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oil-water level measurement

oil-water level measurement

Hi All,

can anyone give an advise for a level instrument which can handle oil and water level measurement with the presence of emulsion layer?

as f as i know, Guided radar level transmitter work well when there is no emulsion layer in between oil and water layer. is there any level instrument which can measure top of water level and top of oil level and neglect any emulsion level?

Kind regards,

RE: oil-water level measurement

I assume you are looking for Interface Level
Differential pressure is what we use, either flange mounted DP or in special cases bubble tubes.
Displacers are quit often used
I have been working on a new type but I would need to know more about your application.

RE: oil-water level measurement

Let me get this straight in my head.  Harseko has a column of fluid with some amount of water (probably known density), some amount of oil (probably known density), with an emulsion layer (probably unknown density), and you can use a dP to determine the interfaces?  That is truly amazing.  For any given dP, I can come up with an infinite mix of the three substances that satisfy the dP.  Even if the density of the emulsion was known, the answer is still one equation with three unknowns.  

I don't think I'm buying that one.

Some of the new guided-wave devices seem to do a pretty good job at determining a clean interface between two fluids with different densities (and they seem to work equally well when the densities are pretty close or quite far away from each other).  The problem they all have with emulsions is that emulsions are nearly never homogenous and you don't get a clean interface--you just can't rely on the level that it selects from inside the roiled-up section.

I've never been able to let a device pick that interface--hell, even having a person read a sight glass isn't a lot better since I've rarely had an operator truly believe that paralax was an important concept.


RE: oil-water level measurement


thanks for the comments.

Roydm, At this point I have similar opinion with zdas04 (David).
Total liquid level measurement is still doable with DP transmitters.
However, interface level..probably not yet..

no solution yet for this issue?
need help!


RE: oil-water level measurement

Check with a company in Texas called Entech Design. They make ultrasonic level meters which detect interface layers.

RE: oil-water level measurement

Now hold on there a minute.
I didn't say I could measure both interface levels, oil to emulsion, emulsion to water
But I certainly can measure the average interface level, we do it all the time with DP
and with good accuracy.
in fact we have tried just about every other form of interface level known to man but keep
reverting back to DP and bubble tubes because that's all that will stand up to the process.

As I said I am also investigating a different technology that will tell the interface level to about 1/2" but I'm not about to divulge it here.
No it's not radar, sonar or anything close.

RE: oil-water level measurement

Sorry I will have to post again, am I the only one who can't find the edit key?

The emulsion layer is nothing more than a mixture of the other two layers.
For the sake of argument Oil SG = 0.9 and Water = 1.0
If you were to look at a cross section you would see
SG   Component
0.9   Just Oil
0.9   Just Oil
0.92 water droplets in oil
0.95 more water in oil
0.97 oil in water
0.99 oil droplets in water
1.0  Just Water  
1.0  Just Water                             (I'm trying to show the emulsion is not homogenous)

leave it a while and the two layers will normally settle out into just two components.
Since the emulsion layer is a mixture of the two the average density is mid way between say SG = 0.95

The emulsion layer might be quite thin or quite thick but the whereabouts of the mid point 0.95 is quite easy to figure out using a DP transmitter.

As you point out GW radar can work for a clean interface (well defined change in dielectric constant) but a thick emulsion layer will absorb rather than reflect. (that may not be quite correct but it's how I visualize it)

RE: oil-water level measurement

I will have to agree with roydm on this one and thanks for quick specific gravity lesson. Zdas04 the DP meter is the common choice for interface levels. The other common choice are displacer levels, the old mechanical prehistoric reliable means of interface measurement. Radars are percieved as reliable, technically advanced and of course best for any type of level measurement. Radars are so sensitive to their environment. At times if the the water di-electric constants change to less then 2.5, your radar is useless. You have to tweek your radar most time to operate beyond its capability in order for it to work, this all depends on the di-electric constant of the product. Radar folks are still working out the gaps in there latest and greatest. All a DP requires is a full vessel, the media that will be measured, such as the oil for a oil and water interface and a control board operator that will not upset the environment of the vessel. All these devices have the same weakness. The weekness is an emulsified if there is such a word, vessel (Unit upset, oil and water mixture thru out the vessel). The calculation for DP interface measurement is easy. If you are able to use actual media. You would fill your chamber with oil, set your LRV. Fill the vessel with water, set your URV and you are done.

SP1 (Oil) X Measuring range = Upper Range Value (URV)
Sp2 (H2O) X Measuring Range = Lower Range Value (LRV)
URV-LRV = Span

Hopes this Helps


RE: oil-water level measurement

Hi All,

The explanation is getting more make sense to me. Thanks.
Shall we go to an example?
For instance there is a horizontal vessel with 1 meter diameter with a process running through this vessel. When process stop, clear water and oil stay in the vessel with level of 0.4 m each. During the process, this vessel then contain, say, 0.3 m water, 0.1 meter emulsion and 0.3 oil.
How could DP cell (1 DP cell?) be used for this level measurement?
Let's assume bottom of vessel (0 m) is used for high point of DP and at level 0.9 as low point.
How can one apply the URV-LRV with its measuring range?


RE: oil-water level measurement

Your description is a little confusing.

It sounds as though your tank overflows out over a weir or a nozzle at the 0.4+0.4=0.8 meter level but then when you are running it drops 0.3+0.1+0.3=0.7
And then to add to the confusion you connect the LP at 0.9

Are you trying to measure interface level,  total (true) level or both?

I am not going to suggest how you might do it until you post a sketch, tell us what you are trying to do and give the specific gravity of oil.



RE: oil-water level measurement


Check the Servo Type level transmitter such as Endess+Hauser model NMS5.

RE: oil-water level measurement

What is really interesting about the oil water emulsion is the conductivity and what I call the memory effect.
As oil drops mix with the water the conductivity drops (oil droplets in water) then all of a sudden it becomes an insulator (flips to water droplets in oil).
Some of the fluids I tested seemed to flip from conductive to insulating at one concentration then switch back at a different concentration about 20% difference so you get sort of a deadband where it can be conductive or insulating. If left to settle out in one state when they are mixed again they go back to the state they were in previously (I call this memory)

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