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 Safety, Weight and Misc.

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, digits or 32 digits of binary words are common

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

Sight Flow Meter

Rotameters

Turbine Flow Meter

Thermal Mass Flow Meter

Orifice Plate / Venturi Meter

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

Thermocouples

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

V=I*R

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 o F 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

Piezoelectric Sensor Pressure Sensor

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

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

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

Chemical Sensors Gas Analysis –Electrochemical Analysis CO sensor alcohol sensor –Ion mobility

Drift Cell Analysis time the ions spend in the drift cell t d can be obtained in terms of P/V. L = length of cell V= Voltage vd = drift velocity K o = 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

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

Spectroscopy

Liquid / Gas Chromatography

Mass Spectroscopy Mw= gm/mole Capillary Vac Process

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, digits or 32 digits of binary words are common

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