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Posted: 2/23/2006 4:08:07 PM EDT
[#1]
Thermocouple and some kind of device to record the temperature of the water.
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Posted: 2/23/2006 4:08:31 PM EDT
[#2]
Use a float. It could be connected to a rod that comes out the top, so you wouldn't have to penentrate the tank.
Hook it up like on a sump pump, with limit switches. They could be used to turn off the burner, or be used to add make-up water. Why not just keep it simple. |
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Posted: 2/23/2006 4:11:14 PM EDT
[#3]
First off. Is it a water purification still? or a other use still
if its a still....not for water use, then you dont want it to boil at all, you want the temp to be 174 deg-F , 78c and not a bit higher. You dont want to go any higher than 180F, unless you want water vapor and other crap in your finished product. This is because ethanal boils off at about 174F. You should install a PID temperature controller as an electronic thermostat that uses a thermister. You will have to penetrate the outer wall to do so though. But if its a water purification still then you can just let the still go unregulated to a full on boil at around 220+ deg-F. |
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Posted: 2/23/2006 4:12:49 PM EDT
[#4]
He should switch to gas. 
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Posted: 2/23/2006 4:19:06 PM EDT
[#5]
btw, the professional industrial water purification stills use and electrode that is installed at the level they want the heating element to shut off at, then a relay will shut off the elements.
moonshiners back in the day would just measure the specific gravity of the wort to figure out how much potential alcohol was in the wort, say 18%. Then they would just run the still until they got the 18% +/- .5% out in spirits the shut down the still. Pretty simple math and chemistry. |
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Posted: 2/23/2006 4:24:26 PM EDT
[#6]
Thermal Imager.
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Posted: 2/23/2006 4:30:50 PM EDT
[#7]
Weld a thermocouple to the bottom of the tank. When the temp spikes up, the water is gone and you can shut off the heat. My rice cooker works like that and so does my coffee pot, stone cold simple and utterly reliable. If you have to know the level, an external sight tube works great. You can put simple optical detectors at various points if you just want to know over full, full, almost empty, and empty. |
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Posted: 2/23/2006 4:34:48 PM EDT
[#8]
+1. I was pulling my hair out until I got to Thuban's post. 
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Posted: 2/23/2006 5:04:36 PM EDT
[#9]
A slightly spendy method would be this:
It involves electronics and a computer. Computer can be a $8 Microcontroller. Thermocouple on tank lower edge. Shape tank uniformly (not big at bottom, small at top). The controller will read the temperature 10 times a second to "plot" a temperature curve. (in memory, a list of numbers). Once 10 readings show the temperature to be higher on the curve, there is less water, and then have it shut off. Total cost: Thermocouple (depnds, $0.50 to $200, probably around $10) Microcontroller - $8, Supporting electronics $15, SSR (Solid State Relay) for switching Heating Element: $30 I will quick draw a plot that the computer would look at:  The curve is very exaggerated, and the cuttoff would only be about 2 degrees up. Plotting this could be done fairly easily with a PC Based Multimeter (works through parallel port), you can get the software for cheap to free. Hook up across the thermocouple and support components, and have teh PC draw you a graph of the temp from cold to near boil to rolling boil, to dry (where the heat will spike). Run that a few times, and you would have the data points for shutoff ready if you wanted to have it "computer controlled", it would then just be a matter of 2 pins from your computer's parallel port out to the electronic board at the tank, and one to the SSR to control the heat. |
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Posted: 2/23/2006 5:07:25 PM EDT
[#10]
you justy described a PID controller. $50 on ebay. |
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Posted: 2/23/2006 5:12:10 PM EDT
[#12]
Get a scale.
