Meaning
Resonator equivalent circuit parameters represent the mechanical energy loss of a vibrating piezoelectric sensor. In sensor applications for polymer extrusion and moulding, the motional resistance r1 corresponds to the viscous drag exerted on the crystal surface by the polymer melt. This resistance increases as the surrounding polymer becomes more viscous or starts to solidify in the cavity.
Viscous Interaction
Drag from the polymer melt dampens the oscillations of the piezoelectric crystal, increasing the motional resistance r1 of the circuit. In a low viscosity environment, the crystal oscillates with minimal resistance, keeping the motional resistance low. As polymerization progresses or as the melt cools, the increasing viscosity raises the electrical resistance of the motional branch.
This change provides a direct correlation to the rheological state of the material, allowing the controller to map the viscosity curve of the polymer as it fills and packs the mould.
Melt Diagnostics
Monitoring the changes in this electrical parameter enables real-time tracking of the viscosity. When the motional resistance r1 stabilizes, it indicates that the polymer has completed its phase change and is fully solidified. This measurement is crucial for optimizing the cycle time, as the part can be ejected as soon as the plateau is reached.
Sensor Calibration
Air baseline values must be established before the sensor is exposed to the polymer flow. If the initial motional resistance r1 is not measured in a clean environment, the subsequent increase in resistance cannot be converted into absolute viscosity values. This calibration step ensures that the viscosity measurements remain accurate and comparable across different production runs.
