Lecture Sensors and analytical devices: Pressure measurement - Nguyễn Công Phương

This chapter presents the following content: Diaphragms, capacitive pressure sensor, fiber – optic pressure sensors, bellows, bourdon tube, manometers, resonant wire devices, electronic pressure gauges, special measurement devices for low pressures, high – pressure measurement, differential pressure-measuring devices, selection of pressure sensors.
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Lecture Sensors and analytical devices: Pressure measurement - Nguyễn Công Phương Nguyễn Công PhươngSensors and Analytical Devices Some Basic Measurement Methods, Pressure Measurement ContentsA. IntroductionB. Sensors CharacteristicsC. Some Basic Measurement MethodsD. Measurement Systems sites.google.com/site/ncpdhbkhn 2 Some Basic Measurement MethodsI. Sensor TechnologiesII. Temperature MeasurementIII.Pressure MeasurementIV.Flow MeasurementV. Level MeasurementVI.Mass, Force, and Torque MeasurementVII.Translational Motion, Vibration, and Shock MeasurementVIII.Rotational Motion Transducers sites.google.com/site/ncpdhbkhn 3 Pressure Measurement1. Introduction2. Diaphragms3. Capacitive Pressure Sensor4. Fiber – Optic Pressure Sensors5. Bellows6. Bourdon Tube7. Manometers8. Resonant Wire Devices9. Electronic Pressure Gauges10. Special Measurement Devices for Low Pressures11. High – Pressure Measurement12. Differential Pressure-Measuring Devices13. Selection of Pressure Sensors sites.google.com/site/ncpdhbkhn 4 Introduction (1)• Very commonly in most industrial process control systems, & the next-most measured process parameter after temperature.• Absolute pressure (a/abs): – The difference between the pressure of the fluid & the absolute zero of pressure. – Made for such purposes as aircraft altitude measuremen (altimeters) & when quantifying atmospheric pressure.• Gauge pressure (g): – The difference between the pressure of a fluid & atmospheric pressure. – Made by instruments such as those measuring the pressure in vehicle tires. Absolute pr. = Gauge pr. + Atmospheric pr.• Difference pressure (d): – The difference between two absolute pressure values. – For some purposes in industrial process, especially as part of some fluid flow rate-measuring devices. sites.google.com/site/ncpdhbkhn 5 Introduction (2)• Pressure = Force/Area• Unit: – SI: Pascal (Pa) = Newtons per square meter (N/m2) – 1bar = 10,000Pa – US & Canada: pounds per square inch (psi) – Sometimes: milimeter of mercury or milimeter of water (particularly for blood pressure) – For low pressure: torr; 1torr = 133.3Pa• To avoid ambiguity: – (a) or (abs) for absolute pressure: 2.50Pa (a) – (g) for gauge pressure: 10bar (g) – (d) for differential: 5bar (d) – US & Canada: psia, psig, psid sites.google.com/site/ncpdhbkhn 6 Pressure Measurement1. Introduction2. Diaphragms3. Capacitive Pressure Sensor4. Fiber – Optic Pressure Sensors5. Bellows6. Bourdon Tube7. Manometers8. Resonant Wire Devices9. Electronic Pressure Gauges10. Special Measurement Devices for Low Pressures11. High – Pressure Measurement12. Differential Pressure-Measuring Devices13. Selection of Pressure Sensors sites.google.com/site/ncpdhbkhn 7 Diaphragms (1) Translational movement Unknown pressure• Applied pressure causes displacement of the diaphragm & this movement is measured by a displacement transducer.• Different versions of diaphragm sensors can measure both absolute pressure (up to 50bar) & gauge pressure (up to 2000bar) according to whether the space on on side of the diaphram is, perspectively, evacuated or open to the atmosphere• A diaphragm can also measure differential pressure (up to 2.5bar) by applying the 2 pressures to the 2 sides of the diaphragm. sites.google.com/site/ncpdhbkhn 8 Diaphragms (2)• The diaphragm can be plastic, metal alloy, stainless steel, or ceramic.• Plastic diaphragms are the least expensive, but metal diaphragms give better accuracy.• Stainless steel is normally used in high temperature or corrosive environments.• Ceramic diaphragms are resistant even to strong acids & alkalis.• The typical magnitude of diaphragm displacement is 0.1mm. sites.google.com/site/ncpdhbkhn 9 Pressure Measurement1. Introduction2. Diaphragms3. Capacitive Pressure Sensor4. Fiber – Optic Pressure Sensors5. Bellows6. Bourdon Tube7. Manometers8. Resonant Wire Devices9. Electronic Pressure Gauges10. Special Measurement Devices for Low Pressures11. High – Pressure Measurement12. Differential Pressure-Measuring Devices13. Selection of Pressure Sensors sites.google.com/site/ncpdhbkhn 10 Capacitive Pressure Sensor• Simply a diaphragm-type device.• Diaphragm displacement is determined by measuri ...