# Level measurement in silo of corn by load cell

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Dear Automation friends

I have a silo of corn with 10m radius and 20m height. I want to measure the level of corn in the silo by putting a load cell on the floor of it and measuring the weight of corns column above the load cell and estimate the level of corn.

Due to frictions between corn and body of silo, there is some non-linearity effect in the measurement but I think, in respect of relation between dimensions of silo this non-linearity is negligible. Is this a true assumption or not? If not, in which way I can use a load cell for my measurement.

best regards
M. Afazeli
Project manager
[email protected]

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#### Eric Simmons

level of corn....
I am not an expert on load cells, but have some experience in there use. After thinking about this for a little bit i thought perhaps you might want to try a diferent aproach to your measurements. I.E. using an infrared prox avery half a meter or so up the side of the silo. the reason i myself would stay away from the load cell is because of calibration of the device, it would seem like quite a chore to have to empty the silo to perform a routine calibration. once a base formula is established that say every half a meter equals 1k of corn then you plc could then equate that the level of corn is filled to 7 meters inside the silo...therefore you have 14k pounds of corn on hand....
"just a thought" I hope i didnt waste you time with this reply.

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#### Vitor Finkel

By using a load cell you will be actually measuring the weight of the corn. If you really care for the level, and not the weight, corn density ( associated with it's moisture contents ) and geometric "cone" formation due to last loading or unloading operation will be your main sources of errors. I have no idea of what errors
you may experience due to friction between corn and silo.

Vitor Finkel

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#### Vega M. Hernan M.

Why don't you use ultrasonic level meters?
It is linear and without installing problems. You can use Endress and Hauser, Milltronics, Vega, Hawk, etc.

Atte, Hernan Vega

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#### Walt Boyes

I'd contact Kistler-Morse in Bothell, WA USA for a loadcell type measurement, but I'd also contact Alliant/Bindicator http://www.bindicator.com for their radar level systems.

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]
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#### Blunier, Mark

I don't think it will work. In the design of silos, the walls carry a significant amount of load. As silos get taller, the weight on the floor will not increase - its carried through the wall. You are probably better off using a sonic or radar level transmitter.

Mark Blunier
Any opinions expressed in this message are not necessarily those of the
company.

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#### Hugo Ahrens

No chance this will work. I tried something like this with feed pellets in a smooth metal wall silo (a lot less friction than the usual concrete) and had to give up. All you will measure is the small cone of material above the
disk tied to your load cell. The civil engineering types have a name for the pyramid shaped support structures that build themselves in the material (I forgot, it was some twenty years ago).

Hugo

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#### Matthew da Silva

Since I had nothing better to do, I searched a while and found these links, if you're still interested. Also, what Mark Blunier said.

http://www.lundahl.com/application_notes/dcu1100/bsm.html -- ultrasonic sensor
http://www.deltacnt.com/solids.htm -- mechanically-operated plumb
http://www.levelandflow.com/product/solids/index.html --
piezoresistive vibration (but descr. is for granular powders) -- Also, microwave
http://www.barton-instruments.com/levelscan_hot.htm -- ultrasonic
http://www.barton-instruments.com/catalog_mis.htm#inventorymgmt --
ultrasonic, others
http://www.chemicalprocessing.com/protected/cp699/equips.html --
http://www.isa.org/journals/intech/brief/1,1772,259,00.html --
http://www.aaliant.com/tank_level/rp9000/rp9000.htm -- microwave
impulse radar (dielectric constant greater than 5)
(dielectric constant greater than 2) but Insatech also has other methods incl. ultrasonic, vibration, electromechanical etc.
http://www.hitechtech.com/ultrasonic.htm -- ultrasonic
http://www.hitechtech.com/soniclas.htm -- sonic laser (manufacturing
is Nivelco, a Hungarian firm)

I also located a cool site about dielectric constant at
http://www.merix.com/resourcecntr/materials/dielectric.html

My personal feeling about these MRI devices is that they will be costly to purchase and expensive to maintain. According to the explanation from Merix, they should have no trouble measuring your corn inventory, which
is fairly dense, and since humans have a Dk of around 60 (again, says Merix).

There appear to exist many options, but the Hitech company seems least expensive and has a wide range of products. Of course, you may prefer to use proximity sensors, as Eric Simmons suggests. That seems to be low-cost, but installation would be fairly involved and maintenance might be a problem due to sensors knocked out of whack etc.

Matthew, Tokyo

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In order to measure level, you can use Microcells, manufactured by Kistler Morse, within the US. The cells can be located to measure
stress not only vertically but horizontally as well. To install them you do not need to cut the legs of the silo, but only to make a couple of holes with hand tools. You can check kistler morse
website.

