The main condition for suvesseful application (utilization) of the automatic control systems of the production processes in ore dressing plants is continuous control of the production processes parameters and their reliable regulation under the working conditions in accordance with the selected algorithms of control.
The control of production process to be effective if is necessary to have three types of controlled parameters, which characterize the quality and quantity of ore materials being treated respectively and also production situations, condition of production facilities.
Quality indexes of the ground material on different stages of production process can be estimated by its density. The task of control is however complicated by the fact that ground material is contained in the liquid medium which contains also gaseous phase (gaseous vials).
At the Krivoy Rog Technical University one has worked out a combined method for control of the solid phase in gas containing suspensions, based on measuring the Lamb waves propagated on the surface, being in contact with investigated medium and gamma radiation which passed through the latter.
If the plate on which the Lamb wave is propagating boarders on liquid and sound velocity in the liquid 
is less than the velocity C of Lamb wave in the plate, so the Lamb wave will attenuate, emitting the energy into liquid. Attenuation coefficient for Lamb waves on the unit of length is determined by formula
| (1) |
where 
is density of liquid, boardering on the plate surface; r
is density of plate material
| (2) |
where ks,a is wave number for symmetrical and antysymmetrical Lamb waves;
kl and kt are wave numbers of the longitudinal and transverse waves of the plate material.
It should be noted the Lamb waves attenuation coefficient k2 increases monotously by the growth of 
and this means that k2 can be expressed as
| (3) |
where Cv is the value, which, practically does not depend on liquid density.
Fig. 1 shows the dependence of attenuation coefficient per the Lamb waves upon the medium
parameters 
Poisson's ratio of plate material is 0,3.
Fig. 2. shows the dependence of relative measurements value of Lamb waves velocity on the medium parameters at the same conditions.
Fig 1: Dependence of attenuation coefficient per Lamb wave length
on the medium parameters
| 
Fig 2: Dependence of relative measurement value of Lamb waves velocity
on the medium parameters
|
As the pulp gaseous phase does not practically influence on its density, the gaseous vials will not exert influence on the Lamb waves attenuation. In this case the pulp density
will be determined by volumetric portion of the solid material in pulp W, by their mean density rT and by the water density r B
| (4) |
That is why the attenuation coefficient k2 can be represented as
| (5) |
So, the Lamb waves intensity at a distance l from waves source can be determined according to formula
| (6) |
Of me assume W to be equal 0 (zero) in formula (6), we shall have an expression, which will determine the intensity of the Lamb waves during the contact of the plate with cream water.
| (7) |
Attenuation coefficient of pulp's gamma-radiation can be represented by the following expression
| (8) |
where m B
and m T
ore mass attenuation coefficients of water and pulp's solid component;
r B and r T
- the density of water and pulp's solid particles;
W - volumetric portion of the solid particles in pulp.
If the source of radiation (emission) is collimated, the detector will basically register the unscattered radiation, the intensity of which can be expressed as
| (9) |
Where Io is the intensity of gamma-radiation when there is no pulp (liquid) in measuring module (in sludge line).
When there is clear water in measuring module, then the intensity of gamma-radiation will be determined by formula
| (10) |
As one can see in formulas, the intensity of radiation can be represented as
| (11) |
The current value of gamma-radiation detector is proportional to the radiation (emission) intensity so the value of signal S at the logarithmic amplifier yield will be proportional to lnI. In formula (11) one can see the difference between signals S and S*
(S*
is a signal along clear water) will be determined by formula
| (12) |
where A is a coefficient of proportionality.
As it was show before such a signals difference along the Lamb wavesvides a value which is also proportional to the volumetric portion of W i.e.
| (13) |
Let us find out SL and Sg
signals ration
| (14) |
As can see in formula (14) the signal, obtained in such a way will depend only on the average density of the solid material r T
.
The laboratory and production tests of the technical facilities putting into operation the worked out control method for the density of solid phase within the gascontaining suspensions have confirmed its high efficiency.
Bibliography
- Victorov I.A. Surface sound waves in solids - M. Nauka, 1981. -287 p.
- Pat. 5078011 USA, G 01
9/24. Method of monitoring parameters of solid phase of sudpension and devise therefor/Morkun V.S., Potapov V.N. (USSR); Krivorozsky gornorudny institut. - 449856.
