If you have a classic weighbelt feeder with a flood-fed inlet, the material profile will be consistent.

The loadcell measures belt loading, when divided by profile cross section will equal bulk density. This is an easy PLC calculation to accomplish.

Regards, Delmar Schmidt

Melfi Technologies Houston

www.melfitechnologies.com ■

Hi Sanja,

You can measure the density in small samples, but haven't heard of anything which can measure online. If you hear anything, please let us know as well. You can also increase the frequency of sampling to minimum possible, depending on the product you choose.

Thanks,

Vik ■

Sanja,

Bulk density can be measured continuously in-line using a device of the type outlined in the attached file. A device of this type has been in industrial service for about 10 years, measuring the BD of a detergent product; (the device actually replaced a weigh belt method which was not satisfactory).

Clive Davies

Massey University

Attachments

bulk density_general article (PDF)

■

Sanja,

To the best of my knowledge there is no commercial supplier of items of the type I described in my last post.

For the case I referred to, I designed the item and arranged its construction.

Contact me for further information if you wish.

Clive Davies

Massey University ■

Of the methods suggested; one is for solid items, one even ignores the target i.e. if density changes why should the belt stay flooded just to maintain a constant cross section i.e. who told the weighfeeder the material had got denser? The other one doesn't give a full cross cut measurement so it won't qualify for accounting purposes. It also needs to screen out the influences of impacts from denser materials.

In other words there isn't yet a method explained to satisfactorily quantify bulk density on line or in line. ■

I worried about this query as it is inevitable that the density will change on discharge from a belt and depend on how the material is formed. However, I concluded that the user is interested in whether the condition of the material was consistent, rather than what the value of density actually was at the particular location on the belt. The shape of the cross section would only be reasonably stable if the belt was extracting from a hopper as a feeder, in which case a weigh belt could detect a density change if the weight varied significantly, assuming that the cross section and belt speed were unchanging. I would consider this to be more of a consistency indication than giving an actual bulk density value and only be useful for relatively large changes in density. Perhaps an alternative method to detect density change would be an inverted weir section on the belt to give a steady thickness of bed that could be scanned by a gamma ray detector. The basic problem is all cases is to create a known volume or thickness and simultaneously secure a measurement of mass. An impact flowmeter could, in theory, relate to density if a controlled volume of product could be diverted to the recording device.

If the matter was of sufficient interest, one could look at making a scoop device that lowered into the belt stream and lifted out to be weighed, then tipped back onto the belt. Alternatively, a collecting tub with flap base that recorded the time to attain a given weight before opening the flap to release the contents would indicate a change of density from a controlled volume belt feeder. However, these developments seem unlikely to be commercially attractive to undertake for a one off or a potential hot repeat sales item, so would have to be initiated by the interested party. Checking the bulk density of a flow stream that is of uncertain, or varying volume is quite a challange and I do not know of a commercially available device. ■

Hi Sanja;

Berthold Technologies have an inline Nucleonic Bulk Mass Flow Meter.

If you profile the material to a constant cross sectional area; the output can be extrapolated as density.

Their site is

www.berthold.com ■