Subtract the tare of the unit, dry. When it reads zero, shut that bitch down. Or hook up a switch so when the scale reads 0 it powers down |
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Posted: 2/23/2006 5:22:22 PM EDT
[#13]
Wow! A snazzy package/interface on top of it! What I posted above was just the temp area from a pulse charger I builit for NiMh Batteries with a temperature controller, voltage ramp monitor, current limiter, and a "learning mode" for each battery at the beginning of the cycle. It won't overcharge, but will get the best life out of what is left on a "dead" rechargeable. Not something I want to build again, it got spendy. Fastest charger I own, better than the $200 ones, and has more features.  I would hence recommend one of those for your needs. I didnt' look at the specs, but you want one with a fast response time thermocouple, and a high temperature sample rate (minimum of 1 second samples) |
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Posted: 2/23/2006 5:28:47 PM EDT
[#14]
Omega has a lot of nice off the shelf PID controllers that could be used in a manner like brass described.
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Posted: 2/23/2006 5:30:03 PM EDT
[#15]
Just thought of a second method that would be MUCH Simpler and Very Accurate:
Where the steam escapes, put a water vapor sensor. When the sensor falls below "high steam", cut off the heater. Again, use an SSR, as mechanical relays are slow, they arc at the voltage/current levels we are dealing with on the heating element, and they never wear out. Water Vapor sensor: Simple as two wires mechanically held a short distance apart (1/8" or less, and parallel), and measure the resistance (it will be in the megohms, but there). When the resistance goes to infinity, there isn't any more water vapor, and it would turn off the heating element. Instead of resistance, you could measure the capacitance between the two wires (which would need to be small squares to be measurable). Air has a much higher dielectric constant than water vapor, so when the capacitance goes up, it stops the heating element. Instead of a microcontroller/computer, this could be monitored with a high frequency oscillator using a couple of op-amps (one for frequency generation from the capacitance leads, one as a comparator to trigger the SSR). The resistance method above could also be done with op-amps, keeping the total price under $10 if you have a decent grasp of electronics. |
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Posted: 2/23/2006 5:36:11 PM EDT
[#16]
If it is boiling, and teh tank is enclosed , it wont be TOO long before EVERYone knows, because IT WILL BLOW UP!!! |
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Posted: 2/23/2006 5:39:59 PM EDT
[#17]
 PLEASE tell me what electronics books to buy. Assume nothing. I'm serious. |
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Posted: 2/23/2006 6:15:47 PM EDT
[#18]
Guys,
I know the scale method is simple but I can't use it either. Scott |
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Posted: 2/23/2006 6:26:48 PM EDT
[#19]
I don't think this will work. I need to shut down before the temp rises (ie: the water is still boiling but the water level is low) |
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Posted: 2/23/2006 6:27:17 PM EDT
[#20]
Ok here is how to do it.. Surefire way..
Fill the still with water and turn on the heat.. While the water is heating get yourself the following things.. 1-750mL bottle of Jack 3-fluffy kittens 1-1,000,00 mF capacitor Now with the water heating proceed to pour yourself a big glass of Jack while charging the capacitor.. When the glass is full and the capacitor is charge start to juggle the kittens.. For every kitten you drop pound the glass of Jack and shock yourself with the cap.. When the bottle is empty and you have stopped and restarted you heart many times over.... LOOK INSIDE THE STILL AND CHECK THE WATER LEVEL!!!!! 
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Posted: 2/23/2006 6:58:05 PM EDT
[#21]
Why can't you just watch how much comes out of the thing and use it to estemate how much is left inside.
It seems like you're making this much harder than it needs to be. |
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Posted: 2/23/2006 7:23:50 PM EDT
[#22]
Because this thing is turned on and nobody watches it. It is suppose to be automatic. |
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Posted: 2/23/2006 7:27:52 PM EDT
[#23]
Poke a hole in the bottom of the tank. If no water comes out, it's empty.
It'll work at least once. |
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Posted: 2/23/2006 7:38:17 PM EDT
[#24]
tie a string to an egg and then pull it out a few minutes later.
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Posted: 2/23/2006 7:44:56 PM EDT
[#25]
WEIGH IT
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Posted: 2/23/2006 7:50:15 PM EDT
[#26]
A pressure sensor on the outside (bottom) of the vessel to detect the weight of the vessel. Calibrate it such that when the weight falls below your "safe" level, it turns the heat off.
What do I win?
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Posted: 2/23/2006 8:02:23 PM EDT
[#27]
tap on it and measure the pitch.
