Stability high-pressure sensors

A further requirement for a pressure sensor is the stability of the host lattice at high pressures and temperatures. This requirement strongly narrows the range of possible candidates for high-pressure sensors. From X-ray diffraction experiments under pressure, it was found that YAG is stable at least up to 69 GPa at room temperature (Liu and Vohra, 1993). This is one of the reasons why doped YAG was chosen by many researchers as a promising host for pressure calibrants. 

Fig. 7.4.8 shows the results of endurance testing of a metal thin-film high-pressure sensor with the design shown in Fig. 7.4.7. Typical deviations from the ideal characteristic can be seen. The sensor has been tested in a gasoline direct injection car for 162000 km. The deviation is shown for pressures up to 140 bar and temperatures between —40 and 140 °C. Hysteresis can be seen for increasing and decreasing pressures at each measuring temperature. The maximum deviation of about 0.3% FSD demonstrates the long-term stability of the sensor package design and the thin-film technology.

By dispersing carbon black into POD-DPE, conductive composites can be obtained. The presence of carbon black enhances the thermal stability. The resistivity decreases continuously with an increase of pressure. Further, the composite shows a t5 ical semiconductor behavior, characterized by an increase of conductivity with temperature. The thermal and electrical properties and pressure sensitivity make this compound a good candidate for the application in manufacture of pressure sensors for high ambient temperatures. 

As a general feature of most osmometers, the membrane is clamped into a stainless steel thermostated chamber (the measuring cell and the pressure measuring system of modem osmometers are built into a high-grade electronically stabilized thermostat) and serves as barrier between the pure solvent and the polymer solution sides of the chamber. The solvent side (bottom) is in juxtaposition with a pressure sensor, e.g., the diaphragm of a capacitance strain gauge or a piezo-chip. The solvent transport is measured across the... 

The stability of ceramic materials at high temperatures has made them useful as furnace liners and has led to interest in ceramic automobile engines, which could endure overheating. Currently, a typical automobile contains about 35 kg of ceramic materials such as spark plugs, pressure and vibration sensors, brake linings, catalytic converters, and thermal and electrical insulation. Some fuel cells make use of a porous solid electrolyte such as zirconia, Zr02, that contains a small amount of calcium oxide. It is an electronic insulator, and so electrons do not flow through it, but oxide ions do. 

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