Fluid Level Detector - Control Circuit

In a typical application where the device is employed for sensing low water levels in a tank, a simple steel probe may be inserted in the top of the tank with the tank grounded.

Could you use a simple stainless steel probe?

Indeed , as the distilled water is almost nonconductive we can not use a resistive probe. In this case you can use a capacitive or ultrasonic transducer but this is an expensive solution. A more simpler and cheaper mode would be a switch flotor like those used at the submersible water pumps.

If I understand your application correctly, you don't need to sense all levels in the tank, but only if the level is above or below a specific level in the tank. How about a cheap bilge pump float switch from a boating store? You can also check McMaster Carr online, they sell a number of float style level switches (including Stainless steel sensors). Or if you are measuring the level in the overflow reservoir (not the active tank) you could simply use a pressure switch. Water is approximately .5 psi per foot of depth. Get a cheap switch in the range you need. By the way, I have even seen toilet tank valves that use pressure switches, and they have to be accurate to .5" of water level.

Hello,

I have refered to the following website to understand how fluid level detection will work

http://www.fluidswitch.com/pages/appnotes_2_inc.htm

May someone please explain to me how the provided mechanism works.

Thanks

Gyandeep

They have given you a very nice schematic to use after you buy the sensor. The diagram shows you their sensor, labelled "switch". Detecting fluid is easy enough, gets less easy as you impose boundary conditions. Is this a project just for fun / education? If so you can cheat. If its for real life, better get real and either pay for a decent sensor or develop something clever. Think fiber optics.

doug

What is the variation of the water level? you can use an ultrasonic transducer or absolute presure sensor with a tube to detect the water level.

the image on the left will start pumping when the bottom float switch closes and keep on pumping till the top float switch opens. (pump up)

the image on the right will start pumping when the top switch closes and stop when the bottom switch opens. (pump down)

Use an optical level sensor instead, when the fluid level rises up the face, it will change state and provide you with the signal. No moving parts, and the interface circuits are straight forward. Try GEMS or a similar type.

Al

For your problem I suggets please contact "Sapcon Instruments Pvt.Ltd 131,Palshikar Colony,Indore-452004 ( M.P.) India" . They are one of the leaders in all type of level controls and level measurment instruments manufacturing in India.

Mail: sales@sapconinstruments.com or sales@sapcon.in

Web Site : www.sapconinstruments.com

Just put two SS rods parallel to each other, insert those to full depth of water. As water level increases the cpacitance between these two rods (working as electrodes)changes. Use this value as measured value. Build a circuit with this capacitance as measured value and other value as set point. You can detect the level easily.

I hope you will need no information for the suitable circuit.

"As water level increases the cpacitance between these two rods (working as electrodes)changes. Use this value as measured value. "

The capacitence type gauges available commercially use a thin walled tube with a wire running along it's central axis. Insulated spacers insure that the wire does not touch the wall.

As the level of fuel oil (or gasoline) rises, the capacitance changes, just as you discribed, and this change is converted into a gallon or liter read out.

This type of sophistication is not needed. He simply wants to know when a certain threshold of volume is reached.

It would not work anyway, not in a tank with water, as the water will short out the leads and render the device useless. In fact, commercial manufacturers of capacitance type fuel gauges, use this phenomenon to set off an alarm that alerts the user of water in the bottom of the fuel tank.

My plane is equipped with two such probes, one in each wing tank and it is used just as described. This is a critical safety issue as many aircraft operate at altitudes where the lapse rate has lowered the outside temperature below the freezing point. Water that stays as water might not harm anything but a plug of ice can obstruct fuel flow and shut down the engines.

Capacitance measuring systems for liquids are great but alas, I seriously doubt it will work in this application.

L.J.

Thanks Jaguar

Capacitance measuring systems for liquids are great but alas, I seriously doubt it will work in this application.

I agree with you that open wires in water will short. But I do not agree with your above statement. I am using a system based on capacitance measurement for water level detection. If one of the bars is insulated, we can avoid shorting.

I can not spare additional details of the system and the circuits as it is propritory information, but let me tell you, the switching action takes place withing 50 microns of set level repeatedly in my water level detection system.

Try IFM Efector they have a level sensor that has four programmable settings.

http://www.ifmefector.com/ifmus/web/home.htm

I developed a simple, inexpensive switch for network monitoring of water in critical heating plants.

The device consisted of a short section of 2" (?) PVC, covered at the bottom with flyscreen, held in place with a hose clamp.

Inside was an ordinary ping pong ball to which I'd secured a magnet with silicone.

A PVC cap was drilled and fitted with a simple sealed reed switch and then glued to the top of the pipe. A second hose clamp secured the completed assembly to a section of 1 inch PVC and allowed for adjusting the height inside the well.

