Electric pressure sensors

Many of the variations developed to make pressure sensors and accelerometers for a wide variety of appHcations have been reviewed (5). These sensors can be made in very large batches using photoHthographic techniques that keep unit manufacturing costs low and ensure part-to-part uniformity. A pressure differential across these thin diaphragms causes mechanical deformation that can be monitored in several ways piezoresistors implanted on the diaphragm are one way changes in electrical capacitance are another. 

The component failure rate data used as input to the fault tree model came from four basic sources plant records from Peach Bottom (a plant of similar design to Limerick), actual nuclear plant operating experience data as reported in LERs (to produce demand failure rates evaluated for pumps, diesels, and valves), General Electric BWR operating experience data on a wide variety of components (e.g., safety relief SRV valves, level sensors containment pressure sensors), and WASH-1400 assessed median values. 

Fig. 5.59 shows a section through a Piezo-resistive silicon pressure sensor. The ambient pressure is applied from above, while the pressure being measured is applied from below. A silicon membrane that deforms under the pressure is applied to a silicon carrier structure. Piezo-resistive structures are fitted in the membrane, which then change their resistance accordingly when the membrane deforms. A bridge circuit generates an electrical output signal which is proportional to the difference in pressure. 

Fig. 5.61 shows a section through a capacitive pressure sensor. It consists of a metallic housing that is divided into two chambers by the electrically conductive... 

A sensor is a kind of translator. It receives specific information about the system under investigation and transmits this information in the form of an electrical signal. Sensors are specific to a given property of the system under investigation. Some sensors are sensitive to temperature, others are sensitive to light, still others to pH, pressure, etc. 

All mechanical and electrical components should be examined and verified that they are functioning properly. These components include the solenoid valves for water cooling systems, cooling water pumps, cooling fans, electrical heaters, thermocouples and other temperature sensors, pressure sensors, and gear pump operations. 

Principal uses for this material are found in the electrical/electronics industries automotive parts, such as alternator armatures and pressure sensors optical uses, such as safety goggles and garden vehicles, such as mower decks and shrouds, tractor hoods, grills, and fenders. 

It is also interesting to briefly consider online measurements of variables different from temperature [5], Since pressure is defined as the normal force per unit area exerted by a fluid on a surface, the relevant measurements are usually based on the effects deriving from deformation of a proper device. The most common pressure sensors are piezoresistive sensors or strain gages, which exploit the change in electric resistance of a stressed material, and the capacitive sensors, which exploit the deformation of an element of a capacitor. Both these sensors can guarantee an accuracy better than 0.1 percent of the full scale, even if strain gages are temperature sensitive. 

Presently a commercially available two stage vacuum system comprising a membrane (Pfeiffer MVP 006-4) and a turbo pump (Pfeiffer HiPace 10) in combination with a pressure sensor (Leybold Vacuum Ionivac ITR 90) establish a pressure of about 0.1 Pa in the system. Three electric valves are used to control the gas flow into the capillary system and for the bypasses. The use of macro devices simplifies the handling of the experimental setup and also the electronic control. Pressure drops for plasma and sample gases are accomplished by an appropriate combination of capillaries with different diameters and lengths as described in Sect. 4. 

In recent years, electrical pressure transducers based on the use of strain gauges have been developed for use over ranges varying from 0- 1 PSIG to 0- 10,000 PSIG. The sensor is... 

The pressure losses can be measured by means of the pressure sensors. The circulating fluid is water and it can be heated by four electric cartridges inserted in the two blocks. The heat transfer coefficie nt is deduced from a global heat balance which takes thermal losses into account. 

The aim is to eliminate entrance effects as much as possible and any influence on the flow of the pressure tap holes into the channels. This was achieved by integrating on the same silicon chip the microchannel, the pressure taps and the pressure sensors. The fabrication process and the operating mode are described in [28]. The pressure sensors are constituted cf a membrane which is deformed under the fluid pressure and on which is deposited a thin film strain gauge. This strain gauge forms a Wheatstone bridge whose the membrane deformation modifies the electrical resistances. 

Figure 3 shows the test section and instrumentation. Ten wall temperatures on the tube external surface were measured with 0.5 mm diameter calibrated type E thermocouples electrically insulated from the aluminium. Fluid inlet and outlet temperatures were measured with 1 mm diameter calibrated type K thermocouples. Cah-bration was carried out with a Rosemount 162-CE platinum thermometer. Due to the high thermal conduchvity of the aluminium and the low thickness of the tube walls the measured temperature is very close to the wall temperature in contact with the fluid (the difference less than 0.01 K). The inlet fluid pressure was measured with a calibrated Rosemount type 11 absolute pressure sensor. Two calibrated differential pressure sensors measured the pressure loss through the test section. A Rosemount Micro-motion coriolis flowmeter was used to... 

M. Esashi, Y. Matsumoto, S. Shoji Absolute pressure sensors by air-tight electrical feedthrough structure. Sensors and Actuators A21—A23 (1990), pp. 1048-1052. 

Fiber optic intravascular pressure sensors can be made in sizes comparable to piezoresistive ones, but at a lower cost. The fiber optic device determines the diaphragm displacement optically by measuring the varying reflection of light from the back of the deflecting diaphragm. These optical devices are inherently safer electrically, but lack a convenient way to measure relative pressure without an additional lumen either atmospherically vented or connected to a second pressure sensor. 

The development of flexible pressure sensor films was an important step in endowing robots with skin sensitivity, but e-skins are expected to add at least two more functionalities thermal sensing and conformability. Without conformability, e-skins cannot be applied to three-dimensional surfaces. Stretchable e-skins for humans are commercially available, but they do not possess electric functionality. Indeed, various stretchable materials, like rubber, are used in daily activities, but they have poor... 

In this section, we describe a solution that employs a net-shaped structure to make flexible electronic film devices conformable to three-dimensional surfaces [18]. Although the base films we presently use are of polyimide and poly(ethylenenaph-thalate) (PEN) — materials that are stiff and not inherently stretchable in a rubberlike sense — our solution includes struts of network structures that twist with the application of tension, as can be seen in Figure 6.3.7. Due to this three-dimensional strut deformation, the whole network structure functions electrically with a unidirectional extension of 25%. We have implemented the pressure sensor network on the surface of an egg and have obtained pressure images in this configuration. 

In this section, we describe a manufacturing process for the pressure sensor network. As shown in Figure 6.3.8(a), the sensor cells are positioned at the center of intersection areas and are connected to each other by struts with electrical wirings. The magnified image of a transistor is shown in Figure 6.3.8(b). 

In this section, the electrical performance of the pressure sensor network is described. All electric measurements were performed in an ambient environment with a semiconductor parameter analyzer, unless otherwise specified. With the application of... 

In the present design, the thermal sensor network contains its own organic transistor active matrix for data readout. This arrangement provides for a self-contained thermal sensor when combined with a pressure sensor, yielding two electrically independent networks. The design of the active matrices is exactly the same for both networks. 

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