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　　　A Silicon piezoresistive pressure sensor for high pressure measurement utilizing a combination of three-axis stress components has been developed. The piezoresistive pressure sensor can be used for measurement of internal pressure in a injection molding machine. The pressure sensor was composed of a force sensor, a stainless steel (SUS630) housing with a diaphragm of 10 mm-diameter in which the force sensor was assembled, a fix screw, a stainless steel (SUS630) case and a resin cap. Pressure is transmitted into force which is applied to four piezoresistors on a silicon sensor chip through a force transmission rod of glass (SW-3). Stresses due to applied pressure in piezoresistors depend on the diameter, height and Young's modulus of the rod, and the diaphragm thickness of the sensor chip. In order to obtain large resistance changes in piezoresistors, the optimum combination of three-axis stress components was investigated by changing of these parameters. An output of the prototyped pressure sensor was more than 50 mV / 5 V at 150 MPa and a sensitivity temperature characteristic was 0.11 % / centigrade in the range from room temperature to 150 centigrade.

Fig.1　Structures of the pressure sensor and the force sensor unit.

Fig.2　Components of the high pressure sensor.

Fig.3　　Output characteristics of the high
　pressure sensor under elevated temperature.

Fig.4　Output change ratios of the high
　　pressure sensor under elevated temperature.