Need help monitoring specific gravity or alcohol content

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philba
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Post by philba »

you could try out the bubble thing pretty easily. My guess is that even vigorous bubbling would produce a series of pulses. If it does produce a steady stream of gas (i.e. no bubbles), then you could time how long the "pulse" was and make a volumetric calculation.

I took a google-ride and found this formula for fermentation:
C6H12O6 -> 2C2H5OH + 2CO2

so one molecule of sugar yields 2 molecules of alcohol and 2 of CO2. Thus CO2 is produced at exactly the same rate as alcohol and every 2 molecules of CO2 produced mean one of sugar reduced. compute the mass of the CO2 produced and multiply it times 1/2 the ratio of the molecular weight of sugar to the molecular weight of CO2 and you have the mass of the sugar that was reduced to alcohol and CO2.
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jwax
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Post by jwax »

Try an airlock, and listen. It makes a distinctive click when a bubble- all the same size BTW, pass through. A mike, some acoustic shielding, and in a quiet place to count pulses makes your fermentation detector.
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philba
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Post by philba »

It may work well but I'd be worried about falsing due to noises (the acoustic variety). the noise a bubble makes is pretty quiet so the op amp would need a fair amount of gain.
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GoingFastTurningLeft
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Post by GoingFastTurningLeft »

I stand by the old tried and true method of checking on the bubbles in the wort and letting it sit there about 3 weeks, then I keg it. I have bad luck with hydrometers, they're too fragile. I've broken 2 of them. If you know what you're doing, there shouldn't be any problems. I've never had a stuck fermentation.

This did remind me, i wanted to do a bubble timer thing that let me know the period inbetween bubbles.

One day i'd like to do build some sort of automated thing that will keep the wort temperature constant for mashing, then sound buzzers when it was time to do something. Just set it and forget it!

I think I'm going to try and figure out the pushbutton beer tap first. Now where to find a beer rated solenoid valve... Figure this out, and I'm a step closer to a beer dispensing skee-ball machine. Who wants tickets anyway?
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GoingFastTurningLeft
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Post by GoingFastTurningLeft »

jwax wrote:Try an airlock, and listen. It makes a distinctive click when a bubble- all the same size BTW, pass through. A mike, some acoustic shielding, and in a quiet place to count pulses makes your fermentation detector.
My idea was more along these lines with the cheapo $1 3-piece airlock. The inside part fills up with gas, rises in the vodka (water is a bad idea IMO) gets pinned against the lid, gas bubbles out, it falls back down.

Pop a hole in the lid, put very low actuation force microswitch, or possibly put aluminum foil on top of the inside part with contacts on the inside of the lid. Then have the timer circuit get triggered on the rising edge.
wanderer
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Post by wanderer »

what you need is what is called a displacer. it is a float which does not float on top of the liquid being measured but actually is suspended in the fluid. the upward force exerted on the float is not dependant upon the level but by the specific gravity of the liquid that it is suspended in. I am including a better description from Omega Engineering for everyone here to read.

What I would recomend is a strain gage attached to the suspended displacer inside of a stilling well. also you might want to keep track of the temperature of the wort.

go to the end of the article and read about displacers.

http://www.omega.com/literature/transac ... PRESS.html

Pressure/Density Level Instrumentation
One of the primary principles underlying industrial level measurement is that different materials and different phases of the same material have different densities. This basic law of nature can be utilized to measure level via differential pressure (that at the bottom of the tank relative to that in the vapor space or to atmospheric pressure) or via a float or displacer that depends on the density differences between phases.