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Posted: 2/23/2006 8:07:06 PM EDT
[#28]
You can’t use the weight of the tank.
You can’t use a float. You can’t use temperature. You can’t detect the vapor. You can’t use the conductivity of the liquid or any kind if internal sensor. Did I miss anything you can’t do? We’re sorta running out of options here I guess you could carefully control how much power your device pulls then do some calculations on how long it will take to boil the water off. That would work better if you preheat the tank and insulate it well. Then you could run the device on a timer. (I think a 1000 watt heater will vaporize about a quart and a half of water an hour.) |
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Posted: 2/23/2006 8:18:42 PM EDT
[#29]
WTF IS THIS FOR!?!?!
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Posted: 2/23/2006 8:22:36 PM EDT
[#30]
A small (household size) water purifier/distiller for turd world countries. |
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Posted: 2/23/2006 8:23:56 PM EDT
[#31]
Instead of using a Calrod or similar resistive element, get yourself some platnium electrodes and use the resistance of the water itself to boil it. Old vaporizers used this, except they didn't use platnium for the electrodes. IIRC, they were just nickel. You will need a large surface area to effect enough power.
Once the water level drops, the resistance increases and the heat stops. Since I assume you are using AC, there is no electrolysis. A little off gasing won't hurt the product anyhow. But if you are powering it from your truck, you need something else. Yes, the platnium electrodes are pricey but hey, you wanted it simple and foolproof. You do know you will have a scale problem, right? It won't hurt the electrodes but they will need pickling since the scale will act as an insulator. BTW, distillation is the EXPENSIVE way to deionized water. |
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Posted: 2/23/2006 10:39:19 PM EDT
[#32]
Not sure.. I know Elect Engr in college didn't teach me what I know, mostly was looking at a problem, and finding a solution. Once you know how to wire-wrap well and breadboard, then you can snap together "known good" sub-circuits into something you want. Once at that point, redesign the whole thing to be homogenous, rather than a bunch of specialized parts doing "almost the right thing". I would recommend the 6 volumes of Electronics Circuit Reference, a beginner book from B&N/Amazon, Forest M Mimms is a good author (did some very basic books for Radio Shack). Learn how to use a DMM, get a Good DMM above all else. Quality w/features. Most of Flukes "Electronic Field" meters, starting at the 12B fill this, but the 12B would be the minimum. Once you have a breadboard, a good meter to measure current from microamps to about an amp, and the concept of how feedback and filter circiuts work (the analog electronic version of Integration and Differential EQ). I can sum it up easily: How to make a stable power supply of the right voltage/current/filtering. The filters to pass/block frequencies, used in about everything from feedback to detection. Amplifiers, how transistors are biased to make different amplifiers, and how the passive components work. You can read a ton of math about the phase changes between AC through a capacitor and an Inductor, but when you start making it work, that kind of just goes into the background and things get tweaked around until you learn what does what. Kind of like the WESCOG of the electronics world. 2nd best advice: Find a HAM club local and sign up. Build your own radio, amp, antenna, and other gear. |
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Posted: 2/23/2006 11:46:12 PM EDT
[#33]
Scott, If there is no pressure differential, then you have an open vessel. You can measure the level with a sight glass mounted to the side of the tank. Even with a closed vessel, they make a pressurized sight glass and you can monitor the level. With a sight glass, you can mount a detecter to the glass itself that can be used to trigger an alarm or a fill valve (or both). As you don't want to penitrate the tank, mount the bottom of the glass on the inlet piping and the top to highest point in the exhaust line. You will have to have some inlet/outlet piping and it'll be easy to "T" to the lines. |
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Posted: 2/24/2006 12:53:29 AM EDT
[#34]
You either got to provide pics or explain better, becuase there are only so many ways you can tell when water is at a certain level and then have a cut off switch do it automatically. You dont seem do want to do either a Analog or Digital route! Most of the ways already listed are the only ways to do this. The only one not mentioned yet that i can think of is a thermistor. I order to prevent the heating element from burning out once the water level gets low the heater will get really hot and use up much more electricity. So the Temprature sensative thermistor will increase in Resistance until the heating element shuts off automatically. Once the electricity is shut off have a secondary relay switch (which will detect a 0 voltage or 0 current) turn the whole thing off permantly. As once the temprature drops the themistor will just restart the curcuit. it's complicated electronics but it's as far as my thinking goes. BTW- this is how Aquarium heaters work to prevent an overheat.
