Check weigher
A checkweigher or checkweigher is a scale that is used to monitor the manufacture / production of goods according to weight criteria. They can be divided into static and dynamic checkweigher. In the production process usually automatic dynamic control scales are used because of the automation, the test object measured in the flow.
Automatic dynamic checkweigher
Automatic control scales within the definition of the calibration law in Germany since about 1965 in use. Already at that time reached, also known as " checkweigher " automatic belt scales respectable performance in terms of clock speed and accuracy. However, the handling was still very cumbersome, since neither modern digital technology nor rapid, high-resolution load cells were available with satisfactory linearity. In the course of technical progress Checkweighers are now controlled by fast processor systems; as load cells, several model principles to choose from.
The main application areas of control scales are:
A scale is (point 2) used for economic reasons, to control the production process and to optimize. Feedback control systems and trend report back to bottling systems to intervene regulating. Control and improvement of use of goods are in the foreground. The tendency of a control checkweigher constantly detects the product weights and calculates an average cyclically. This is compared to the target value and the basis of the deviation, a correction signal for Dosier-/Schneidevorrichtung is given, which is proportional to the size of the deviation. This product weight is medium and long term optimized such that a quasi- coincidence between the actual value and setpoint follows. For quality control, the recording and documentation of the weights of importance.
For legal reasons (point 3) that a manufacturer of finished packaging ensure uniform with nominal weight that the products put into circulation products do not fall below certain values on average ( TU1 ) or absolute ( TU2 ). The scales used here must be calibrated to ensure a sound documentation of products sold.
Construction
Typical checkweigher consists of a system of aligned conveyor belts, one of - the weighing belt - is constructed in a fast, high-resolution measurement cell.
Outline of the conveyor belts
Very important for accurate measurements is to separate the products fed before weighing perfect, so during a measurement only one product is always positioned fully on the weighing belt is. This is not due to the characteristics of the upstream units possible, a checkweigher may also be provided with, if necessary, a plurality of strips prior to the actual acceleration of the weighing belt.
A) feed belt / decrease from previous tape machine b ) Optional Acceleration belt to separate to products c ) weighing belt d) make band / with sorting out for " bad" - classified products
Load cells
The load cells used today - also known as cells - are full -range scales in the rule. The main types used in control scales are:
- Force -compensated measuring cell
- Load cell according to the principle of the vibrating string with frequency measurement