Water Pressure Transducer

[djsethall]

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.....

 

[halucin8]

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.

 

[kshuler]

I had wondered the same thing. Would be very nice to just dial in a number and have it fill automatically.

Klaus

 

[kladue]

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.

 

[wuertele]

I use this: http://instrumentation.com/crystalmulticalpressuremodule.aspx
I found it on ebay for $30.

 

[Inodoro_Pereyra]

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.

 

[jmer1234]

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.

 

[djsethall]

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

 

[EarthBound]

Why not use a float switch?

 

[djsethall]

A float switch isn't dgital and not really adjustable. My dough in, infusions etc are all different volumes of water. Float switch would be a PITA

 

[kladue]

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.

 

[arturo7]

float valve + position switch

 

[shushikiary]

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

 

[Inodoro_Pereyra]

Why not use a float switch?

A float switch isn't dgital and not really adjustable. My dough in, infusions etc are all different volumes of water. Float switch would be a PITA

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...

 

[kladue]

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.

 

[weirdboy]

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...

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]

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.

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]

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.

 

[kladue]

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]

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.

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]

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.

 

[Inodoro_Pereyra]

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.

 

[LordUlrich]

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.

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.

 

[kladue]

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]

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.

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.

Where did you find that atmospheric pressure would affect the weight of non compressible liquid?

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 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.

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.

 

[kladue]

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]

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]

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.

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.

 

[djsethall]

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.

Whoa, Whoa, whoa. It s the brewers responibilty to make a brew system as complicated and expensive as his wife will allow.......

 

[Sawdustguy]

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%.