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On-Line Physical Measurements. Terry A. Ring Department of Chemical Engineering University of Utah October 28, 2004. Types of Instruments. Flow Measurement Level Measurement Temperature Measurement Pressure Measurement Density Measurement Concentration Analytical Instrumentation
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On-Line Physical Measurements Terry A. Ring Department of Chemical Engineering University of Utah October 28, 2004
Types of Instruments • Flow Measurement • Level Measurement • Temperature Measurement • Pressure Measurement • Density Measurement • Concentration • Analytical Instrumentation • Chemical Sensors • Safety, Weight and Misc.
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
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
Temperature Measurement • Filled-bulb, Glass-stem thermometer • Thermocouples • Thermistors • Resistance Temperature Detectors (RTDs)- platinum resistance thermometer • Pyrometers • Fiber-Optic Thermometers • Others
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
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
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
Pressure Measurement • Absolute • Gauge • Vacuum
Liquid Density Measurement • Hydrometers • Weighing a fixed volume • Oscillating Coriolis Densitometers • Hydrostatic Densitometers • Radiation Densitometers – liquid/sludge • Vibrating Densitometers – Liq/sludge/gas
Chemical Sensors • Gas Analysis • Electrochemical Analysis • CO sensor • alcohol sensor • Ion mobility
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
On-Line Analytical Instruments • Infra Red • Gas Chromatography • Liquid Chromatography • Ultra Violet • Visible • How would each of these work? • Time delays
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
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
CONCLUSIONS • 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