. Also, I prefer the idea of brew your own as opposed to purchase it outright (as I believe most homebrewers would be).

Passedpawn, the image isn't displaying for me. I'm no physicist/electrical engineer, but I'm guessing that the hall effect would be used to detect the position of a conductive (metal) object, so like a metal hydrometer? Also, something optical would have to be in the right light spectrum to prevent skunking.

 

[passedpawn]

hall effect sensor measures magnetic field. So, if you have a little plastic arm like in the devices above, with a small magnet embedded in it, you could externally measure the angle of the arm by measuring the magnetic field.

 

[Erroneous]

Hmmm... I'm thinking a servo with a range finder except glass blocks ir...maybe throw a red laser onto the arm of a servo and a photo cell, then make the back behind the arm of the device reflective and do a sweep with the servo, record where the light dims and where it brightens again and there you go!

 

[RukusDM]

hall effect sensor measures magnetic field. So, if you have a little plastic arm like in the devices above, with a small magnet embedded in it, you could externally measure the angle of the arm by measuring the magnetic field.

passedpawn has a good idea. This would work very well. Hall sensors are used allot in industry for position measurement. We use them for position feedback in some of our servo positioning systems. Very reliable.

 

[Catt22]

I've often thought that you could do it sonically. ie, somehow generate a sonic ping and measure the return time dolphin style sonar. Perhaps this could be done externally through the walls of the fermenter so penetration would not be necessary and the device could be moved from one fermenter to another.

 

[Hokie]

To all prospective digital hydrometer creators: Don't forget, you have to account for trub (or any solids floating around in there) as well as CO2 build-up. CO2 accumulation I could imagine being a problem for anything that relies on floating devices. Solids might clog or obscure other types of devices. Just a thought.

 

[Erroneous]

Cat22, I've used a sonic sensor for robotics competitions before. They tend to be a bit more accurate than range finders plus/but they detect anything in a 3d cone shape instead of a straight line.

I think the trub would enter the equation more when you weigh the fermenter. The co2 could affect it I suppose, any advice from people who have stuck the hydrometer in the fermenter and left it as to whether or not this is a problem? I didn't have a problem when I did it on my first batch, but I wasn't checking every day.

 

[GlenF]

May be hard to read the hydrometer after krausen film/ scum gets on it.

 

[W00kie]

So, I have a couple ideas for solving this that go back to basic principles. The specific gravity is the density relative to water in this case. The density is the weight per unit volume with correction factors for atmospheric pressure and temperature. Knowing those, it seems all we need to do is measure the weight, volume, atmospheric pressure, and temperature of wort in the fermenter to get a specific gravity value.

Measuring the atmospheric pressure and temperature of the wort is trivial. The real challenge comes when trying to measure weight and volume. The volume could be solved by having a graduated fermentation vessel and then manually entering the volume into the instrument. So that leaves how to measure the weight of the wort.

The obvious way to weigh the wort would be to use some sort of scale that is zeroed out to compensate for the weight of the fermenter and other non-wort things attached. Getting a scale large enough that can be read by some electronic gadget might be something difficult to find.

Another way would be to build a rack that holds your fermenter and has pressure transducers at the contact points between the rack and the fermenter. This should give a fairly accurate measurement of weight.

All of this sounds like a great weekend project with an arduino and some sensors.

 

[Unhelpful]

I like the idea of using a pressure sensor, but measuring the height of the fluid column above it is going to be a pain. If you use two, separated by a known distance, you can measure the difference in pressure between them to determine the specific gravity. A strain gauge attached to a weight of known mass and volume could also work - suspend it in the fluid from fishing line or other thin plastic thread (which we'll assume to have a negligible impact). The difference between the measured strain of the hanging weight and its known weight would be the weight of the fluid displaced by it.

 

[Erroneous]

I like the idea of using a pressure sensor, but measuring the height of the fluid column above it is going to be a pain. If you use two, separated by a known distance, you can measure the difference in pressure between them to determine the specific gravity. A strain gauge attached to a weight of known mass and volume could also work - suspend it in the fluid from fishing line or other thin plastic thread (which we'll assume to have a negligible impact). The difference between the measured strain of the hanging weight and its known weight would be the weight of the fluid displaced by it.

Only trouble is in making the whole thing sanitary. Plus you'd have to have a very accurate pressure sensor that doesn't drift over time. I think a decent system would be an external weight sensor rigged up to a servo or some other mechanical means to move the bucket off the sensor when not in use.

 

[Unhelpful]

The dual pressure sensor design is apparently well-known for digital fluid densitometers. I think the suspended weight has more potential as a DIY, as long as we can find nice weights with accurate weight and volume in good materials.

 

[joebab]

The BeerBug™ - Digital Hydrometer:

http://www.kickstarter.com/projects/parasitx/the-beerbugtm-digital-hydrometer

 

[Erroneous]

The BeerBug™ - Digital Hydrometer:

http://www.kickstarter.com/projects/parasitx/the-beerbugtm-digital-hydrometer

This new link leads me to believe that the beer bug is a bubble counter. It sounds like you have to tell it what the OG is and it can estimate the FG. Great now I can stop pining over a non-existent product!

 

[SgtB]

This is an old post, but I had the same idea today and wanted to throw my idea in the hat. I have a second hand Mettler Toledo SG meter from work. It uses a small glass U shaped tube that's mounted to a resonator. It basically vibrates the tube at a precise frequency, and has either a magnetic or audio sensor that reads the frequency. When you add any liquid to it the frequency changes proportionally to the density of the liquid. Like a tuning fork, heavier = lower frequency.

It seems like a simple device in theory. Getting the feedback loop to work on the resonance would be the hardest part. From there a frequency = density lookup table would do the rest.