Level measurement based on pressure measurement is also referred to as hydrostatic tank gaging (HTG). It works on the principle that the difference between the two pressures (d/p)


Figure 7-1: Click on figure to enlarge.

is equal to the height of the liquid (h, in inches) multiplied by the specific gravity (SG) of the fluid (see Figure 7-1):





By definition, specific gravity is the liquid's density divided by the density of pure water at 68° F at atmospheric pressure. A pressure gage or d/p cell can provide an indication of level (accurate to better than 1%) over wide ranges, as long as the density of the liquid is constant. When a d/p cell is used, it will cancel out the effects of barometric pressure variations because both the liquid in the tank and the low pressure side of the d/p cell are exposed to the pressure of the atmosphere (Figure 7-1B). Therefore, the d/p cell reading will represent the tank level.


Dry & Wet Leg Designs

When measuring the level in pressurized tanks, the same d/p cell designs (motion balance, force balance, or electronic) are used as on open tanks. It is assumed that the weight of the vapor column above the liquid is negligible. On the other hand, the pressure in the vapor space cannot be neglected, but must be relayed to the low pressure side of the d/p cell. Such a connection to the vapor space is called a dry leg, used when process vapors are non-corrosive, non-plugging, and when their condensation rates, at normal operating temperatures, are very low (Figure 7-1C). A dry leg enables the d/p cell to compensate for the pressure pushing down on the liquid's surface, in the same way as the effect of barometric pressure is canceled out in open tanks.

It is important to keep this reference leg dry because accumulation of condensate or other liquids would cause error in the level measurement. When the process vapors condense at normal ambient temperatures or are corrosive, this reference leg can be filled to form a wet leg. If the process condensate is corrosive, unstable, or undesirable to use to fill the wet leg, this reference leg can be filled with an inert liquid.

In this case, two factors must be considered. First, the specific gravity of the inert fluid (SGwl) and the height (hwl) of the reference column must be accurately determined, and the d/p cell must be depressed by the equivalent of the hydrostatic head of that column [(SGwl)(hwl)]. Second, it is desirable to provide a sight flow indicator at the top of the wet leg so that the height of that reference leg can be visually checked.


Figure 7-2: Click on figure to enlarge.

Any changes in leg fill level (due to leakage or vaporization) introduce error into the level measurement. If the specific gravity of the filling fluid for the wet leg is greater than that of the process fluid, the high pressure side should be connected to the reference leg and the low to the tank.

If the condensate can be used to fill the reference leg, a condensate pot can be mounted and piped both to the high level connection of the tank and to the top of the vapor space. The condensate pot must be mounted slightly higher than the high level connection (tap) so that it will maintain a constant condensate level. Excess liquid will drain back into the tank. It is also desirable either to install a level gage on the condensate pot or to use a sight flow indicator in place of the pot, so that the level in the pot can conveniently be inspected.

Either method (wet or dry) assures a constant reference leg for the d/p cell, guaranteeing that the only variable will be the level in the tank. The required piping and valving must always be provided on both the tank and the reference leg side of the d/p cell, so that draining and flushing operations can easily be performed. When a wet reference leg is used, a low thermal expansion filling fluid should be selected. Otherwise, the designer must correct for the density variations in the reference leg caused by ambient temperature variations.

If smart transmitters are used and if the filling fluid data is known, wet-leg temperature compensation can be provided locally. Alternatively, the host or supervisory control system can perform the compensation calculations.

If it is desired to keep the process vapors in the tank, a pressure repeater can be used. These devices repeat the vapor pressure (or vacuum) and send out an air signal identical to that of the vapor space. The measurement side of the repeater is connected to the vapor space and its output signal to the low pressure side of the d/p cell. If the tank connection is subject to material build-up or plugging, extended diaphragm Type 1:1 repeaters can be considered for the service (Figure 7-2).

While repeaters eliminate the errors caused by wet legs, they do introduce their own errors as a function of the pressure repeated. For example, at 40 psig, repeater error is about 2 in. At 400 psig, it is 20 in. In many applications, the former is acceptable but the latter is not.


d/p Cells

Because the designs of the various d/p cells are discussed in detail in another issue of Transactions, only a brief overview is provided here.

