Liquid Level Detection

I recently finished the startup on a Waste Water Reclaim System. Most of the system came up rather uneventfully with the exception of the gray water
storage tank. It had a tendency to form froth on the liquid surface. Accurate liquid level detection in this tank is important for stable system performance.
An ultrasonic level detector was factory installed.
It became apparent rather quickly that the sensor was detecting the froth, and the resulting false reported liquid level in the tank was responsible for frequent cycling, and system shut down.
I solved the issue in the short term by installing a large cylinder in the tank, centered under the sensor, with holes in the lowest portion. That allowed system startup, and tuning, to be completed.
My question is the availability of a non-contact sensor that will detect true liquid level through foam, or froth?
Thank you.
Louis-- ********************************************* Remove the two fish in address to respond
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If the ultrasonic sensor is any good, you should be able to adjust it to work through foam. If it's a cheapie preset one, then you need to buy a real one (like www.hawklevel.com or similar)
Why does it have to be non-contact? Displacer-type transmitters will likely be much more reliable in a foam situation.
Cameron:-)
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Radar cuts through foam. On the whole radar seems to be a superior solution.
Walter.

froth,
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Non-contact was a customer spec. As I understand it the owner remembered having problems with material collection on previous contact type sensors.
I agree with you, and suggested a pressure transmitter with an air bleed, but the owner wasn't receptive to anything except an ultrasonic (they were in use in other areas of the plant (in non-foaming environments) without trouble).
Thank you.
Louis
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I would set down with the owner, tell him that the ultrasonic is reading the foam level and ask him what to do. If he says something like "you are the expert", tell him that the expert already suggested a solution which he rejected, so now it's his responsibility to either listen to the expert, hire another expert, or solve the problem himself.
If keeping this job is important to you, write up a report with all known solutions with costs, advantages, and disadvantages, and let him pick one. Or hire me and let *me* tell him that his preferred solution won't work <grin>.
--
Guy Macon, Electronics Engineer & Project Manager. Remember Doc Brown
from the 'Back to the Future' movies? Do you have an "impossible"
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If the water is relatively clean you could use submersible pressure transmitters, alternatively a DP cell. If the water has suspended solids and you have compressed air to hand, you could use the good old bubble tube and DP cell. Also Milltronics make the radar type reportedly good for foam, but I haven't tried them so cant comment.

froth,
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I agree, use either radar or a bubbler. I have had good success with bubblers in river water intake systems where there is trash and such floating on the surface. Of course, if non-contact is a must, radar is likely the way to go.
TZ

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