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Posted: 2/24/2006 2:37:05 AM EDT
[#35]
Rather than a shut-down, what about a way to add water when the volume in the tank gets too low? Use the "water seeks it's own level" property to ensure that the tank won't run out, as long as the backup tank is full. Use a one-way flow valve so water can enter the tank to keep it full, but can't leave the tank. As long as there is no pressure, this should work.
Or just a sight glass? For example, a large glass tube, alongside the tank so as the water level goes down, water flows out of the tube and into the tank. That's how steam locomotive operators were able to tell how much water was in the boiler. For the operators, it was literally a matter of life and death. If you had any pressure, you could use a low water alarm, which sounds a whistle when the bottom of the pipe gets uncovered with water, and the air pressure is released to escape out the whistle. |
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Posted: 2/24/2006 2:38:11 AM EDT
[#36]
Couldn't this system add water, when the circuit closes, too? |
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Posted: 2/24/2006 4:29:09 AM EDT
[#37]
How about a flapper valve over the outlet for the steam. The steam will increase the pressure in the tank and lift the valve, once there is no water there is no steam and the pressure decreases. The flapper valve is hooked into the heating element power supply and cuts it off when the valve closes. |
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Posted: 2/24/2006 7:34:38 AM EDT
[#38]
That is too subject to fouling. |
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Posted: 2/24/2006 7:55:18 AM EDT
[#39]
So, you have a small, gallon-sized household water purifier. Use a timer. Back it up with a pressure switch. Whatever you do it will be over-engineered and the turd-worlders will not use it properly anyway. |
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Posted: 2/24/2006 9:13:26 AM EDT
[#40]
.
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Posted: 2/24/2006 9:17:02 AM EDT
[#41]
How's the still coming?
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Posted: 2/24/2006 9:34:22 AM EDT
[#42]
scottryan- You need to give us some more specifics. Is this a batch operation (i.e. you fill it once, boil the contents, then drain to another container, and begin the process again, or is it a continuous process with water flowing into it on some sort of demand?) Do you have electricity available, or close at hand to supply electical control power, or do you even want it? And, how complicated do you want to get with it? (KISS priciple) FITTER had a good idea earlier if you have electicity available.
Mick. |
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Posted: 2/24/2006 9:37:24 AM EDT
[#43]
You could use a conductivity meter, basically two wires spaced a short distance apart. Resistance is measured. No water = high resistance, water = lower resistance. I have used units that can tell the difference from air, water, and hydrocarbon with different audio and light signals. With several sensors you could even determine the water level (1/4, 1/2, 3/4, full) If you use my idea I want 10% of the profits. |
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Posted: 2/24/2006 9:42:29 AM EDT
[#44]
Install a capacitive water level gage. Might have to get one custom made, but it's simple and it's safe.
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Posted: 2/24/2006 9:49:53 AM EDT
[#45]
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Posted: 2/24/2006 10:11:22 AM EDT
[#46]
pay a homeless guy to watch it. he'd probably drink half your product, though.
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Posted: 2/24/2006 10:21:04 AM EDT
[#47]
Check out how canon checks there ink cartridge levels. The put a prism in the bottom, shine a light through it, if the light reflects back you are below a certain level. Must be pretty cheap and reliable, I've never seen one fail.
It would work in everything but the most brackish mix because it works with black ink. This would work if you are boiling WATER in your still and not a mash. -JTP |
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Posted: 2/24/2006 11:54:23 AM EDT
[#48]
steam would cause interferance |
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Posted: 2/24/2006 12:11:10 PM EDT
[#49]
If you are looking for simple and small, wieght of the tank would be the best way to do it. A mechanical swtich could turn the unit off when the water level=weight drops too low.
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Posted: 2/24/2006 12:31:17 PM EDT
[#50]
Ask Schrodinger's cat if it's boiling.
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