The motion balance cell is well suited for remote locations where instrument air or electric power are not available. If a bellows is used as the sensing element in a motion balance d/p cell, an increase in the pressure on either side causes the corresponding bellows to contract (Figure 7-3A). The bellows is connected to a linkage assembly that converts the linear motion of the bellows into a rotary indicator motion, which can be


Figure 7-3: Click on figure to enlarge.

calibrated to indicate the tank level.

In a force-balance type of d/p cell, the sensing element (often a diaphragm) does not move. A force bar is provided to maintain the forces acting on the diaphragm in equilibrium (Figure 7-3B). In pneumatic d/p cells, this is often achieved by the use of a nozzle and flapper arrangement that guarantees that the pneumatic output signal will always be proportional to the differential pressure across the cell. The output of pneumatic d/p cells is linear and is usually ranged from 3 to 15 psig. The levels represented by such transmitted signals (pneumatic, electronic, fiberoptic or digital) can be displayed on local indicators or remote instruments. Pneumatic transmitters require a compressed air (or nitrogen) supply.

Electronic d/p cells provide ±0.5% of span or better precision typically conveyed via a 4-20 mA signal. The range of these simple and robust cells can be as narrow as a draft range of 0- 1/2 inH2O or as wide as 0-1,000 psid. Some electronic d/p cells can operate at line pressures up to 4,500 psig at 250°F. The drift and inaccuracy of some of these units have been tested for periods of up to 30 months, and the errors did not exceed the ±0.5% of span limit.


Difficult Process Fluids

When the process fluid is a sludge, a viscous polymer or is otherwise hard to handle, the goal is to isolate the dirty process from the d/p cell. A flat diaphragm can be bolted to a block valve on the tank nozzle so that the d/p cell can be removed for cleaning or replacement without taking the tank out of service. If it is acceptable to take the tank out of service when d/p cell removal is needed, an extended diaphragm design can be considered. In this case, the diaphragm extension fills the tank nozzle so that the diaphragm is flush with the inside surface of the tank. This eliminates dead ends or pockets where solids can accumulate and affect the performance of the cell. Flat and extended diaphragm-type d/p cells, pressure repeaters, and chemical seals are available to protect d/p cells under these conditions.

Chemical seals, or diaphragm pressure seals, are available with fill liquids such as water, glycol, alcohol, and various oils. These seals are used when plugging or corrosion can occur on both sides of the cell. A broad range of corrosion-resistant diaphragm and lining materials is available. Teflon® lining is often used to minimize material build-up and coating. Level measurement accuracy does suffer when these seals are used. Capillary tube lengths should be as short as possible and the tubes should be shielded from the sun. In addition, either low thermal expansion filling fluids should be used or ambient temperature compensation should be provided, as discussed in connection with wet legs. If the seals leak, maintenance of these systems is usually done at the supplier's factory due to the complex evacuation and backfilling procedures involved.


Bubbler Tubes

Bubbler tubes provide a simple and inexpensive but less accurate (±1-2%) level measurement system for corrosive or slurry-type applications. Bubblers use compressed air or an inert gas (usually nitrogen) introduced through a dip pipe (Figure 7-4A). Gas flow is regulated at a constant rate (usually at about 500 cc/min). A differential pressure regulator across a rotameter maintains constant flow, while the tank level determines the back-pressure. As the level drops, the


Figure 7-4: Click on figure to enlarge.

back-pressure is proportionally reduced and is read on a pressure gage calibrated in percent level or on a manometer or transmitter. The dip pipe should have a relatively large diameter (about 2 in.) so that the pressure drop is negligible. The bottom end of the dip pipe should be located far enough above the tank bottom so that sediment or sludge will not plug it. Also, its tip should be notched with a slot or "V" to ensure the formation of a uniform and continuous flow of small bubbles. An alternative to locating the dip pipe in the tank is to place it in an external chamber connected to the tank.

