Level measurement in silo of corn by load cell

> From: roger Irwin [mailto:[email protected]]
> > > 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? ...<clip>
> Stick it right underneath so it gets all the weight.

If the silo is supported on load cells, the bottom of the silo would need to be built heavier to withstand the point loading, as opposed to the setting the silo on the ground. I doubt if it would be practical.

> > You are probably better off
> > using a sonic or radar level transmitter.
> What sort of reflection will you get off a cone of corn?

Another thing to keep in mind, is the cone points up when it is loaded, and down when its emptied. On large silos there may be multiple loading and undloading points, creating multiple cones that aren't centered. We grind 120,000 bu of corn a day at the plant. We don't use level transmitters on the corn silos. While there are some transmitter out there that will work, its easier to keep track of how much was put in and taken out than to try to rely on a level transmitter. We have high level probes so we don't overfill on accident. For monthly inventories we use the old fashion plumb bob on a

Mark W. Blunier
Any opinions expressed in this message are not necessarily those of the
Hardy Instruments makes a load cell that can be calibrated without test weights. It has their C2 calibration technology. www.hardyinst.com.
They even have a module that plugs directly into an AllenBradley Slick500 PLC that will monitor up to eight load cells. It is very easy to install
and integrate into an Allen Bradly system. ( Believe it or not ).
In my opinion the ultrasonic is the best solution. As mentioned previously, Milltronics manufactures good quality instruments for such applications as this. Any good brand of "pinger" will be able to cope with dust and angle of repose of the material. (note: different materials can have different angles of repose). The ultrasonic will give a reading of level regardless of density changes in the corn. Any change in density (e.g. from moisture changes) will adversly affect weight sensors. If a load cell system is to be used, preparation and installation is critical. I recommend using three cells 120 degrees apart near the perimeter of the silo. Using three as opposed to four or more ensures the load is evenly spread across all cells. Adequate concrete support should exist for the cells. If this is a new construction I wmight consider load cells, but if the silo is existing I would try an untrasonic first.

Johan Bengtsson

For calibration I was actually thinking of something where it was possible to remove the load cell for off-site calibration (without
the silo falling of course) by applying some kind of replacement support where the load cell was. Buf it that isn't necesary there is no need to implement it. (A question only the original poster may be able answer...)

/Johan Bengtsson

P&L, the Academy of Automation
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Robert Phillips

Just my 2 cents:
We use Drexelbrook RF level sensors for detecting high and low levels in lime (rock) silos. Really suprising that they work with rock but much
better reliability than the VERY old style Bindicators that used something like clock motor to turn paddle that tripped a limit switch when stopped by hitting the lime.

Robert Phillips
Cypress Water Purification
Wichita Falls, Tx

Stan Jackson

We use Milltronics ultrasonic level transmitters for 9- 30,000 cubic ft silos, about 65 ft tall. These have been in operation for 9 years. The
problems we have seen have been minor, but I would consider them if you decide to go this route. The angle of repose will occasionally cause a loss of echo, i.e. the unit stops measuring. You can program these units to fail
high, low, or to hold the last reading. Normally, the problem occurs only when unloading and a wall, or bridge of material briefly appears. (We're measuring fertilizer, but I assume corn will act similarly in a bin.) If your silo has a cone shaped outlet, keep in mind the ultrasonic may have some trouble reading the level when it's near empty, or deep in the cone. I definitely recommend you send a drawing of the silo to the vendor for advise as to transducer placement and sizing. Don't forget to get the aiming kit
that is an option on these. You may also want to consider Endress & Hauser's Level-flex. Essentially it's a steel cable with a weight at the end. Tell them how long you want it to be
and drop it into your silo. We're testing two of these in some applications in which ultrasonics have not performed well due to high dust levels and steep angles. They've been installed for about 4 months so I can't vouch for the long term, but we're very happy with them so far.
If you are going to look at Endress+Hauser's Level-flex, you might also want to look at similar devices made by Drexelbrook, Princo, Bindicator and several others.

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
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Leon van Rensburg

Can you help me with a internet site were i can find the milltronic devices and their specifications, costs. The measuring of grain in a silo is a common problem in the industry. We actually think that without heavy equipment a normal geometry calculation can be use to calculate the volume of the grain. The only problem is to get a formula for the bottom cones in the silo's.