Piezoelectric Cavity Pressure Sensor Setup in Micro Injection Moulding
Direct piezoelectric cavity pressure sensing in micro injection moulding requires sub-micron bore tolerances, rigid preloading, and active thermal drift compensation.
Pyroelectric Interference
Meaning
Spurious electrical charge generated by a piezoelectric crystal in response to temperature changes rather than mechanical force can corrupt pressure readings in injection moulding. This pyroelectric interference occurs when the hot melt front contacts the sensor surface during the injection phase. The resulting signal error can lead to incorrect process monitoring and premature switchover.
Thermal Response
Piezoelectric crystals are inherently sensitive to both temperature and force. When the molten polymer touches the sensor face, a rapid temperature gradient develops. This thermal shock creates a voltage that is called pyroelectric interference.
Process Distortions
The unwanted charge can make the cavity pressure appear higher than it is, triggering a premature transition from fill to pack. If the controller switches over too early, the part will not be filled completely, leading to short shots or surface defects. In cases where the temperature drop is rapid, the sensor can also show a negative pressure reading at the end of the cycle.
Mitigation Strategy
Ceramic insulation or protective coatings are applied to the sensor face to delay the thermal wave. This shielding slows the temperature rise in the crystal, allowing the pressure measurement to finish before the thermal gradient develops. Modern signal amplifiers can also use digital filtering to subtract the thermal component from the combined signal, restoring the true cavity pressure profile.