Okee Doke. I have been wondering for awhile (ever since I got my PID controller) is there any way to use a pressure transducer in conjunction with a controller or solenoid to be able to just dial in a specified amount of water for a HLT? I hate measuring water in my carboy with a handle and then walking it downstairs (I need to put in a water line in my basement, should be very easy as I put in all new water lines during remodel). Anyways, has anyone ever tried this or am I just getting wayyyy to complicated here? Simple idear here, I want to be able to punch in an amount of water and have it automatically stop the flow of water when it reaches that level. Lets make this pipe dream a reality.....
Water Pressure Transducer
- Thread starter djsethall
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What you need is some sort of programmable flow meter. I use one of these:
Mind you, I got it for free from work. They are around $370 new. Maintenance threw it away.
I pulled it out of the trash, took it apart, put it back together and it worked. It has 1/2"NPT fittings,
so I just put QD's on each end.
Cheers.
Mind you, I got it for free from work. They are around $370 new. Maintenance threw it away.
I pulled it out of the trash, took it apart, put it back together and it worked. It has 1/2"NPT fittings,
so I just put QD's on each end.
Cheers.
I had wondered the same thing. Would be very nice to just dial in a number and have it fill automatically.
Klaus
Klaus
Having built an automated system that does that, it would take a pid controller and pressure transmitter as minimum level control hardware. The Brewtroller would be the next step up as I believe that the BCS hardware is not currently setup for level control.
I use this: http://instrumentation.com/crystalmulticalpressuremodule.aspx
I found it on ebay for $30.
I found it on ebay for $30.
Inodoro_Pereyra
Well-Known Member
You can do that with either a pressure transducer (for liquids, obviously) or a load cell (the heart of a digital scale).
Now, both systems have pros and cons, as usual.
The pressure transducer doesn't really measure the amount of water, but the HEIGHT of the water column above it, as pressure is dependent on height, not volume. That means you'd have to program some sort of conversion table, for the controller to be able to do its job accurately. This would mean some extra work, but would give you the most accurate results in the end.
The load cell would be much easier to set up, since it would measure the weight of the water directly, but it would be dependent on atmospheric pressure, so you'd either have to compensate for AP variances (with a barometric cell, normally cheaper than a liquid pressure transducer), or live with the inaccuracy.
I'd use the first system, even when the programming would be more complicated. What I don't know though, is the effect raising the water temperature would have in the life expectancy of the pressure transducer. If you can find one that isn't affected by it, you shouldn't have a problem.
Let us know how it goes.
Now, both systems have pros and cons, as usual.
The pressure transducer doesn't really measure the amount of water, but the HEIGHT of the water column above it, as pressure is dependent on height, not volume. That means you'd have to program some sort of conversion table, for the controller to be able to do its job accurately. This would mean some extra work, but would give you the most accurate results in the end.
The load cell would be much easier to set up, since it would measure the weight of the water directly, but it would be dependent on atmospheric pressure, so you'd either have to compensate for AP variances (with a barometric cell, normally cheaper than a liquid pressure transducer), or live with the inaccuracy.
I'd use the first system, even when the programming would be more complicated. What I don't know though, is the effect raising the water temperature would have in the life expectancy of the pressure transducer. If you can find one that isn't affected by it, you shouldn't have a problem.
Let us know how it goes.
jmer1234
Active Member
The BrewTroller forum has some discussions around using pressure transducers. What they are doing is effectively creating a sealed sight glass and measuring the air pressure at the top of the sight glass. The last time I looked at it, they were running into accuracy issues during the boil, with temperature changes and liquid turbulence, and were running a bubbler through the sight glass to keep a slight positive pressure on the tube, thereby keeping it clear, and averaging the pressure measurements.
Sorry I do not have a link, just putting this out as I am running out the door to work.
Sorry I do not have a link, just putting this out as I am running out the door to work.
OP
OP
djsethall
Well-Known Member
This would be for the HLT only, no boiling, no acidic envrionment, just water. Oh yeah, in order to match, the parts should be stainless.
http://www.sensorsone.co.uk/products/252/39/LMK331-Screw-In-Ceramic-Level-Transmitter.html
sorta like this, screwed into the side of my hlt, then ran to a pid controller with zero overshoot. I would probably need to have a table with all the values for 1/4 gallon increments, but, it would be cooler than what I got now
http://www.sensorsone.co.uk/products/252/39/LMK331-Screw-In-Ceramic-Level-Transmitter.html
sorta like this, screwed into the side of my hlt, then ran to a pid controller with zero overshoot. I would probably need to have a table with all the values for 1/4 gallon increments, but, it would be cooler than what I got now
EarthBound
Well-Known Member
Why not use a float switch?
