On-Line Physical Measurements

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On-Line Physical Measurements

• Terry A. Ring
• Department of Chemical Engineering
• University of Utah
• October 28, 2004

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Types of Instruments

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

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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

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Sight Flow Meter
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Rotameters
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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

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Temperature Measurement

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

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RTDs

• 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

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Thermistors

• Semiconductors made from mixtures of pure oxides
  (Mn, Ni, Cu, Zn, Fe, etc.) sintered at gt 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

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Thermocouples
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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

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Pressure Measurement

• Absolute
• Gauge
• Vacuum

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Liquid Density Measurement

• Hydrometers
• Weighing a fixed volume
• Oscillating Coriolis Densitometers
• Hydrostatic Densitometers
• Radiation Densitometers liquid/sludge
• Vibrating Densitometers Liq/sludge/gas

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Chemical Sensors

• Gas Analysis
• Electrochemical Analysis
• CO sensor
• alcohol sensor
• Ion mobility

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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

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On-Line Analytical Instruments

• Infra Red
• Gas Chromatography
• Liquid Chromatography
• Ultra Violet
• Visible
• How would each of these work?
• Time delays

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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

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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/(2N)
• 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

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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