In pressurized tanks, two sets of dip pipes are needed to measure the level (Figure 7-4B). The two back-pressures on the two dip pipes can be connected to the two sides of a u-tube manometer, a differential pressure gage or a d/p cell/transmitter. The pneumatic piping or tubing in a bubbler system should be sloped toward the tank so that condensed process vapors will drain back into the tank if purge pressure is lost. The purge gas supply should be clean, dry, and available at a pressure at least 10 psi greater than the expected maximum total pressure required (when the tank is full and the vapor pressure is at its maximum). An alternative to a continuous bubbler is to use a hand pump (similar to a bicycle tire pump) providing purge air only when the level is being read.

Bubblers do consume inert gases, which can later accumulate and blanket processing equipment. They also require maintenance to ensure that the purge supply is always available and that the system is properly adjusted and calibrated. When all factors are considered, d/p cells typically are preferred to bubblers in the majority of applications.


Elevation & Suppression

If the d/p cell is not located at an elevation that corresponds to 0% level in the tank, it must be calibrated to account for the difference in elevation. This calibration adjustment is called zero elevation when the cell is located above the lower tap, and is called zero suppression or zero


Figure 7-5: Click on figure to enlarge.

depression when the cell is located below the lower tap. Most d/p cells are available with elevation and suppression ranges of 600% and 500% of calibrated span, respectively, as long as the calibrated span does not exceed 100% of the upper range limit of the cell.

For example, assume that an electronic d/p cell can be calibrated for spans between 0-10 psid (which is its lower range limit, LRL) and 0-100 psid (which is its upper range limit, URL). The cell is to be used on a 45-ft tall closed water tank, which requires a hydrostatic range of 0-20 psid. The cell is located about 11 feet (5 psid) above the lower tap of the tank; therefore, a zero elevation of 5 psid is needed. The d/p cell can handle this application, because the calibrated span is 20% of the URL and the elevation is 25% of the calibrated span.

On interface level measurement applications with a wet leg reference, the high pressure side of the d/p cell should be connected to the tank if the specific gravity of the wet leg filling fluid is close to that of the light layer. It should be connected to the reference leg if the wet-leg fluid's SG is closer to that of the heavy layer.


Special Applications

When the process fluid is boiling, such as in a steam drum, a wet reference leg is maintained by a condensate pot, which drains back into the steam drum so that the level of the wet leg is kept constant. Changes in ambient temperature (or sun exposure) will change the water density in the reference leg and, therefore, temperature compensation (manual or automatic) is needed.

Figure 7-5 describes a typical power plant steam drum level application. The differential pressure detected by the level d/p cell is:





Note that the SG of the saturated steam layer (0.03) and that of the saturated liquid layer (0.76) vary not only with drum pressure but also with steaming rate. This causes the swelling of bubbles when the steaming rate rises (and SG2 drops), as well as their collapse when the steaming rate drops (and SG2 rises). Therefore, to make an accurate determination of both the level and the mass of the water in the steam drum, the calculation must consider not only the d/p cell output, but also the drum pressure and the prevailing steaming rate.


Tank Farms

Computerized tank farm systems usually accept level signals from several tanks through field networks. These systems perform the level monitoring tasks using a variety of compensation and conversion algorithms. The algorithms provide density corrections, volumetric or mass conversions, and corrections to consider the shapes of horizontal, vertical or spherical tanks. These systems can perform safety functions, such as shutting off feed pumps to prevent overfilling.


Floats & Displacers

It was more than 2,200 years ago that Archimedes first discovered that the apparent weight of a floating object is reduced by the weight of the liquid displaced. Some 2,000 years later, in the late 1700s, the first industrial application of the level float appeared, when James Brindley and Sutton Thomas Wood in England and I. I. Polzunov in Russia introduced the first float-type level regulators in boilers.