Jimmy Saldivias

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#### Johan Bengtsson

If you want to measure the weight (not the level), why not just put the load cell below the entire silo? Built in a smart way it could be possible to temporarily remove it for calibration
if necesary and the weight of the silo itself should be faily easy to subtract from the readings. Perhaps you will need more than one

Just a thought...

/Johan Bengtsson

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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/
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#### Larry Kolbert

You may want to consider laser level. It is mounted on the top of the silo, is non-contact measurement technique. Performance is +/_ 5mm to the point of measurement. Unlike sonic and radar level, angle of repose does not affect measure as laser beam is extremely small.

Go to TN-KSI.com on the web for more info if you choose.

L.S. Kolbert

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#### Fred Chwalek

Good luck using sonic or radar. The top of the corn will not be level, there will be dust in the air, this will add to the difficulty of reading
the level correctly. You might look at Milltronic's (?spelling) ( I think they claim to be able to do this ). The best way is to place your load cells under the vessel, not an inexpensive retrofit, but maybe not too bad
for a new installation. I looked into this a couple of years ago, and certain ultrasonic level measurement people wouldn't even touch it.

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#### Walt Boyes

Larry, this is critical to the measurement. Can you explain in more detail how angle of repose doesn't matter to the laser device? It seems to me that it would be impossible for it not to matter...

If it is a matter of beam scattering, I could see it not mattering, but how do you use a very narrow beam and then estimate material level with a steep, or shallow angle of repose, and it not matter?

We all see these nasty applications daily, and it would be cool if there were a new tool that really did work better.

Walt Boyes

--------------------------------------------------------
Walt Boyes -- Director of New Business Development
Branom Instrument Co. Factory Representatives
5500 4th Avenue South, Seattle, WA 98108-0307
1-800-767-6051 fax: 206-767-5669 direct: 206-577-3310
email: [email protected] http://www.branom.com
--------------------------------------------------------

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#### Rufus VS

It sounds like a load cell will only work if it is weighing the silo as well as the product
inside. In my ignorance of silo operation, I might suggest an inner cylinder on the load cell to hold the product?

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#### Kirk S. Hegwood

I have worked in the rock crushing industry a number of years - marble, etc. - and Milltronics seems to have the best level measuring device. Same conditions as corn is seen, very dusty, pneumatically conveyed and the top is not level. The hardest part whether it is sonar or weigh scales, is the calibration. Which customer can fill their silo then empty them for accurate calibration?

Kirk S. Hegwood

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#### Al Werner

Dear Contributor:

I have for many years now designed ultrasonic level gauges for breweries, to measure both grain and liquid levels in very large storage and brewing tanks.

If you can tell me a little bit more about your application, and the required accuracy of the measurement I would be delighted to assist you.

Kind regards

Al:

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#### Larry Kolbert

With pulsed laser, measurement is to the point of beam contact. As long as something is reflected back, that point of contact is measured. The laser
beam is .28degrees. Scattering is minimal. Measurements with pulsed laser have been made on coal as well as polyethylene pellets and grain. System software allows the equipment to handle a wide variety of products with dusting conditions successfully. Distances/levels measured have been out to 130 feet on the mentioned solids.

If there is a difficulty w/solids measurement, it will be determining material volume as angle of repose varies. In many instances, that problem
is minimized due to fact that other technologies are more difficult to apply to many solids applications with setup being difficult and results questionable. Laser is top of vessel mounted, non-contact and non-intrusive.

It is my understanding that making a measurement at 1/3 the diameter will generally give a user reasonable expectations of average level in the
bin/silo. Not being an expert on solids level measurement, I only relate this as information related to me on more than one occasion. Perhaps others can confirm this being true or invalid information.

Laser experience indicates that a system can be easily demonstrated on many applications to determine viability of measurement w/o costly
installation effort only to find out device is not suitable.

Larry Kolbert
TN Technologies
Kay/Ray Sensall

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#### roger Irwin

"Blunier, Mark" wrote:

> > Due to frictions between corn and body of silo, there
> > is some non-linearity effect in the measurement but I
> > think, in respect of relation between dimensions of
> > silo this non-linearity is negligible. Is this a true
> > assumption or not? If not, in which way I can use a
> > load cell for my measurement.

Stick it right underneath so it gets all the weight.

> You are probably better off
> using a sonic or radar level transmitter.

What sort of reflection will you get off a cone of corn?!

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#### Vega M. Hernan M.

We use ultrasonic level meters in silos of mineral and dust is present all the time. With new developments, actually dust is not a problem. Also you can ask for a test (we did it) and see if it works.

Hernan

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#### Roger Irwin

> Built in a smart way
> it could be possible to temporarily remove it for calibration
> if necesary and the weight of the silo itself should be faily easy
> to subtract from the readings.

Just hang known weights to the outside to calibrate. You do it first with the silo empty, to test linearity at the bottom end of the scale, then, with the weights attached, add grain till you are at max load and then remove the weights.

> Perhaps you will need more than one