In Mold Pressure Sensing Architecture for Multi Cavity Tooling Setup
In-cavity piezoelectric pressure sensing setups in multi-cavity tools decouple fill control from hydraulic drift to minimize scrap and verify part density.
Thermal Baseline Drift
Meaning
Unintended changes in sensor output occur when the ambient or process temperature alters the reference point of a measurement device. In continuous extrusion and moulding lines, thermal baseline drift affects pressure transducers that reside close to the hot barrel or die. This drift shifts the recorded pressure curve upward or downward even when no physical pressure change has occurred.
It is bounded by the thermal compensation range of the sensor.
Physical Origin
Sensor materials expand and contract when heated, causing subtle changes in the resistance or capacitance of the measurement circuit. During a long production run, thermal baseline drift happens as heat from the polymer melt conducts up the shaft of the transducer. This temperature increase affects the internal strain gauges or piezo-elements.
The resulting offset can misrepresent the actual pressure inside the melt stream. Without an automated software routine to recalibrate the sensor between shots, this progressive change leads to a systematic error that distorts the recorded injection pressure profile.
Process Error
Erroneous data from drifting sensors leads to incorrect adjustments in the process control system. When thermal baseline drift occurs, the controller may increase the screw speed to compensate for an apparent drop in pressure, leading to over-pressurization of the tool. This error can cause flash or part sticking in injection moulding.
Accurate diagnostics require comparing the sensor output to a cold-start baseline.
Calibration Adjustment
Modern control systems implement automated zeroing routines to correct for gradual temperature shifts. The software resets the baseline value during the idle time between moulding cycles when the cavity is empty. This adjustment ensures that each cycle begins with a calibrated sensor reading.
Consistent zeroing prevents accumulated errors from affecting the part quality over a multi-day production run.