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Pressure Measurements

Pressure Measurements. Absolute, Gauge, and Differential Barometers Manometers Low/High Level Analog Output Calibration. Pressure Ranges. Ref. Press. Absolute Pressure. P abs = 0 : When all molecular action stops. P abs = P gage + P ambient.

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Pressure Measurements

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  1. Pressure Measurements • Absolute, Gauge, and Differential • Barometers • Manometers • Low/High Level Analog Output • Calibration

  2. Pressure Ranges

  3. Ref. Press Absolute Pressure Pabs = 0 : When all molecular action stops. Pabs = Pgage+ Pambient Pabs – Pressure that is used in thermodynamics to determine the state of a substance. Pgage – It is the pressure relative to the local ambient air pressure Differential pressure – Diff. Pressure is simply the diff. In pressure between two points

  4. Differential Pressure P2 P1

  5. Manometerdifferential P1 P2 P2 – P1 = (m- s) g h m Density of manometer fluid s -Density of sensed fluid (P/ g) – height of fluid-(height of Hg) Density vs temperature Thermal expansion For gases, s is zero P1 A A h h P2 A

  6. Manometer differential P1 P1 A A h P2 h P2 A

  7. Inclined Manometerdifferential For low pressure differentials, use Inclined manometer Increased sensitivity and accuracy P1 P1 A hr h P2 g A P2 A

  8. Barometerabsolute 0 • Well type manometer with one leg evacuated (to make it Hg vapor pressure) • Pabs = gh •  density • g acceleration due to gravity • h height of the fluid P=0 A h h Patm Patm A

  9. Gauge Pressure Patm P2

  10. Very High Accuracy Millivolt Output Pressure TransducerPX01-MV

  11. SPECIFICATIONS: Excitation: 10 Vdc (15Vdc max) Output: 3 mV/V ±0.25% Input Resistance: 350 Ω±5 PΩ Output Resistance: 350 ±5 Ω Linearity: ±0.05%FS Hysteresis: ±0.05% FS Repeatability: ±0.05% FS Zero Balance: 1.0% FS Agency Approvals: Standard: FM Intrinsically Safe IS/I.II.III/1/CDEFG Optional: FM Hazardous Location S/I/1/ABCD Shunt Calibration: Value specified on Calibration sheet Sensing Element: 4 active-arm bridge, using thick film strain gages in a hermetically sealed chamber Operating Temp Range: -73 to 163°C (-100 to 325°F) Compensated Temp Range: 16 to 71°C (60 to 160°F) Thermal Effects: Span: 0.0025% Rdg/°F Zero: 0.0025% FS/F

  12. Gain

  13. Low Pressure Transducer for Vacuum/Differential/Gage for Measurements of Clean GasesPX160 Series

  14. SPECIFICATIONS: Excitation: 8 Vdc Regulated (6 to 12 Vdc at 20 mA) PX163-120BD5V use 10Vdc Output: 1 to 6 Vdc Linearity: ±1.0% FS BFSL at specified voltage Hysteresis & Repeatability: ±0.25% full scale Zero Balance: 1 Vdc ± 0.05 (3.5± 0.05 Vdc PX163 series) Operable Temperature Range: -40 to 185°F (-40 to 85°C) Compensated Temperature Range: PX161 and PX162: 0 to 145°F (-18 to 63°C) PX163 and 164: 41 to 113°F (5 to 45°C) Operable Overpressure: 5 psi Media Compatibility P1: Dry Gases Only

  15. Block Diagram Data Acquisition Card Vex Computer Breakout Mux Amp A/D PX01-MV PX160 Series +Vex

  16. Calibrationnegative differential Patm Transducer Patm P1 h

  17. Calibrationpositive differential Patm Transducer Patm P1 h

  18. CalibrationP<Pa absolute Transducer Patm P=0 P1 h1 hatm Patm hg

  19. Bourdon gauge

  20. Piezo-resistive pressure sensors Pressure causes stress Stress changes resistance

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