High-pressure sensors

Post-Oil Energy Technology After the Age of Fossil Puels 

In the renewable energy processes, particularly in the GH2 storage and transportation applications, accurate measurement of high pressures is required. The term high pressure is relative, but for the purposes of this discussion, pressures exceeding 1,000 bar (15,000 psig) are considered to be high. 

The operating principle of strain gauges is more than 100 years old, and it was discovered when Lord Kelvin reported that metallic conductors sub- 

For temperature compensation, the most frequently employed method is the use of dummy elements. The dummy gauge is mounted on the same surfaces as the active element. It is exposed to the same temperature but is not subject to the forces applied. If such a dummy is connected in a Wheatstone bridge arm adjacent to the active element, it will automatically compensate for temperature effects. 

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Assemble the components into the process system and apply FMEA techniques to determine if protection devices on some components provide redundant protection to other components. For example, if there are two separators in series, and they are both designed for the same pressure, the devices protecting one from overpressure will also protect the other. Therefore, there may be no need for two sets of high pressure sensors. 

The application of this procedure is best seen by performing an FMEA on a simple two-phase separator. Table 14-3 lists those process upsets that can be sensed before an undesirable event leading to a source of condition occurs. For overpressure, primary protection is provided by a high pressure sensor that shuts in the inlet (PSH). If this device fails, secondary protection is provided by a relief valve (PSV). 

High Pressure Sensor Pressure Safety High ... 

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. 4.1.12 Thin-film metal structures on the steel membrane of Bosch s high-pressure sensor and the equivalent circuit of a Wheatstone bridge [27]...

Here we show an example of applying the EFS method to a non-silicon-based pressure sensor to operate at high pressure ranges. The membrane of many high-pressure sensors (Bosch, WIKA) is manufactured of steel, with thin-film metal resistors as a measurement signal pickup (Fig. 4.1.12). 

Fig. 4.1.13 Part of the EFS matrix for Bosch s high-pressure sensor, showing the influence of selected model parameters on 3 functional parameters...

Figure 4.1.16 shows the same comparison for the offset of Bosch s high-pressure sensor. 

J. Muchow, A. Kretschmann, R. Henn, K. Skrobanek, S. Finkbeiner, H.-R. Krauss, Influence of process variation on the functionality of a high pressure sensor, Design, Test, Integration and Packaging of MEMS/MOEMS, DTIP 2002, SPIE Proc 4755, Bellingham WA, USA, 2002, 143-148. 

Polysilicon and NiCr are currently used for high volume production of high pressure sensors. Because the origin of the change in resistance as a function of the applied strain is different for the two materials, we will analyze the physical contributions to the gauge factor and then discuss these materials in more detail. The Wheatstone bridge, which is commonly used to detect small changes in resistance, is also discussed. 

Three layers have to be patterned to fabricate strain gauges the sensing layer, the contact layer, and the passivation layer. Usually, the highest precision is required when patterning the sensing layer. Minimum line widths are about 30 pm. Examples of layouts for high-pressure sensor elements are shown in Fig. 5.4.11. 

Fig. 5.4.11 View of thin film system in high-pressure sensor elements of Nagano Keiki Co. (left) and Robert Bosch GmbH (right)...

Thin film technology on steel is well suited for high precision sensors in automotive applications. Well established applications include high pressure sensors in the range of 140 to 200 MPa. For these applications, a manufacturing volume of several million sensors per year has been reached. 

This can further be enhanced by the so-called lock-in technique, in which modulated signals are used, which after demodulation separate the desired signal from the noise. Both techniques are described here by examples one is a monolithic pressure sensor with moderate piezoresistive bridge signals and the other is a signal evaluation circuit for a high-pressure sensor with very small sensor signal levels. 

Fig. 6.2.14 shows the chip photo of the realized signal processing ASIC for high-pressure sensors. The signal conditioning operates in the above described manner. The parameters of the sensor are as follows ... 

This system improves driving safety by preventing lateral instability of the vehicle. Besides sensors for wheel speed, steering-wheel movement, and yaw rate, a high-pressure sensor is needed to detect the brake pressure. 

Tab. 7.4.1 High-pressure sensors in automotive applications and typical pressure sensor ranges...

Fig. 7.4.2 Components of gasoline direct-injection system with high-pressure sensor...

Typical requirements for automotive high-pressure sensors can be defined from the environmental conditions in the engine compartment and the needs of the applications, as follows. 

High-pressure sensors differ mainly in the measuring principle used and the type of internal connection. Most sensor designs use a steel diaphragm to separate the pressure fluid from the sensor signal and environment. 

To meet the automotive requirements the design of the high-pressure sensor plays a decisive role with respect to the measurement task. Fig. 7.4.7 shows a cross section of a pressure sensor for gasoline direct injection systems. 

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.

To reach future requirements for brake and direct injection systems requires high-pressure sensors that have the following properties. 

Otake, S., Ondada, M., Nagase, K., Automotive High Pressure Sensor, SAE Technical Paper 980271. 

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