Here is a lower cost liquid pressure transmitter http://www.meas-spec.com/product/t_product.aspx?id=5061 nominal street price is around $120. This is a plastic body unit so it would be best to mount it below the keggle and use at least 3 inches of tubing to isolate it from the heat. The 0-5 volt output will work with all the voltage input controllers or the Brewtroller platform without using another amplifier circuit. The cheapest wet sensor out there is the Honeywell series 26 wet sensors, but they would need an amplifier to change the millivolt reading to 0-5 volt range to be really usefull.
Direct mounting a pressure sensor on the pot or keg will cause shifting readings as the sensor calibration changes with the temperature despite the claims to the contrary by the manufacturer.
Direct mounting a pressure sensor on the pot or keg will cause shifting readings as the sensor calibration changes with the temperature despite the claims to the contrary by the manufacturer.
arturo7
Well-Known Member
float valve + position switch
shushikiary
Well-Known Member
I'll put this here:
http://www.brewtroller.com/forum/showthread.php?t=538&highlight=liquid+sensor
and suggest this sensor:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MPX5010DP-ND
http://www.brewtroller.com/forum/showthread.php?t=538&highlight=liquid+sensor
and suggest this sensor:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MPX5010DP-ND
Inodoro_Pereyra
Well-Known Member
You could use a potentiometer type float sensor, kinda like the ones in cars' gas tanks. They'd probably be a lot more rugged than the pressure transducer, and they sure are cheaper...
The FreeScale sensor price looks good, +- 5% accuracy could be a problem if there is no way to scale or apply an offset value to the signal to correct for calibration error. Automotive sending units are quite a bit more expensive and the materials they are made of would not be what you want in contact with the water or wort.
This is what I was thinking. Not an on/off float switch but a potentiometer or similar where the output signal changes with the height of the float.
Inodoro_Pereyra
Well-Known Member
You don't need an automotive sending unit. A standard potentiometer with a food grade float (an empty soda bottle, for example) would do the job nicely.
Sawdustguy
Well-Known Member
The problem with the float and potentiometer is that the system is very prone to water surface disturbances. Any slight disruption in the water's surface will cause the reading to fluctuate because the float will move. A slight movement of the float can cause large errors. Measuring the pressure of air in a tube compressed caused by the weight of the water is the ideal if cold water is used and high temperature does not come into play. It is a simple setup.
For those folks that want a simple switch setup, look at the adjustable water level switches for washing machines. You will have to create a dial face marked in gallons, but it will respond to changing levels and shut off a fill valve on rising level. For the next step up, analog output, floats are not such a good idea as they would require the pivot to be mounted at the 50% point and some type of linkage to place the electronics above the waterline. There is a reason this method is not found in real world situations outside of closed tanks in automotive applications where the parts are not exposed or likely to get in the way.
Inodoro_Pereyra
Well-Known Member
Not at all. A pivoting arm would be a bad idea, because it'd introduce a linearity error in the reading. Using a potentiometer/float setup is as easy as weighing down the float enough to move the potentiometer down through a wheel and a piece of cord, and setting up either a spring or a counterweight for the potentiometer to move in the opposite direction, when the float is pushed up. That way, there's no need to put anything inside the tank, except the float.
I don't know in the US, but in other countries (like mine) that's a very popular setup to measure the level in water tanks and the like.
Finally, there's also a reason why potentiometer setups are used in cars' gas tanks: unlike most other methods, they're insanely rugged, unlike pressure transducers, they don't lose their calibration, and they're very cheap to produce.
LordUlrich
Well-Known Member
In my fluid mechanics lab we used a set of two metal rods at a fixed separation to measure water level (it is hyper accurate, we were measuring wave heights in a flume). You essentially measure the resistance between the rods which varies with the depth of water.
