Design of an Acoustic Transmitter for Temperature-Pressure Dual Sensing in Injection Molding

This paper presents a new sensing method for the simultaneous measurement of temperature and pressure within an injection mold cavity for molding process monitoring. A temperature-dependent oscillator (TSO) was designed to convert changes in the polymer melt temperature into carrier frequency shifts of the TSO by means of a temperature-sensitive capacitor. The frequency shifts are then utilized to modulate ultrasonic pulses generated by an ultrasonic transmitter. The ultrasonic transmitter is powered by energy extracted from the melt pressure by means of a piezoceramic stack. The transmitter and the TSO were represented by an equivalent circuit, and its Mason´s model was analyzed to assist in the parametric design and function simulation of the transmitter. Results of simulation were experimentally verified and a good agreement was found.