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Electronic Pressure Measurement

Electronic Pressure Measurement
74Pages

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Electronic Pressure Measurement VERLAG MODERNE INDUSTRIE Electronic Pressure Measurement Basics, applications and instrument selection

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verlag moderne industrie Electronic Pressure Measurement Basics, applications and instrument selection Eugen Gaßmann, Anna Gries

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This book was produced with the technical collaboration of WIKA Alexander Wiegand SE & Co. KG. The authors would like to extend their particular thanks for the careful checking of the book’s contents to Dr Franz-Josef Lohmeier. Translation: RKT Übersetzungs- und Dokumentations-GmbH, Schramberg © 2010 All rights reserved with Süddeutscher Verlag onpact GmbH, 81677 Munich www.sv-onpact.de First published in Germany in the series Die Bibliothek der Technik Original title: Elektronische Druckmesstechnik © 2009 by Süddeutscher Verlag onpact GmbH Illustrations: No. 19 Phoenix Testlab GmbH,...

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Contents Introduction Pressure and pressure measurement Sensor technology Pressure measuring instruments Standard applications and requirements Criteria for the instrument selection The company behind this book

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Variety of applications and instruments Instrument selection Electronic pressure measurement contributes to the safe, accurate and energy-saving control of processes. Alongside temperature measurement, it is the most important and most commonly-used technology for monitoring and controlling plants and machinery. Particularly in pneumatics and hydraulics (Fig. 1), measurement and control of the system pressure is the most important prerequisite for safe and economic operation. During the past 20 years, electronic pressure measurement has been introduced in a multitude of applications, and...

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Introduction 5 Fig. 1: Typical application of pressure measurement: pneumatic and hydraulic applications in factory automation knowledge about the physical principles of pressure measurement, the advantages and disadvantages of different sensor technologies in relation to the particular application, and also about the key basics of instrument technology. The selection of the suitable pressure measuring instrument is based, among other things, on such criteria as the pressure range, the pressure or process connection, the electrical connection, the output signal and the measuring accuracy....

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Pressure and pressure measurement In process systems two of the most important process variables to measure are temperature and pressure. The common pressures measured are the hydrostatic pressure of a liquid column and the atmospheric pressure. In general, pressure is defined as follows: if a force per unit area is applied in a direction perpendicular to a surface, then the ratio of the force value F to the surface area A is called pressure p: p= To transmit pressure, incompressible media such as liquids are suitable. To store energy in the form of pressure work, compressible media such as...

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Absolute, gauge and differential pressure 7 Pressure unit 1 bar 1 psi 1 MPa 1 kg/cm2 Conversion 1000 mbar 105 Pa 6895 Pa 68.95 mbar 10 bar 106 Pa 0.0981 MPa 0.981 bar Megapascal (MPa) and “kilogram(-force) per square centimetre” (kg/cm2). Table 1 displays the correlation of these pressure units. Table 1: International pressure units Absolute, gauge and differential pressure Absolute, gauge and differential pressure are three measurement parameters that differ in their reference points, i.e. in the corresponding zero point of the pressure scale. The zero point of absolute pressure is always...

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8 Pressure and pressure measurement For some applications, the difference between two variable system pressures is the actual measurement value. This is known as the measurement of differential pressure. A practical example of this is differential pressure monitoring upstream and downstream of a filter element (see Critical value monitoring, p. 39 f.). Principles of electronic pressure measurement From pressure to electrical signal For electronic pressure measurement a sensor is required to detect the pressure and/or its change, and to convert it accurately and repeatably into an electrical...

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Principles of electronic pressure measurement 9 Fig. 3: Change of the dimensions of a cylindrical conductor by elongation metallic conductor is a (temperature-dependent) constant for a particular material and, therefore, independent of the geometry, the electrical resistance increases as a result of the elongation. In the case of compression, the opposite applies. The principle of resistive pressure measurement is realised using a main body which exhibits a controlled deflection under pressure. This main body frequently has a (thin) area referred to as the diaphragm, which is weakened...

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10 Pressure and pressure measurement … with metallic strain gauges Silicon diaphragm with integrated strain gauges Encapsulation of the sensor element Usually four strain gauges are applied to a diaphragm. Some of them are located on elongated and others on compressed areas of the diaphragm. If the diaphragm deflects under the action of a pressure, the strain gauges are deflected correspondingly (Fig. 4). The electrical resistance increases or decreases proportionally to the deflection (elongation or compression). To accurately measure the resistance change, the strain gauges are wired to a...

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Principles of electronic pressure measurement 11 pressure must then be transmitted indirectly to the semiconductor sensor element, e.g. using a metallic diaphragm and oil as a transmission medium. Due to the magnitude of the piezo-resistive effect, piezo-resistive sensors can also be used in very low pressure ranges. However, due to strong temperature dependency and manufacturing process-related variation, individual temperature compensation of every single sensor is required. Capacitive pressure measurement The principle of capacitive pressure measurement is based on the measurement of the...

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12 Pressure and pressure measurement Fig. 5: Capacitive measuring principle Fixed plate Moving plate sure values, even down in the one-digit millibar range. The fact that the moving diaphragm can be deflected until it reaches the fixed plate of the capacitor ensures a high overload safety for these pressure sensors. Practical restrictions on these sensors arise from the diaphragm material and its characteristics, and also from the required joining and sealing techniques. Piezo-crystalline diaphragm Piezo-electric pressure measurement The principle of piezo-electric pressure measurement is...

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Electronic Pressure Measurement 74Pages

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Electronic Pressure Measurement
74Pages