Perhaps the simplest (depending on your setup) is to weight the water with a scale of some sort, water weights 8.3 lbs/gallon (at room temp), and unlike depth is independent of any surface disruption. Just make sure to zero your reading before you start to fill.
Perhaps the simplest (depending on your setup) is to weight the water with a scale of some sort, water weights 8.3 lbs/gallon (at room temp), and unlike depth is independent of any surface disruption. Just make sure to zero your reading before you start to fill.
Inodoro_Pereyra
Well-Known Member
The 2 rod method is actually a great way to measure the water level, as long as the quality of your water is consistent (like, for example, if you use a good quality filtering system). You can even place the rods farther away at the bottom, and closer at the top. to get more sensitivity.
The use of a scale is only accurate if you use a balance.
If you use, for example, a digital scale, the atmospheric pressure will introduce an error at the time of measurement, unless the AP at that time is exactly the exact same AP at the time the scale was calibrated.
The use of a scale is only accurate if you use a balance.
If you use, for example, a digital scale, the atmospheric pressure will introduce an error at the time of measurement, unless the AP at that time is exactly the exact same AP at the time the scale was calibrated.
LordUlrich
Well-Known Member
Yes, but lets thing about how much error for a minute, an pretty big change in atmospheric pressure is about 1 millibar per hour, which relates to .4 inches of water (about a qt in my kettle). So yes you need to zero when our system when you start, if you go by weight you really need to measure CHANGE in weight, not the actual reading from a load cell.
Also a balance will introduce an error if the area of the counterweights is not the same (or actually the moment of area i think) as the thing you are weighing. IF you put a pot on the plate of a balance that is smaller than the bottom of the pot you will see an error.
Where did you find that atmospheric pressure would affect the weight of non compressible liquid?, in all the load cell equipped tank measuring systems that I have purchased and installed I have never seen mention of or provisions for atmospheric pressure readings. The cost and complexity of load cell systems is such that they have very limited use in industry, pressure, ultrasonic and radar distance measuring devices are the normal methods of determining tank volume. I am curious where you found a potentiometer level system used for tank levels that still is in service, and who made it, I thought those devices went away when the cheaper pressure transmitters came into service because of accuracy problems with the gears and potentiometers.
Inodoro_Pereyra
Well-Known Member
True, but the error introduced by the balance is negligible, compared to the error introduced by a normal scale. In the scale, it doesn't matter if you zero it before measuring. The same mass will produce a bigger force (weight) on the load cell, for a higher barometric pressure. True, the error may not be significant for some of us, but the op is looking for an accurate system, and there are more accurate (and more affordable) systems out there.
It has nothing to do with substance compression. Weight is a force, and changes with barometric changes, and altitude. Load cells measure the weight needed to deform them, as a load cell is basically a spring.
A balance does not measure weight. It compares mass. Mass doesn't change.
I'm Argentinian. In Argentina, potentiometer type systems are the systems of choice for water tanks, especially those in tall buildings, for their extreme ruggedness. Sure, more advanced methods are more accurate, but, as far as I know, nothing beats the reliability of a potentiometer system.
I still have difficulty trying to understand the physics involved with barometric pressure affecting load cell weight measurements when an open top tank is surrounded with air at same atmospheric pressure. The force of the air should be equal from all directions and the effects should cancel each other regardless of air density or temperature.
Special Hops
Well-Known Member
You guys are getting way to complicated. Volume is what you ate going for. Mark your HLT at the level you need. Then just shut of the water when you teach it. Keep it simple.
Inodoro_Pereyra
Well-Known Member
I don't have the formal training to give you a scientific answer for that. All I can tell you is that that's the main difference between a spring scale (like the digital scale we're talking about) and a balance. It's not that the spring scale is exclusively affected by barometric pressure. It's said it's affected by gravity, meaning the combination of the Earth's pull on the object being weighed, and the weight of the air column over it.
But that's about the extent of my knowledge on it. Maybe one of the forum's engineers can give you a better answer.
Either way, so far, I think the idea of measuring the impedance between 2 rods is by far the best one, for this application. It's accurate, affordable, and as reliable (in the long run) as you want to make it.
OP
OP
djsethall
Well-Known Member
Whoa, Whoa, whoa. It s the brewers responibilty to make a brew system as complicated and expensive as his wife will allow.......
