Gravimetric metering device and control method thereof

A method for controlling a gravimetric metering device (1) which is provided to add an additive material to a polymer material, the gravimetric metering device comprising:

• a hopper (3) configured to contain the additive material,
• a supply member (5) which is provided downstream of the hopper (3) in order to receive the additive material which is discharged from the hopper and to transport it towards a discharge opening (9) which is connected to the polymer material,
• a first weighing element (16) and a second weighing element (17) which are associated at least with the hopper (3), and
• a control unit (11) which is associated with the supply member (5) and the first and second weighing elements (16, 17),
• wherein the method comprises:
• detecting, by means of the first weighing element (16), the weight of at least the hopper (3),
• determining, by means of the control unit (11), the flow rate of additive material which is discharged from the gravimetric metering device (1) within a predefined time period from the weight measurements detected only by the first weighing element (16),
• regulating the supply member (5) in accordance with the flow rate of additive material which is discharged from the gravimetric metering device (1) within the predefined time period,
• detecting at the same time the weight of at least the hopper (3) by means of the first weighing element (16) and by means of the second weighing element (17) at the start and at the end of a cycle for charging the hopper (3) with the additive material,
• comparing the weight values detected by the first and second weighing elements (16, 17) and,
• if the weight values differ from each other by a quantity or a fraction greater than a predefined threshold, emitting an alarm signal.