Level measurement in Silos with powder

[controlnovice]

We're looking for decent accuracy in weight measurement in approximately 30 silos of varying height (3- 30 meters) and width (3- 10 meters. Product is a plastic powder.

We currently have ultrasonics (convert level to weight) and they sometimes work. They don't work very well when filling the silos and/or when coated with product. The ultrasonics are probably 15-20 years old.

Options we've thought of:
Load Cells (too expensive on existing equipment, but most accurate)
Guided Wave Radar (powder may be too light, plus coating may present a problem, but repeatable and higher accuracy)
Laser (issue when filling still, possible coating issues)
Radar or ultrasonic (same problems as existing)

Are the above good for powder filled silos? Any other ideas?

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[IRstuff]

How about a series of pressure transducers up along the inside wall?

If the silage was liquid, it'd be easier, since most liquids are incompressible. Your powder density will vary as a function of height, particularly if the silo is filled. Pressure transducers ought to be a lot cheaper than load cells that weigh the entire silo.

TTFN

FAQ731-376

 

[itsmoked]

I worked at an engineering firm that designed all sorts of stuff. The EE next to me designed the electronics for a system that only did silo measurement.

It was designed for a company called Silomaster.

They work by using a load cell and a hanging cable. The silage always supports the cable starting right at the top of the silage. An empty silo has the sensor mounted at the top. The sensor is a load cell that a cable hangs from and a pneumatic piston. To do a silo measurement the system is installed and the cable weighed. Add silage. When you want a reading the ram retracts a short distant then extends. All the cable below the surface is supported so the only weight is the remaining cable in the air above the contents. The weight directly relates to free cable length. The unit did the math and showed the amount of fill in the silo.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Bindicator was the company.

The SM 5000 (SM silomaster)

Keith Cress
kcress -

http://www.flaminsystems.com

 

[JLSeagull]

Radar level transmitters are the current preference for my recent project. Contact your Ohmart Vega representative regarding the PULS68; or other radar level manufacturer. My notes mention a two-wire 4-20 mA transmitter with a K-band parabolic antenna with swivel flange and four degree beam angle for the ability to measure past fall safety rods to the bottom tangent line of the vessel. This was about three to four years ago, perhaps on HDPE pellets not powder.

 

[tsmith62]

We have had good success with laser transmitters in platic chip and pellet silos. Typically if the laser pointer can hit the level the laser transmitter will work. There are also some special fill and keep features that can be used when filling the silo. Coating issues should be elimibated with a dust tube or dust tube with purge. I would try K-Tek for laser level transmitters.

 

[JLSeagull]

If considering for powder use an explosion-proof flashlight during a fill or dump operation to verify visibility. If you cannot see the level with a flashlight then laser seems risky. We considered laser on my pellet example. The radar preference was based upon client experience at other sites; and laser being outside his comfort zone.

 

[controlnovice]

We have a temporary laser installed to see how it compared to the ultrasonic.

It seemed to track the level better, except when filling the silo, due to the dust. Both the laser and Ultrasonic have problems with the dust and both go to their 'high' level.

I'm looking into guided wave radar, or a low frequency radar (I've read they can 'punch through' the dust issue).

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[glowing]

we use a low frequency radar. Works great. We used to use ultrasonic

 

[glowing]

oh, please note LOW frequency

 

[controlnovice]

glowing: on the low frequency radar, do you have a manufacturer recommendation?

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