Level Measurement in Jugs

  • Thread starter Kirk S. Hegwood
  • Start date
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Thread Starter

Kirk S. Hegwood

Greetings All, I'm working on a small machine which will require the level measurement of liquids. All I need is an input as to appropriate level and/or if the container holding the liquid is empty (prefer level). The input will be 12VDC and tied back to a PLC. I've tried to just use the conductivity of the liquid (two bare ended wires immersed) for the level, but the liquids vary in consistency (thin & thick) and chemical makeup. Especially the thick chemical (clings to wires and still allow conductivity) doesn't allow this idea to work. Thin chemical is perfect for the application. Any ideas or thoughts? Thanks in advance, Kirk S. Hegwood President Signing for Hegwood Electric Service, Inc. [email protected] Phone: 770-447-8853 Fax: 770-447-5310
 
Ultrasonic would work also. If little amount of air is no problem in the fluid, bubbler tube would be lot simpler (if you have compressed air sufficiently clean). Load cells would be ideal, but more expensive.
 
Hello Kirk We can probably build a small level switch for you in either continuous or point control. Output can either an on /off switch, resistive or 4-20 or visual. (in order of cost) It sounds like you only need a low level alarm. The multi level small would do it. It can be from 1 to 4 stations - a 3/4 or 1" D float can be used. If the liquid is thick - a larger ID float hole is used on the small tube. The switches are rated to a max. of 240 V @ 0.5 amps resistive. For future applications - your idea of two wires is great - but over time, if it worked, the wires will get a very slight buildup and possibily arc within itself. Sometimes an arc is not good in chemicals. Thanks Bob Hogg http://www.almegcontrols.com/
 
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Anthony Kerstens

Opaque, translucent, or clear jugs. Maybe photo eye or capacitive prox exterior to jugs. Anthony Kerstens P.Eng.
 
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Kirk S. Hegwood

The jugs are opaque. Using electronics would be cost prohibitive. There has got to be an inexpensive simple application...I hope. Kirk S. Hegwood President Signing for Hegwood Electric Service, Inc. [email protected] Phone: 770-447-8853 Fax: 770-447-5310
 
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Kirk S. Hegwood

JMGiraud wrote: Ultrasonic would work also. [Kirk S. Hegwood] Yes, but this is a comparatively inexpensive machine and with eight to nine jugs per machine, would be cost prohibitive. If little amount of air is no problem in the fluid, bubbler tube would be lot simpler (if you have compressed air sufficiently clean). [Kirk S. Hegwood] Unfortunately no air is available. Load cells would be ideal, but more expensive. [Kirk S. Hegwood] Agreed.
 
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Joe Jansen/ENGR/HQ/KEMET/US

Try one of many different models of ultra-sonic sensors. Non-contact. Works great. --Joe Jansen
 
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Loran (Buddy) O'Neal

Two possibilities I can think of: 1. Weigh the container with load cells or something similar. If the container has a known area and the fluid has a known density/specific gravity then the amount in the container can be calculated. 2. Use a distance measuring ensor, mounted on the top of the container, to measure the distance from the top to the fluid. I think Keyence makes IR devices like this, but you'll need to verify what elements will properly reflect the signal to the sensor. I hope this helps. Good Luck. Buddy O'Neal Elipse Software Corporation [email protected]
 
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John G. Boland

Hi, Sorry that I did not see the original post - please excuse repetition or irrelevancy. A couple of thoughts, if a billionth of a percent accuracy is not required: Depending on the wall material, a jug sounds different if tapped when full than when less full. Some of us grew up playing spoons and blowing on jugs, tuned by water level. OK, compressed air is not available... perhaps a cheapo fan could blow across the mouth of the jug, or hmmmm... the filling stream may generate a sound whose frequency is related to the level - happens when I fill a bottle in the sink. Is the jug wall thin enough and the filling liquid different enough in temperature from the jug / environment that a fast response contact thermocouple could pick up the level as it rises? Perhaps a multi-station infrared sensor system would be cost effective. Regards, John G. Boland, president VisiBit Corporation www.visibit.com One Parker Square Suite 408 2525 Kell Boulevard Wichita Falls, Texas 76308 940.322.9922 940.723.1478 fax
 
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Anthony Kerstens

Inexpensive eh. How about a mechanical counterbalance with a limit switch. If you need a different volume, you adjust the mechanical arm length. Anthony Kerstens P.Eng.
 
