Elastic gauges

In many cases a Fortin-type barometer (Fig. M-13) is suitable. In this case the merexuy in the well is exposed to the atmosphere with the other end evacuated and sealed. All barometer readings shotdd be corrected for temperature, local gravity, and capiUary effect. Atmospheric pressure can also be measured by an aneroid barometer, which is a special type of elastic gauge. It is sometimes used in place of a manometer-type barometer because of the ease of transportation. 

Principle, design, and operation testers. Deadweight testers are the most common instrument for calibrating elastic gauges with pressimes in the range of 15 to about 10,000 Ih/in or higher. 

In elastic gauges, an elastic member is caused to stretch or move by a given pressure. The movement is amplified through a linkage and usually is employed to rotate a pointer indicating the pressure reading in relation to atmospheric pressure. 

All elastic gauges must be calibrated continually to ensure accuracy. Accuracy to 0.5 percent or better of full scale can be obtained. 

Piezoresistive Sensors. The distinction between strain-gauge sensors and pie2oresistive (integrated-circuit) sensors is minor. Both function by measuring the strain on an elastic element as it is subjected to pressure. A pie2oresistive transducer is a variation of the strain gauge that uses bonded... 

Several other elastic materials may be made by copolymerising one of the above monomers with lesser amounts of one or more monomers. Notable amongst these are SBR, a copolymer of butadiene and styrene, and nitrile rubber (NBR), a copolymer of butadiene and acrylonitrile. The natural rubber molecule is structurally a c/i -1,4-polyisoprene so that it is convenient to consider natural rubber in this chapter. Some idea of the relative importance of these materials may be gauged from the data in Table 11.14. 

A published collection of selected reprints concerning piezoelectricity under shock loading and related piezoelectric gauges is available as a convenient source for work in the area of shock-compressed elastic piezoelectrics [78G02]. 

Fig. 2. A schematic variation of the thermal expansion, reduced to the gauge length 1, for the components of the composite (f corresponds to the elastic filler, m to the matrix, i to the mesophase and, c to the composite). The (Al/IJ of the composite is chaneing slope twice, at Tg, and Tgm. The Tgc is found approximately by the intersection of the two external linear branches of the (Al/lc) = f(T) curve...

It is based on equilibrium properties and is directly related to the Gibbs elasticity (17.). In the present context a gauges how strongly the surface tension depends on the surfactant distribution along the bubble interface. Second, captures the kinetics of the adsorption process and is defined by... 

Many control problems can be better solved with a diaphragm controller. The function of the diaphragm controller (see Fig. 3.27) can be easily derived from that of a diaphragm vacuum gauge the blunt end of a tube or pipe is either closed off by means of an elastic rubber diaphragm (for reference pressure > process pressure) or released (for reference pressure < process pressure) so that in the latter case, a connection is established between the process side and the vacuum pump. This elegant and more or less automatic regulation system has excellent control characteristics (see Fig. 3.28). 

Overpressure gauges with elastic measuring element for general use Requirements ... 

Those that are based on the measurement of the distortion of an elastic pressure chamber (mechanical pressure gauges such as Bourdon-tube gauges and diaphragm gauges)... 

Work in groups of four. A tensile specimen of 0.505-in. diameter and 2-in. gauge length is subjected to a load of 10,000 Ibf that causes it to elasticly deform at constant volume to a gauge length of 2.519 in. 

Elastic strain element, e.g. Bourdon tube 2) 1 -15 1 in 103 0.5 for typical gauge Mostly used type of gauge... 

Further devices use strain-gauge transducers as so-called dead-end instruments or sensors mounted on a pipe with internal flow. The principle of this arrangement is the elastic deformation of a metallic cylinder, measured with the strain gauges. Pressures up to approx. 15 kbar can be measured [11]. 

Pressure is measured extensively in the chemical processing industries and a wide variety of pressure measuring methods has been developed. Some of these have already been discussed in Volume 1, Section 6.2.2, viz. the manometer (which is an example of a gravity-balance type of meter), the Bourdon gauge (an example of an elastic transducer) and mention is made of the common first element in most pressure signal transmission systems—the differential pressure (DP) cell (Volume 1, Section 6.2.3). The latter also frequently forms part of a pneumatic transmission system and further discussion of this can be found in Section 6.3.4. 

Electrical output transducers exist in many forms and consist simply of elastic elements coupled with suitable displacement transducers such as capacitance, inductance and reluctance pick-ups, certain types of strain gauge, piezoelectric elements, potentiometers and eddy current probes. A selection of these is described in the following paragraphs. 

Resistance temperature detector (RTD) Venturi Elastic element Chain gauge Mass spectrometry (MS)... 

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