Hello, i got a tank that needs a control of liquid level, i was thinking about using an ultrasonic transducer, but my problem is that, when the tank is being filling produces many many bubbles maybe if the tank has 4 meter, 1 meter are bubbles, my question is if the ultrasonic transducer will be able to measure the real level of the liquid?.
In addition the tank is in almost vacuum, the transducer can has problems with this?. Thanks in advance.
Can you weigh it?
The simple answer is it won't work as you desire. A number of years ago I had a similar application but it was to keep a sump at a specified water level by opening a solenoid valve. Upon start up with water being induced to the sump cause a great deal of waves in the tank. Was so bad I thought the relay was going to self destruct. Bad news!!!
The final solution was to insert a 4" dia. plastic pipe in one corner of the sump that extended below the water line. Placed the transducer in the pipe to read the level in the pipe. On initial start there was a problem with the transducer seeing water droplets on the side wall of the pipe and not turning on the solenoid to refill. But after a few hours the pipe would get a coating of water film and the bubbles would be gone. All was well. Would have also helped had I used a bigger diameter pipe but space was limited. I could changed the transducer to one with a smaller sensing range so it would not see the side of the pipe but I was already over budget for the project.
Sooooooo on your project it would be advisable to attempt to do similar with a pipe or a portion of the tank that can be bubble free and wave free and it should work. You may need to experiment a bit................................or a lot.
Good luck!!!
Les
What does "almost vacuum " mean?
Conventionally this is done with a differential "wet-wet" differential pressure transducer that is vented to the airspace inside of the tank and measures the pressure at the bottom of the tank. Did you try this and it didn't work well?
This arrangement will measure the static pressure head in the tank and account for changes in the pressure in the head space ("almost vacuum" or whatever). The height of the fluid above the transducer inlet, h = pressure head/(specific gravity * g) where g = acceleration due to gravity.
Or simply calculate the static head (height of fluid above the pressure transducer inlet) as if it were water and multiply by the specific gravity of the fluid.
A "stilling well" as suggested by Les is a good idea because it will help to dampen the variation in output caused by filling but is not needed to deal with the bubble problem. If the liquid is _extremely_ viscous and the bubbles are substantially supported by the sides of the vessel, the measured amount will be too small regardless of whether or not the transducer is in a stilling well.
You would need to use a "wet-wet" transducer in which the materials used on both the measurement and vent sides of the transducer are unharmed by the fluid being used. Typically the material used is a stainless steel.
There are many, many sources of transducers and associated electronics. If you provide more information on the application, budget and accuracy required, we could be more specific about transducer recommendation. How and when will you use the information? Only while filling?
... Marc Marc_F_Hult
Sorry for my late answer, i have been doing other projects. The liquid is oil and is viscous, the accuracy is not a lot, the height of the tank is 5 meter and an error of 10 cm is perfectly asumible.
So i can use a differential pressure transducer, with one transducer that measures the pressure in the head of the tank and another one that measures the pressure in the bottom of the tank, and with the difference of both pressures i get the heigh of the liquid with this formule h = differential pressure/(specific gravity * g) where g = acceleration due to gravity.
I have been looking for some sensors, and in this page there are some of them.
To calculate the pressure range, i can use the formule.
max differential pressure = h_max * (specific gravity * g), is this correct?
In addition the idea of the pipe was good, but i think that it will be easier the differential pressure.
Finally thanks so much for all your answers, and sorry for my late answer.
I see that this is an industrial application, not home, so I recommend industrial components and mounting of the transducer outside the tank. This will better address the explosion hazard issues the specifics of which depend on the fluid, application and location.
- Yes, that is the equation I provided, but see below for converting transducer output voltage directly to meters of fluid.
- You said that the upper part of the tank would be under vacuum, thus the differential transducer. The 5m of fluid water requires ~=500 millibar ~=
50kP =~7.25 PSI. The nearest higher value offered by Honeywell/Sensotec seems to be the 10PSI differential (~= 70kPa) But see below.- My preference is for 0-10vdc output assuming the associated electronics are nearby.
- So with 10 PSI range and 10vdc Full Scale Output (FSO) the output is
1 PSI/volt = 0.701 meters of water /volt(You'll want to check my arithmetic! 14.7 PSI = 33.9 feet of water = 10.3 meters of water. )
For a fluid with specific gravity of n, the output would be (0.70/n) meters/volt output. For example, for an oil with a sp. gr. of 0.8, the output would be (0.70/0.8)= 0.875 meters oil/volt output.
- The wetted materials of the Sensotec/Honeywell transducers (Hastelloy/lnconel C276 and 316SS) are suitable for any organic fluid.
- You want differential wet/wet as I specified previously.
- My preference would be for 1/4" NPT female fittings on the transducer because this facilitates connection to 1/4"OD x 1/8" ID stainless steel tubing using 1/4" SS-400-6 Swagelock fittings.
I'd make a stainless steel flange and mount two SS-400-1-4BT Swagelock bored-through or SS-400-11-4 bulkhead stainless steel fittings on it and run the tubing through the fittings into the tank. The tube that goes to the bottom should be sealed (pinch it off) at the bottom and a slot cut in it a known distance up. This is so that you can set the tube to a known depth from the bottom (lower it as far as it will go)and still avoid having the input clogged with whatever debris may be on the bottom of the tank.
Then connect the transducer _outside_ the tank at or below the level of the intake on the bottom with additional 1/4"x 1/8" tubing and SS-400-6 swagelock union. Fill the lower tube with oil by drawing a vacuum on it until it siphons out oil from the bottom of the tank.. My preference would be to put a Nupro valve in each line near the stainless steel plate ( = bulkhead) so that I could remove the transducers without disturbing the tank.
Hope This Helps ... Marc Marc_F_Hult
Hi thanks and sorry for my late answers, your explanations are excelent, thanks so much. I have revised your maths and right. I will chose a 10 psi, but the output 4..20ma because the sensor will be far (4 or 5 meters). My problems are with the positioning of the transducer in the tank, i can't make an idea of how the transducer must be placed. Thanks again, and can i do something for you?
explain how to place the sensor. so can you please give me some advice about how the sensor must be place. Thanks again, and can i do something for you?
electronics
Hi,
This is usenet and the intention is to be useful and helpful, so you don't get a bill ;-)
What you can do is let the newsgroup know how your project turned out and any changes or refinements so that exercise is useful to others to (This is customary 'netiquette which, unfortunately, more often than not is not followed any more.)
Some comments:
-- 4-5 meters is not very far, so a voltage output would be fine in nearly all cases. Because you don't need the values more often than about once every second, it would be easy to filter out or average out any noise there might be.
-- Read my previous post carefully again with the understanding that what I suggest is that you put the transducer _outside_ the tank near the bottom. The transducer is connected to two tubes hat go up to the top of the tank along the outside, and down into the tank through a flange (or plate) with the swagelock fittings I described. One of these tubes goes to the bottom inside of the tank. The second tube is open to the vacuum inside near the top to where there is never fluid.
This approach has several advantages including not having to route electrical wires into the tank and being able to install and service without disturbing the tank (if you add valves to the tubes on the outside as previously mentioned).
-- the 1/4" Outside diameter x 1/8" inside diameter tubing I recommended has a metric counterpart as do the recommended swagelock fittings
Hope This Helps ... Marc Marc_F_Hult
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