GB1243546A - Pressure transducer with reduced temperature sensitivity - Google Patents

Abstract

1, 243, 546. Pressure transducers. KISTLER INSTRUMENT CORP. Dec.10, 1968 [Feb.7, 1968], No.58722/68. Heading G1N. A fluid-pressure transducer, 10, comprises a pressure-sensing invar diaphragm, 64, a ceramic heat-shield 74, 76, a Piezo-electric element 42 and temperature compensating plates 44, 46. The transducer is used to measure pressure inside an internal combustion engine where the heat-shield and an invar heat-shroud 80 protect the diaphragm from transient thermal shocks, the gas pressure being transmitted through a narrow annular passage, 78. Long-term temperature compensation is effected by selecting for the plates 44, 46, materials of which the co-efficients of thermal expansion are respectively greater and less than that along the transverse or Y-axis of the quartz crystal wafers, (110, 112, 114, 116) Fig.11, (not shown) of the Piezo-electric element. The crystals are X-cut so as to include two mutually perpendicular stress-sensitive axes, the X-axis being aligned along the longitudinal axis 150 of the transducer while the Y-axis is transverse of it. Compression along the Y-axis produces an electric charge of equal magnitude but opposite polarity to that generated by an equal compression along the X- axis. Initial pre-stressing of the Piezo-electric element is achieved by stretching an invar sleeve 40 and end-piece 50, so as to urge the element to the metal base 12, before spot-welding it at 58, 60, 62. Compensation for acceleration effects is achieved by connecting one of the crystals in seriesopposition to the others.