Dual liquid level detection

  • Thread starter Pierre Desrochers
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Pierre Desrochers

Hi all -

We have a series of tanks ( 5 to 8 feet high) wich are filled with water.

At some point Bunker # 2 oil is floating on top of the water. When the level of oil reaches 6 inches we whant an alarm and a second one when it
reaches 12 inches. The total level is varying from 25% to 100%.

We have Warrick dual density float system installed but need to change the system because the float sometimes gets stuck by dirt (leaves, sludge, etc) . We have tried capacitance and press x-mitter but the precision is not good
enough and the capacitance probe gets oily and gives false signals.

10 years ago I work with a ultrasonic level transmitter wich could give a signal for each surface it passed trough... I remember the brand to be "Rexfor or Rexnor" or something like that.

We also tried to clean the actual probe time to time but installation of water jets was prohibitive in this remote location.

Do you have any suggestions on instruments to use to solve this situation.

Pierre Desrochers
Integral Instrumentation Inc.
[email protected]

Ralph G. McDonald, P.E.

We used an RF probe that could detect the interface between Oil and Water to control the water level in an oil skimmer as part of an enviromental upgrade for a power plant.

I could not find the old files on short notice but you might try the following web site:

Larry Kolbert

Two RF probes would do the job very nicely. Sonic gap may be a possibility also. Installation would be on side for both more than likely. Depends on
tank height to some degree.

[email protected]
I've successfully used RF-admittance (straight capacitance does NOT work)for the interface and either Ultrasonic or Radar for top level,
depending on how much vapor from the Bunker oil interferes with the measurement. In this case it sounds like Ultrasonic will work fine for the
top level.

But you also ought to investigate the new phase-tracking radar level as well as RF-admittance, again with ultrasonic as the toplevel. Try Bindicator at http://www.bindicator.com.

Of course, you could use continuous nuclear gauges...they'll work, too.

Walt Boyes

Walt Boyes -- Director of New Business Development
Branom Instrument Co.-- P. O. Box 80307-- 5500 4th Ave. So.
Seattle, WA 98108-0307
Phone: 1-206-762-6050 ext. 310 -- Fax: 1-206-767-5669
http://www.branom.com -- http://www.branomstore.com
mailto:[email protected]

Johan Bengtsson

One (at least theoretical) solution would be to measure the bottom pressure as well as the total level. These two measurements could then be used to calculate the amount of oil. You might have to add a temperature transmitter too in order to
change the density you use for the calculations.

I don't know if this is going to work practically, someone will have to check this against measuring errors and so in order to determine if the sensors give a signal acurate enough to calculate the difference.

the calculations would be based on this:
this is solveable given the pressure level and densities:


The big question is: will it be accurate enough?
Simpler methods might exist, this is only an idea.

/Johan Bengtsson

P&L, the Academy of Automation
Box 252, S-281 23 H{ssleholm SWEDEN
Tel: +46 451 49 460, Fax: +46 451 89 833
E-mail: [email protected]
Internet: http://www.pol.se/
try AGAR who have instruments specially designed for this application (i don't know their web site but Schwing in Germany is a distributor)