Floats are motion balance devices that move up and down with liquid level. Displacers are force balance devices (restrained floats), whose apparent weight varies in accordance with Archimedes' principle: the buoyant force acting on an object equals the weight of the fluid displaced. As the level changes around


Figure 7-6: Click on figure to enlarge.

the stationary (and constant diameter) displacer float, the buoyant force varies in proportion and can be detected as an indication of level. Regular and displacer floats are available as both continuous level transmitters and point-sensing level switches.

In industrial applications, displacer floats are often favored because they do not require motion. Furthermore, force can often be detected more
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jwax
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Post by jwax »

Where'd you get a name like "wanderer"?
:smile:
wanderer
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Post by wanderer »

I made up My name from all of the traveling that I do for the work that I do. Since I Graduated From McNeese State University in Dec '93 I have lived and worked everywhere from New Orleans to Chicago, California, Texas, Mississippi, Missouri, Arizona, North and South Carolina, Kuwait, Indiana, Illinois, and LAS VEGAS etc. I work as a Field Engineer on contract basis. My field of expertiese is control systems and applications. I just finished helping to rebuild a Gas Processing Plant on the Beach in Southwest Louisiana that was destroyed by Hurricane Rita. The eye went over the top of the plant and the plant had 10 ft. of Salt Water and mud with 130 mph of winds for almost 12 hrs on top of it. the damage was catastrophic but we were able to get back into production within 6 months.

I have been looking into ethanol production on a small scale ( Farms small Co-OPs ) for about a year now and I think that this is one of our solutions to becoming more self sufficient energy wise. If we can Get The production of energy less centralized we will become less dependant upon other countries and the big oil companies we can be more self sufficient.

enough rambling If you use a displacer you can measure the change in specific gravity with a displacer if you can keep the displacer submerged. I will try to get some time and maybe get a drawing and maybe a simple circuit put together in the coming weeks.
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GoingFastTurningLeft
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Post by GoingFastTurningLeft »

Now the question is, where are you going to get a displacer that you can keep sanitized and is food grade?

I don't even think the big breweries have an automated gravity meter. I'm sure even they use hydrometers.

Don't forget the rule of KISS.

I stick with my method, in the words of Ron Popiel, "Just set it and forget it!"
Engineer1138
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Post by Engineer1138 »

Beer grade solenoid valve:
Get a short length of soft food-grade tubing (Home Depot poly tube should be fine). Put a short, thin bar at right angles to tubing and hold it clamped there with a spring. Valve is CLOSED.
Connect a ferrous object (or use a soft iron bar) to the bar and connect that to the armature of a solenoid. Activate solenoid: valve is OPEN.

Total cost should be around $5 if you can get surplus parts and the only item in contact with the fluid is the tubing. I got some really powerful solenoids from B.G. Micro for about $2.95 a while back.

You can also do the same thing with a servo motor if you grind the circular control wheel into a cam shape and use it to pinchoff/open the tubing.
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GoingFastTurningLeft
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Post by GoingFastTurningLeft »

Sorry to kinda jack your thread... but its still beer engineering
Engineer1138 wrote:Beer grade solenoid valve:
Get a short length of soft food-grade tubing (Home Depot poly tube should be fine). Put a short, thin bar at right angles to tubing and hold it clamped there with a spring. Valve is CLOSED.
Connect a ferrous object (or use a soft iron bar) to the bar and connect that to the armature of a solenoid. Activate solenoid: valve is OPEN.

Total cost should be around $5 if you can get surplus parts and the only item in contact with the fluid is the tubing. I got some really powerful solenoids from B.G. Micro for about $2.95 a while back.

You can also do the same thing with a servo motor if you grind the circular control wheel into a cam shape and use it to pinchoff/open the tubing.
I'm sort of picturing what your saying. But I don't think this design would work for a draft system where the fluid is constantly under pressure. soft polyvinyl tubing also gets pretty stiff when its in the fridge.

I think maybe if i rigged up a solenoid to a draft faucet and used it to actuate the handle it would work. Cobra heads (the black plastic ones that come on 'party keg taps') are pretty inexpensive
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