Sawdustguy
Well-Known Member
Gravity does indeed change with altitude but the difference is very, very small. The gravitational force above the Earth's surface is proportional to 1/R2, where R is your distance from the center of the Earth. The radius of the Earth at the equator is 6,378 kilometers, so let's say you were on a mountain at the equator that was 5 kilometers high (around 16,400 feet). You would then be 6,383 kilometers from the Earth's center, and the gravitational force would have decreased by a factor of (6,378 / 6,383)2 = 0.9984. So the difference is less than 0.2%.
cruelkix
Well-Known Member
Exactly right. I remember when I learned this in school. I was so pissed off cuz I realized that NASA and teachers had been lying to me through my whole childhood. Astronaunts in space are not in "0 gravity". They are orbiting the earth (just like all our satelites) in a perpetual free fall. The gravity feild they are is lower, but not even close to 0. It made me mad lol.
Back to the OP. From all the searching I have done, pressure is the cheaper way to go. I would prefer a load cell personally. No temperature to mess with and pretty darn accurate. Price is the issue, as well as mounting the HLT properly. I can't seem to find cheap load cells.(rip them out of a bathroom scale?)
Inodoro_Pereyra
Well-Known Member
Well, sorry, but you're gonna be mad again. Astronauts in space can be in "0 gravity" in either of 2 cases: if they are orbiting the Earth at a speed and distance high enough that the centrigugal force and the Earth's gravity cancel each other, or if they're in a specific part in space (so far, only between Earth and Moon) in which both gravities do the same.
A "perpetual free fall" is an oxymoron, since "falling" means getting closer to something. You are in a free fall when you're inside NASA's Reduced Gravity Airplane, because, even when you experience weightlessness, you are falling towards Earth. The only difference is that, since your "atmosphere" is falling with you, you don't feel the fall.
cruelkix
Well-Known Member
This is completely off topic, but you are arguing the same semantics that NASA is. You are not in 0 gravity. You are using some other method to "cancel out" the effects of the earths gravitational pull. And you can argue the same about your "falling" comment. It's all a matter of how you interpret things. It's like a bathroom scale. There is a lot more going on than just your weight, but that's all its showing you because that's all you want to see. Different ways of looking at things. I like to see all the numbers, not just the absolutes.
Inodoro_Pereyra
Well-Known Member
No, I'm not arguing semantics. "0" is a number, a mathematical expression. "0" is the product of 2 or more mathematical expressions "cancelling each other". "0 gravity" is the product of 2 or more forces (one or more being "gravity" cancelling each other. Otherwise, since "gravity" is a function of mass, "0 gravity" would only exist in a universe that's completely devoid of mass, a perfect vacuum. And since matter can't exist in a perfect vacuum, obviously, no human being could ever experience 0 gravity, first, because tat human being could not exist in a perfect vacuum, and second, because, no matter how far away the nearest speck of dust is, it'd be exerting gravity over him/her.
As per "falling", there's nothing to argue about it. By definition, "falling" means "descending". To "descend", you need to have an attractive force, pulling you down, and, for that, you need matter exerting that force, which will eventually "stop" that fall. So "perpetual free fall" is really "perpetual nonsense".
cruelkix
Well-Known Member
"0 gravity" is the product of 2 or more forces (one or more being "gravity" cancelling each other. Otherwise, since "gravity" is a function of mass, "0 gravity" would only exist in a universe that's completely devoid of mass, a perfect vacuum. And since matter can't exist in a perfect vacuum, obviously, no human being could ever experience 0 gravity, first, because tat human being could not exist in a perfect vacuum, and second, because, no matter how far away the nearest speck of dust is, it'd be exerting gravity over him/her.
As per "falling", there's nothing to argue about it. By definition, "falling" means "descending". To "descend", you need to have an attractive force, pulling you down, and, for that, you need matter exerting that force, which will eventually "stop" that fall. So "perpetual free fall" is really "perpetual nonsense".
You are arguing semantics as well as being argumentative
. As I said before it all depends on how you want to look at it. In this case the 0 is what you want to see. That zero however is not absolute just as you stated. And your "descend" statement is relative to time and the plane you are using as a datum. Again its how you want to look at it. We are both right and both wrong. Now stop it This isn't the place. Let's head over to a physics forum or something 
Inodoro_Pereyra
Well-Known Member
Yeah, whatever. I'm arguing physics and mathematics, not semantics. However, you're free to believe what you want to believe. I prefer facts.
