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Pressure Transducers

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  1. Pressure Transducers • Absolute / Gauge / Differential • Force collector principle: • Manometer • Strain-gauge • Capacitive • Piezoelectric • Other principles: • Bourdon tube • Acoustic

  2. Pressure Units As usual SI units are recommended although some deprecated unit of measurements are still being used in specific fields... ...but the most important distinction to be made while talking about pressure is pressure measurement TYPE itself, since it can lead to misunderstandings difficult to point out...

  3. Absolute / Gauge / Differential Pressure Measurements Absolute pressure • Referred to ideal vacuum Gauge pressure • Referred to actual atmospheric pressure close to the transducer Differential pressure • Difference between two points Sealed gauge • Referred to atmospheric pressure at sea level in standard condition

  4. Force Collector Principle A first mechanical element converts a pressure difference into a force • Transducers created in this way are close relatives to force transducer and presents the same advantages and disadvantages (eg. II order...) • Black box calibration corrects any geometrical imperfection of surfaces Affected surface Force transducer pressure force

  5. Manometers • Based on hydrostatic equilibrium between two liquid columns subject to different pressure • Commonly used in most static applications when data recording is not required • P0 can be sealed for absolute measurements or open to allow for differential or gauge measurement • Liquid choice depends on working condition and temperature ranges In general: p2-p1=ρHg


  6. Manometers • Come in different configurations: inclined for sensitivity amplification or with a wider reservoir to decrease reference point sensitivity • Commonly used liquids are mercury (for its high density) and water (for its availability) p1=p2+γmIsin(α)

  7. Manometers • Advantages: • Cheapness • Reliability • Direct differential measurement • Disadvantage: • Difficult to record electrically • High settling time • Narrow measuring range • Fluid used can alter measurand

  8. Strain gauge pressure transducer • Based on the force collector principle • Bandwidth and sensitivity depends on the actual stiffness of the elastic medium • Require bridge conditioning • Static and quasi-statics measurement • Linear up to a wide portion of yelding limit of the elastic medium • see force transducers for details Force collector Elastic medium PRESSURE FORCE DEFORMATION

  9. Strain gauge pressure transducer

  10. Capacitive pressure transducer • Based on the force collector principle • Low bandwidth limit • Static or quasi-static response • Require no conditioning • High accuracy (linearity lower than 1%) • Inaccurate on low measuring range • see force transducers for details Force collector Moving probe PRESSURE FORCE DISPLACEMENT

  11. Piezoelectric pressure transducer • Based on the force collector principle • High bandwidth limit • No static or quasi-static response • Require ICP/IEPE conditioning • High accuracy (linearity close to 1%) • Sensible to acceleration • see force transducers for details Force collector Quartz crystal PRESSURE FORCE COMPRESSION

  12. Bourdon tube • Based on a oval tube that tends towards a cylindrical shape thanks to inside pressure • both for gas and liquids • up to 100MPa • 0.1% accuracy

  13. Acoustic pressure transducer • Based on the acoustic wave transmission on a gaseous medium depending on pressure • Requires per gas calibration in full range • Requires actual excitation and transmission • High frequency response (up to 10kHz) • Full scale up to 20 kPa • Very low loading effect • No static or quasi-static measurements