Sludge Blanket Levels?

Has anyone had success in measuring sludge blanket levels in Picket Fence Thickeners as used in the waste water industry?
I have tried single point level detection using light, very little success with this, and quite often the sensor gets caught in the rake. I am now using ultrasonic and getting better results. This way I get a continuous level measurement. However, blanket level detection is sometimes unreliable. Is there anything better I should consider for this application? TIA
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BIGEYE wrote:

I've asked the staff at my local sewerage authority if that have a suggestion for you. I'll forward a response if it's pertinent.
Jerry
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All the plants I've seen use ultrasonic. Hawk (www.hawklevel.com) make a range of ultrasonic level transmitters for waste-water applications and they're very easy to set up and pretty reliable.
Another option is something from Drexelbrook. They have a wide range of contact-type magnetostrictive transmitters which can discriminate between the blanket and the water underneath and it might be worth talking to one of their reps..
HTH, Cameron:-)
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I'm not familiar with the term "sludge blanket" -- I'm in the upstream oil and gas industry -- but our mud tanks often have an amount of froth sitting atop the drilling mud, making accurate measurement of mud volumes more difficult. In such cases we may use microwave sensors rather than the usual ultrasonic.
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Any info on this?

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BIGEYE wrote:

The sludge blankets I knew formed at the bottom of a settling tank. I haven't heard back from the staff yet. Maybe I'll stop in tomorrow.
Jerry
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Thanks.

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Hi, Have you tried Royce Technologies "Interface Level Analyzers and Sensors"? This is an Ultrasonic sensor suspended under the water surface in a Thickener (usually from the rotating or fixed bridge supporting the rake mechanism). Provides a continues level measurement of the sludge blanket as well as an additional Clarity (opcaity of the liquid) signal. I have used them and had success in wate water / mining (Clarifier / Thickener) applications.
http://roycetechnologies.com /
Regards, Raj

unreliable.
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wrote:

There is standard equipment made for this application from a number of manufacturers. Royce in the US has a reliable product, as does Krohne. Both optical and ultrasonic measurement techniques are satisfactory, but if your sludge blanket interface is not well defined I suggest you use the optical technology as it is a better discriminator of the interface (e.g. in a water clarifier). The ultrasonic is suitable in wastewater clarifiers or in the alumina industry.
Dennis
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