The operating principle of these associative machines is as follows: the bulk product is distributed in small doses, called samples, among the containers that carry out the weighing. These samples are fractions of the desired final weight, so that the weigher can accumulate them to obtain that desired final weight (if one of the samples exceeds the desired final weight, it will not work and must be expelled in a process called "rejection"). .
The size of the samples can be controlled by operating parameters such as intensity or time of vibration of the vibrating channels or advance time of pre-dose tapes or distribution of samples, so that the user of the machine must adapt them to the weight they want to obtain. .
Obtaining the desired weight is achieved by calculating all the possible combinations between the samples available at that moment in the machine and choosing the one that adds the value of the desired weight. The more samples in combination, the greater the possibility of obtaining the exact value of the desired weight.
However, each machine model has a limited number of heads and therefore samples, so a BAND OF DESIRED WEIGHTS is usually specified instead of a single value, to avoid that the machine is blocked if there is no valid combination. . This weight band can be specified by indicating allowable tolerances above and below the desired weight. For example, with a desired weight of 1000 grams, a tolerance above 10 grams and below 5 grams, which is telling the machine to look for a combination of samples that adds up to 1000 grams and if it cannot find it, that you look for the closest to 1000gr between 995 and 1010 gr (if you do not find it in this range either, a series of automatic measures are usually applied to prevent the machine from blocking).
The dosing of samples to the weighing containers can be carried out in different ways, depending mainly on the nature of the product to be processed. Generally vibrating channels will be used, but in special cases it may be necessary to resort to belts (fresh meat products) or volumetric dispensers type glass (some precooked). The arrangement of the in-line or circular containers is also often determined by the product.