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On-Line Physical Measurements

On-Line Physical Measurements. Terry A. Ring Department of Chemical Engineering University of Utah. Types of Instruments. Flow Measurement Level Measurement Temperature Measurement Pressure Measurement Density Measurement Concentration Analytical Instrumentation Chemical Sensors

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On-Line Physical Measurements

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  1. On-Line Physical Measurements Terry A. Ring Department of Chemical Engineering University of Utah

  2. Types of Instruments • Flow Measurement • Level Measurement • Temperature Measurement • Pressure Measurement • Density Measurement • Concentration • Analytical Instrumentation • Chemical Sensors • Safety, Weight and Misc.

  3. On-Line Connections • Analogue Signal • mV, mA, Volts, Amp, Watts, other • Amplification to Industrial Std Scales • 4 to 20 mA • + 5 to -5 V • Digitization • Step size = Scale/(2^N) • N = bits in a byte of A-to-D board • Calculation Precision 8, 10, 12 16 digits or 32 digits of binary words are common

  4. Flow Measurement • Orifice plates • Pitot tubes • Rotary Flowmeters • Mass Flowmeters – Coriolis, Thermal • Magnetic Flowmeters • Sight Flow Indicators – paddle • Variable-area Flowmeters – rotameters • Venturi Tubes • V-cone Flowmeter • Many, many others

  5. Sight Flow Meter

  6. Rotameters

  7. Turbine Flow Meter

  8. Thermal Mass Flow Meter

  9. Orifice Plate / Venturi Meter

  10. Level Measurement • Float Level Devices • Level Gauges • Differential Pressure Level Detectors • Slip tubes and Dipsticks • Ultrasonic Level Detectors • Laser Level Detectors • Load Cells on Tanks • Many, many others

  11. Temperature Measurement • Filled-bulb, Glass-stem thermometer • Thermocouples • Thermistors • Resistance Temperature Detectors (RTDs)- platinum resistance thermometer • Pyrometers • Fiber-Optic Thermometers • Others

  12. Thermocouples

  13. Thermocouple Fermi – Dirac Distribution µ=Fermi Level or 50% fill level µ=Chemical Potential of electron

  14. V=I*R

  15. RTD’s • Based on the electrical resistance of a conductor increasing with temperature • Most accurate, reproducible and stable thermal element available • Relatively expensive • Very precise • Fragile but can be industrially hardened

  16. Thermistors • Semiconductors made from mixtures of pure oxides (Mn, Ni, Cu, Zn, Fe, etc.) sintered at > 1800 oF • Very good for narrow span measurement • Output highly non-linear, not good for wide span applications, fragile unless industrially hardened • Small size, fast response • Lack of stability at higher temperatures

  17. Pressure Measurement • Bourdon pressure sensors- C Bourdon- Spiral Bourdon- Helical Bourdon • Differential pressure instruments • Electronic pressure sensors- strain gauge transducers- piezoelectric sensor • Manometers • Diaphragm sensors

  18. Pressure Measurement • Absolute • Gauge • Vacuum

  19. Pressure Sensor Piezoelectric Sensor

  20. Liquid Density Measurement • Hydrometers • Weighing a fixed volume • Oscillating Coriolis Densitometers • Hydrostatic Densitometers • Radiation Densitometers – liquid/sludge • Vibrating Densitometers – Liq/sludge/gas

  21. Hydrostatic Densitometers ρ=ΔP/(g h) Process Piping

  22. Radiation Densitometer Radiation β or γ Light X-rays Beer’s Law I/Io= exp(-kcL) hυ

  23. Chemical Sensors • Gas Analysis • Electrochemical Analysis • CO sensor • alcohol sensor • Ion mobility

  24. Drift Cell Analysis • time the ions spend in the drift cell td can be obtained in terms of P/V. • L = length of cell • V= Voltage • vd = drift velocity • Ko= mobility • P, T = Pressure and Temperature, subscript o is on-line conditions, without subscript is inside instrument (typically vacuum) • Create Ions by Plasma Mobility depends on MW and Charge

  25. On-Line Analytical Instruments • Infra Red • Gas Chromatography • Liquid Chromatography • Ultra Violet • Visible • Mass Spectrometer Mw 1 to 60 or 1 to 300. • How would each of these work? • Time delays

  26. Spectroscopy

  27. Liquid / Gas Chromatography

  28. Mass Spectroscopy Vac Capillary Mw=106.12 gm/mole Process

  29. Safety, Weight and Misc. • Relief Valves • Rupture Discs • Leak Detectors - • Anemometers – air and gas flows • Boroscopes – inspect remote or limited-access locations – reactors, process lines, etc. (fiberscopes) • Weighing – Electronic Load Cells

  30. On-Line Connections • Analogue Signal • mV, mA, Volts, Amp, Watts, other • Amplification to Industrial Std Scales • 4 to 20 mA • + 5 to -5 V • Digitization • Step size = Scale/(2^N) • N = bits in a byte of A-to-D board • Calculation Precision 8, 10, 12 16 digits or 32 digits of binary words are common

  31. Keep it Running Well • KNOW YOUR EQUIPMENT • Accuracy and Precision • UNDERSTAND THE LIMITATIONS OF YOUR EQUIPMENT • CALIBRATE AS MUCH AS IS REASONABLE • Maintain Equipment so it will Perform Reliably

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