Glass level sensor

P

Thread Starter

Paul B

On site we use a mechanical dipping level gauge equipped with an LVDT to measure the level of molten glass (1100 C). Often we have failures, the mechanism seizes due to the heat or glass is picked up by the Pt tip. I remember during my training as instrument tech, it is possible to use a bubbler tube and Dp cell, has anyone used these with molten glass/metal/syrup? What repeatability is possible? Currently the sensor we use is good for 0.1mm.
 
T
You can try radar or ultrasonic level gages for non-contact measuring, or you can weigh the vessel with load cells.
 
I have experience with bubbler tubes. They require constant calibration. if you have to wait long periods of time(More than a year) before you can calibrate it is not the best way to go. the most success I have had with Molten Glass level measurement is with Nuclear gages.
 
In a company I used to work for, we used a bubbler in a hot asphalt tank level device, but suffered considerable problems with coking plugging the tube. It's probably obvious to make sure the "bubbling" gas doesn't cool or chemically react with the liquid.
 
Why do they need constant calibration?
Dp cells have been around for a while, they provide effective measurement for flows etc.
However, the furnace control guy is required to check manualy the level every shift, so long term variations could be overcome.

With respect to nuclear gauges, our site has a strict policy: "I'm not signing that!"
 
W
Bubbler probes have been around since the year dot. Even in the best of conditions, they where a pain to maintain then and they still are now.
Even with newer technology the degree of accuracy will not match your existing method.

If you need that accuracy level, suggest you try to improve what you have.

regards
Wynton
 
Thank you H2O boy for your reply, but I can bubble with oxygen through a Pt tube if required. How accurate was the system before it coked?
 
W
Corning Probes such as you have described have usually been replaced by a gamma nuclear gauge because of the increased accuracy and the fact that Corning Probes foul regularly and have to be replaced, and Pt is not cheap.

Berthold, ThermoMeasureTech, etc. all make these gauges.

Walt Boyes

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to the distribution channel"
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Very accurate, but precision only to .1" (we didn't need more). We used air, 1/4" ID steel pipe, and a glorified fishtank bubbler. Drying the air helped slow the coking, but it was really the cooling of the 350+ degree liquid asphalt in combination with the oxidizing that was the hurdle we never really solved.

It was to be a low-cost solution for a low-overhead industry. Don't know that our experience would transfer to your application, but there it is for what it's worth.
 
Your best bet is a nuclear gauge with a presion of better than .05" possible. Non-contact, non-intrusive. These devices have excellent reliability.

Ohmart is a possible vendor to look at.

L.Kolbert
 
J

John G. Boland

Hi Paul,
Molten glass is a terribly hot nasty sticky corrosive mess to measure with contact level sensors, as you have experienced and other posts have substantiated.

A nuclear source and 20mm (vertical dimension) detector are a largely maintenance free system to measure molten glass level with high resolution.

The detector output may not be linear with glass level if the detector axis is horizontal and its cross section is circular. This is not an issue if the objective is to control the glass level to, say, +/- 0.5 mm within a narrow range of +/- 1mm and less accurate measurement of occasional +/- 5mm deviations is acceptable.

The non-linearity, typically a tangent curve shape for a circular cross section detector, can be largely calibrated out if absolutely necessary.

The detector must be water cooled. The source may or may not need cooling depending on the furnace / channel design.

Foundation Fieldbus or Profibus devices provide higher resolution measurement data and access to many measurement parameters and status flags "for free" - that is, without additional interconnecting wiring to a PLC/DCS. NOTE TO ALL: This is *not* a fieldbus war taunt. Puhleeeez.

I have heard that laser reflection level detectors work well if the surface of the glass is *never* foamy... but have not used them. Cooling advisories still apply.

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we use a mechanical dipping level gauge equipped with an LVDT to measure the level of molten glass (1100 C). Often we have failures, the mechanism seizes due to the heat or glass is picked up by the Pt tip. I remember during my training as instrument tech, it is possible to use a bubbler tube and Dp cell, has anyone used these with molten glass/metal/syrup? What repeatability is possible? Currently the sensor we use is good for 0.1mm.
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Best,
John G. Boland, president
Strateg!c Method$ Corporation
One Parker Square Suite 408
2525 Kell Boulevard
Wichita Falls, Texas 76308
940.322.9922
940.723.1478 fax
 
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