If water entered the assembly through the screened opening, the ping pong ball would rise, close the reed switch sending a low voltage signal to the communications board.

Note: size the ID of the pipe to the ping pong ball. You want a close fit but loose enough to allow movement. When inserting the ball/magnet, insert it with the magnet on top so it's closest to the reed switch. If the application is critical, you can insure floatation redundancy by securing a second pin pong ball.

Simple. Effective and I was able to produce 50 of them for a per unit cost of about $3.00 plus labor, which wasn't much as I'm sure you can appreciate from the simplicity. Obviously, materials are readily available

L. J.

Have you thought about using an ultrasonic meter , it measures the distance between the top of the tank and the fluid top and caculates the level. Here is a link to one , maybe you could modify this to work for you.

http://www.liftandlube.com/product_p/gra%20119274.htm

If your tank has both hydrogen and oxygen (oxyhydrogen) in it, as you say, then you would want to take several measures to insure that there is no possibility of a spark from an electrical circuit, static electricity buildup, hammering, drilling, grinding, etc. Pure, or nearly pure, hydrogen in a tank is almost as safe as many other highly flammable gases, (although unlike other gases, it leaks through the walls of steel tanks) but the combination of the two gases in a tank is a bomb just waiting to go off.

In industrial situations where there is a reasonable likelihood that explosive mixtures or gases might accumulate, explosion proof (and/or intrinsically safe) equipment and techniques are used. This equipment is expensive for obvious reasons. Your situation, if it is as you describe, is much more dangerous, because the mixture is always present in the perfect explosive ratio. You would need to take extraordinary measures to make a tank of oxyhydrogen reasonably safe.

Better to accumulate the gases in separate tanks -- but even then, hydrogen must be handled with great care, because is has extremely wide explosive limits -- from 4% to 75% (by volume) in air.

Optical sensing (via fiber optics, with the electronics outside the hazard area) would make sense, regardless of the accumulation method (single tank or two tank) employed. There are many methods of optical level sensing (detecting an opaque float, detecting the displacement of an angled beam reflected off the liquid surface, etc.

Hello,

if you don't need to know exactly the level of water I would suggest you use only a switch with a floating ballon to activate / deactivate a power circuit

Blink is of course correct. Thats in fact why I asked if this was for fun or for real. This environment is UL Class 1 Div 1 Kaboom. You need to have an intrinsically safe circuit and sensor. Fiber optics is often the best but there are other good solutions. Nobody in their right mind is going to hand you a circuit to do this, nor should they. If in fact this is just for fun, then try anything cheap like the floating ping pong ball, which seems fun.

You can use float switches in series with whatever components you are using. The float switch is usually suspended on the end of a tube or plastic pipe. The switch itself is basically a cylinder with a floating donut around it. The cylinder has a magnetic switch inside it, while the floating donut has magnets in it of course. Anyway when the water comes up to your predetermined level, the float floats up higher on the cylinder and hits the switch. The position of the switch depends on the way you have the cylinder oriented. One way may be normally closed, whereas if you flip the donut, it becomes normally open. I have worked with these switches in a similar way you have described and they work well.

One example can be found at www.aquahub.com/store/ifloatfloatswitch.html

This may have been somewhat confusing, but once you see the picture you will understand

This is definitely not an application where you want to purchase just any type of level switch. Even without all the details of your process, I would imagine you're looking at a process that would carry an NEC, NFPA, electrical rating of CLI, Div I or Zone 0 for the interior and a bubble around any vents. There would also be a bubble around the tank, which would carry a lowered classification ex: CLI, Div II. You might want to ck out www.gemssensors.com or www.drexelbrook.com They both have good tech support groups, which should also be of some help in your selection of the proper device. Be safe!

Use a Flygt ENH10 Level switch simple 100% reliable cheap can be used in any liquid and safe in Zone 1 areas. Available from any electrical wholesaler or ITT pump company world wide.

Mount your tank on load cells. As the water enters the tank the weight will increase. There will be no circuits needed in the tank. Monitor the weight and trigger your stop signal off of the ideal weight of the tank full of water. All electronics isolated.

Hi,

if your tank is not metallic you can put the capacitance electrodes outside.Simply attach to the wall two wires (I used HF flat ribbon cable that comes with two conductors and a distance of 8mm) squeeze the insulation a bit to insulate the lower end and attach to the upper end the simplest known capacitive transducer: one Schmitt-trigger inverter, the output fed back to the input with a resistor and the capacitance to input and ground. As there are 6 of these inverters in one ACMOS or HCMOS circuit use one as output buffer and two more as a reference oscillator. Oscillation frequency will be determined by the Schmitt-trigger hysteresis and the RC time constant.

You need an additional not too bad DC power of 5V for ACMOS and a frequency to switching point converter as a frequency difference detector,

Or simply use the frequency to determine the setpoint.

RHABE