Compliance with pre-packing regulations
Automatic checkweighers have been in use since around 1965. Many applications of these scales are subject to national legislation on minimum and average weights. Manufacturers selling pre-packaged products with uniform nominal weights to end users must ensure that the products put into circulation are not lower than certain nominal values. Compliance with this rule is ultimately the responsibility of such pre-packaged manufacturers.
In order to comply with pre-packaging regulations, many countries in the world also require regular inspections (called "verification" in Europe) of the measuring equipment (checkweighers) used in these production facilities.
In the European Union, Russia and Japan, in addition to the initial market and regular on-site inspections (certification, recalibration), the laws of these regions also require type certification of these measuring instruments (checkweighers), which proves that national accreditation bodies (such as PTB, NMI, etc.) have proved the measurement accuracy of the instrument on the basis of previous tests. (EU: MID regulation). Type certification is a prerequisite for putting into use under actual production conditions or recalibrating the checkweigher on site.
The product to be weighed can be liquid, powder, or solid component, and these components can have an infinite number of different weight values. However, some products contain a limited number of parts whose individual weight is more or less known. Therefore, these products (theoretically) can only assume a limited number of weight values. In particular, people may only think of one or a few missing components that will make the final packaged product incomplete.
The task of the dynamic checkweigher is to check the integrity of the product and remove incomplete products from the production process with sufficient measurement reliability. Integrity control can be used for individual packaging as well as final packaging for production lines such as cartons.
Another task is pure internal quality control, where deviations in the target weight (too heavy or too light) indicate production errors, such as weight control of castings. From its weight, it can be seen whether there is shrinkage (internal air bubbles), which needs to be eliminated. Controlled parts.
In the applications mentioned above, classification is also used, but only classified as good or bad, and certain weight values are accepted or rejected. However, another application is classification in the sense of category assignment. There are usually several continuous unloaders used to deliver products of different weight levels into different channels or collection containers, and then these channels or collection containers contain only products within the previously defined weight range. For example, collection container No. 1 contains products weighing between 100g and 120g, collection container No. 2 only contains products weighing between 120g and 140g, and so on.
Filling and batching process optimization (trend controller)
Another task of the checkweigher is the active control of the filling process. The so-called checkweigher trend controller, whose task is to influence the filling, segmentation or slicing upstream of the checkweigher through corresponding control signals to achieve the weight value defined as the target weight and keep it as constant as possible.
For this reason, the weighing results are evaluated accordingly. The result of the evaluation is to send a control signal (regulated variable) for adjusting the filling unit. The input control parameters determine the type of evaluation and control characteristics. These must be adapted to the characteristics of the filling unit to be controlled. The parameter "target value" defines the desired target weight to be maintained.