As far as I'm concerned, if you want to believe gravity is part of a conspiracy to keep us all on the ground, the more power to you. The fact remains that neither NASA nor your teachers lied to you.
But you're right: this is not the place. And you're obviously not the person to have a physics discussion with.
As far as I'm concerned, if you want to believe gravity is part of a conspiracy to keep us all on the ground, the more power to you. The fact remains that neither NASA nor your teachers lied to you.
But you're right: this is not the place. And you're obviously not the person to have a physics discussion with.
Atmospheric pressure is a force exerted in ALL directions. It is pushing the scale UP just as much as it is pushing it down just as much as it is pushing it left just as much as it is pushing it right. There should be no change at all based on atmospheric pressure UNLESS the scale were made completely air tight, such that there would be a pressure DIFFERENTIAL between the top and bottom of the plate, in which case the weight reading WOULD be affected. You should be able to pressurize whatever you are weighing on whatever kin of scale to as high as you want and get the same reading. Atmospheric pressure balances out and the force you are reading from the scale is the mass times the gravity.
I have always used weight for brewing and calculated the volumes. Much more accurate this way.
Klaus
ClaudiusB
Well-Known Member
Some info from SCIENTECH BALANCES
There is no certificate of calibration included with any balance we sell since this can only occur at the place of installation. Every location in the world is positioned differently to "magnetic north" and therefore the acceleration of gravity is slightly different. Add to this barometric pressure effects the acceleration of gravity depending upon your location's altitude to sea level.
Cheers,
ClaudiusB
Inodoro_Pereyra
Well-Known Member
Don't bother Claudius, you're wasting your time.
First, they believe that gravity is an illusion, and now they figured the atmosphere weighs upward. Makes no sense to keep arguing.
They can believe whatever they want to believe. Now, they think that buying a pressure sensor, and eventually a buffer for it, is cheaper than cutting 2 pieces of tube, and attaching an ohmmeter to them. Whatever. I'm done with this thread.
First, they believe that gravity is an illusion, and now they figured the atmosphere weighs upward. Makes no sense to keep arguing.
They can believe whatever they want to believe. Now, they think that buying a pressure sensor, and eventually a buffer for it, is cheaper than cutting 2 pieces of tube, and attaching an ohmmeter to them. Whatever. I'm done with this thread.
I will look into the pressure affecting the scale thing--- this most liekly means that the pressure sensor (generally a strain gauge) is a sealed device that will respond to a pressure differential, but I'll look ino it when I get home from work. But Inodor Pereya seems to not understand the concept of pressure. A gas, amazingly, is not a solid. It doesn't act like a solid. Stack some solids on top of each other and, yes, the pressure is all downward. Pressurize a GAS, however, and it presses equally everywhere. Think I don't know what I'm talking about?
Here's a quote from NASA. Now, they probably have SOME idea about pressure being that they employ all sorts of fancy engineers and scientists and things. (http://www.grc.nasa.gov/WWW/K-12/airplane/pressure.html).
https://files.me.com/kshuler/pfh9fq
"the pressure pushes on the bottom of the box and on the sides. This is different from simple solid mechanics. If the red gas were a solid, there would be no forces applied to the sides of the box; the applied force would be simply transmitted to the bottom. But in a gas, because the molecules are free to move about and collide with one another, a force applied in the vertical direction causes forces in the horizontal direction. "
As I said, pressure is applied in all directions in a gas. It is like a balloon- pressure is exerted equally to all surfaces.
Enjoy.
Klaus
Here's a quote from NASA. Now, they probably have SOME idea about pressure being that they employ all sorts of fancy engineers and scientists and things. (http://www.grc.nasa.gov/WWW/K-12/airplane/pressure.html).
"the pressure pushes on the bottom of the box and on the sides. This is different from simple solid mechanics. If the red gas were a solid, there would be no forces applied to the sides of the box; the applied force would be simply transmitted to the bottom. But in a gas, because the molecules are free to move about and collide with one another, a force applied in the vertical direction causes forces in the horizontal direction. "
As I said, pressure is applied in all directions in a gas. It is like a balloon- pressure is exerted equally to all surfaces.
Enjoy.
Klaus
