On-Line Physical Measurements

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

10. Orifice Plate / Venturi Meter

11. 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

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

13. Thermocouples

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

16. V=I*R

17. 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

19. 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

20. 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

21. Pressure Measurement • Absolute • Gauge • Vacuum

23. Pressure Sensor Piezoelectric Sensor

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

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

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

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

28. 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

29. 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

30. Spectroscopy

31. Liquid / Gas Chromatography

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

33. 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

34. 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

35. 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