Method of and apparatus for weighing doses of powder

Method of dosing a powder by weight, employing a balance 12 provided with a weighing receptacle 11 and with means 13 for continuously measuring the effective weight of the effective contents of the receptacle 11, and means 4, 5 for positively feeding powder to be dosed toward the weighing receptacle 1, consisting of means which during a dosing cycle energizes feeding means 4, 5 at an initial instant t.sub.0 at which the receptacle 11 is theoretically empty to a final instant t.sub.2 in which the receptacle 11 has received from the feeding means 4, 5 since the initial instant, a weight of powder of a predetermined value P.sub.2 less than a predetermined final value to be obtained P.sub.3 of a quantity corresponding (P.sub.3 minus P.sub.2) to an error of powder loss caused by the feeding means 4, 5 to interrupt at such final instant t.sub.2 the functioning of the powder feeding means 4, 5 and to permit thereafter residual powder flow into the receptacle 11 corresponding to the effective amount of the error through powder loss, characterized in that the final instant t.sub.2 has been predetermined with reference to the initial instant t.sub.0 as well as an ideal evolution I of the weight of powder received by the receptacle 11 as a function of time from the initial instant t.sub.0 to the final instant t.sub.2, and that each instant of the operation of the feeding means 4, 5 the effective weight of the powder received by the receptacle 11 since the initial instant t.sub.0 is compared with a theoretical weight which conforms to the ideal evolution I and one continuously controls the operation as a function of the resultant of such comparison, in order to increase the rate of flow of powder if the effective weight thereof is less than the theoretical weight at the instant considered or to reduce the rate of feeding of the powder if the effective weight thereof is greater than the theoretical weight of the powder at the instant considered, and thus to adapt the evolution II of the effective weight of powder received by the receptacle 11, when the feeding means 4, 5 are functioning, to achieve an ideal evolution I of the feeding of the powder, predetermining an upper admissible limit and a lower admissible limit around the said predetermined final value P.sub.3 and in that, at the expiration of a predetermined delay sufficient for the flowing into the receptacle 11, after the final instant t.sub.2, of the residual powder corresponding to the error of powder less during its transmission, one compares the effective weight of powder received by the receptacle 11 to said limits, in order to define a good weight or a bad weight depending upon whether the effective weight is located between said upper and lower limits or outside said limits.