Meaning
Electrical charge generated per unit of applied force or pressure by a piezoelectric sensor during moulding is defined by this characteristic coefficient. A precise charge sensitivity ensures that the pressure inside the mould cavity is translated into an accurate electronic curve. When this coefficient drifts or degrades due to thermal exposure, the controller receives incorrect pressure readings that can lead to short shots or flashing.
This variable is a function of the sensor’s design and crystal structure, not the material being moulded.
Sensor Output
Piezoelectric elements within the sensor body release minute electrical charges when compressed by the polymer melt. The charge sensitivity of these instruments is measured in picocoulombs per bar of pressure. This output travels through highly insulated cables to prevent signal loss before amplification.
Signal Calibration
Regular calibration must be conducted to account for the gradual loss of responsiveness in harsh moulding environments. The factory charge sensitivity value tends to drift over millions of cycles due to thermal stress and residual pressure loads. Technical operators enter the updated coefficient into the amplifier to restore the accuracy of the process monitoring system.
Failure to calibrate the system results in a mismatch between the displayed pressure and the actual pressure inside the steel cavity.
Process Integration
Automated injection systems use the sensor signal to trigger the transition from the filling stage to the holding stage. If the charge sensitivity has degraded, the system may delay this switchover, leading to overpacking and tool damage. In contrast, an over-sensitive signal can trigger premature switchover, which yields incomplete or weak parts.
Maintaining this value is especially important when using recycled resins, which exhibit wider viscosity variations than virgin materials and require precise pressure-based control to prevent defects.