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Hello... If you were to close the opening in the jug with a tapered plug you could then fill the jug by means of a fill pipe through the plug. A second pipe through the plug connected a to a small precision flow meter would show you the amount of air displaced by the chemical. The volume of air displaced would equal the volume of the injected liquid... Just a thought but why would this not work. Best Regards... Rick Kelly Chief Electrical Technician Natural Cuts Cheese Operations Kraft Canada (613) 537-8069 V (613) 537-8057 F [email protected] http://trondata.on.ca
 
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Kirk S. Hegwood

The material is being drawn from the jug. We would like to know when the liquid reaches a certain level to alert the operators they are low. Using a tc or ir would start bringing in expensive electronics. This is "supposed to be" an inexpensive machine.
 
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Kirk S. Hegwood

I believe I may have to go this way. I've seen this done on some other machines, which was a terrible setup, but maybe I can improve it. Kirk S. Hegwood President Signing for Hegwood Electric Service, Inc. [email protected] Phone: 770-447-8853 Fax: 770-447-5310
 
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Kirk, Given your parameters, I would fool around with using a SINGLE wire hooked up to the input of a CMOS gate (inverter). You might have to bias the input with a VERY high value resistor, but once you figure this out, the wire hitting the liquid should be able to consistantly change the output. You'll have to protect the input also, maybe with some zener diodes. If you want to mess with analog, it would be better to use an op=amp or a comparator, but I used a similar arrangement for a non-contact prox sensor (another application where there was no room for the price of an off-the-shelf sensor) and it worked fine. That way, you have six input channels for about 15 cents. You may even be able to run the CMOS off 15V and run the PLC input directly. Don't you have to clean the goop off the wire in between jugs? Or is this a static appplication, where the wires just sit in the jugs? Willy Smith Numatics, Inc. Costa Rica
 
Just a thought, If all of the jugs are equal in weight, then a sensitive weight scale from a company like Ramsey could work to detect level. Ray Yuzna
 
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Joe Jansen/ENGR/HQ/KEMET/US

There have been many suggestions that seem to be exercizes in creativity, rather than a cheap method of getting a level. I do not know manufacturer, but I have worked with devices that consist of multiple reed switches enclosed inside a tube, with a float that rides up and down the tube, with a magnet inside to trigger the reed switches. This gives reports of various levels, although you have to be careful of float size and reed placement to try to eliminate the dead spaces in between where you get no reading. As I said, I no longer have the details of these things, but perhaps someone else has heard of these??? --Joe Jansen
 
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Kirk S. Hegwood

It probably would work. But this is the challenge...keeping cost low. With your idea, it would call for 8 precise flow meters at $X and they would have to tie back into a high speed counter card. It raises the price too high.
 
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Hi guys, As always the question "What will do the job?", fails to be answered with "What is the job?". People try to answer an unspecific question, not having nearly enough information to give a conclusive answer. Everyone having their own idea of how much is too much money to spend. Eight people give a reply without knowing what the measurement will be used for. Having no idea of the required accuracy, no concept of the process or how it is controlled, we don't know if the process fluid is explosive, corrosive, toxic and yet ..... we know an instrument that will do the job :) This guy could be a kid trying to distill "wood alcohol" and one of you told him to put a bare wire into the jug :) Jovially, Richard King. Alesa Alusuisse Engineering Australia Pty Limited. Phone: +61 7 3218 3555 Fax : +61 7 3236 0155 Email: [email protected] Web : http://www.alesa.com.au
 
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Michael Griffin

<clip> >The jugs are opaque. Using electronics would be cost prohibitive. There >has got to be an inexpensive simple application...I hope. <clip> You're going to make something that's cheaper (installed) than a capacitive prox? What exactly is your target price per jug then (including engineering, fabrication, installation, etc.)? Even if you were going to make a contraption out of springs and micro-switches (to weigh the jug), you still have to design, build, and tweak it. ********************** Michael Griffin London, Ont. Canada [email protected] **********************
 
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Robert D. Wagner, P.E.

Hi List: If the draw tube is flexible the following may be a cheap and dirty solution. Add a fixture alongside the jug so the jug can rest against it at an angle in a quasi-stable position. Add a mcroswitch with lever to the fixture. Add a spring attached to a support with a screw eye on the other side of the jug, diametrically opposite the fixture. Fashion an attachment mechanism (clip, loop etc.) as required to attach the spring to the upper area of the jug. Adjust the screw eye and the rest angle to provide sufficient tension. When the jug empties, the spring will pull the jug to a vertical position and the microswitch will close or open as configured. Nothing elegant but definitely low cost. Robert D. Wagner, P.E. Robert D. Wagner, P.E. and Associates
 
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