On-Line Physical Measurements-1
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Transcript On-Line Physical Measurements-1
On-Line Physical Measurements
Terry A. Ring
Department of Chemical Engineering
University of Utah
Types of Instruments
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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, 12
16 digits or 32 digits of binary
words are common
Flow Measurement
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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
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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
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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 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
Pressure Sensor
Piezoelectric Sensor
Liquid Density Measurement
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Hydrometers
Weighing a fixed volume
Oscillating Coriolis Densitometers
Hydrostatic Densitometers
Radiation Densitometers – liquid/sludge
Vibrating Densitometers – Liq/sludge/gas
Hydrostatic Densitometers
ρ=ΔP/(g h)
Process Piping
Radiation Densitometer
Radiation β or γ
Light
X-rays
Beer’s Law
I/Io= exp(-kcL)
hυ
Chemical Sensors
• Gas Analysis
– Electrochemical Analysis
• CO sensor
• alcohol sensor
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Surface Electrodes:
Fired-On
Silver Paste
Doped
Nickel Oxide
Thin Film
0.5 um
Film
Thickness
2.5 mm
2 mm
3 mm
1 mm
2.5 mm
1 mm
10 mm
– Ion mobility
Silver Lead
Wires
Alumina Substrate
+
Micro-Weld
Drift Cell Analysis
• time the ions spend in the
drift cell td can be obtained
in terms of P/V.
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L = length of cell
V= Voltage
vd = drift velocity
Mobility
Ko= mobility
P, T = Pressure and Temperature,
subscript o is on-line conditions,
without subscript is inside instrument
(typically vacuum)
• Create Ions by Plasma
depends on MW and Charge
On-Line Analytical Instruments
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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
Vac
Capillary
Mw=106.12 gm/mole
Process
Safety, Weight and Misc.
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Relief Valves
Rupture Discs
Leak Detectors Anemometers – air and gas flows
Boroscopes – inspect remote or limitedaccess 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
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