Making Physical Measurements

On-Line Physical MeasurementsTerry A. RingDepartment of Chemical EngineeringUniversity of UtahTypes of InstrumentsFlow MeasurementLevel MeasurementTemperature MeasurementPressure MeasurementDensity MeasurementConcentrationAnalytical InstrumentationChemical SensorsSafety, Weight and Misc.On-Line ConnectionsAnalogue SignalmV, mA, Volts, Amp, Watts, otherAmplification to Industrial Std Scales4 to 20 mA+ 5 to -5 VDigitizationStep size = Scale/(2^N)N = bits in a byte of A-to-D boardCalculation Precision 8, 10, 12 16 digits or 32 digits of binary words are common

Flow MeasurementOrifice platesPitot tubesRotary FlowmetersMass Flowmeters Coriolis, ThermalMagnetic FlowmetersSight Flow Indicators paddleVariable-area Flowmeters rotametersVenturi TubesV-cone FlowmeterMany, many others

Sight Flow MeterRotametersTurbine Flow Meter

Thermal Mass Flow Meter

Orifice Plate / Venturi Meter

Level MeasurementFloat Level DevicesLevel GaugesDifferential Pressure Level DetectorsSlip tubes and DipsticksUltrasonic Level DetectorsLaser Level DetectorsLoad Cells on TanksMany, many othersTemperature MeasurementFilled-bulb, Glass-stem thermometerThermocouplesThermistorsResistance Temperature Detectors (RTDs)- platinum resistance thermometer PyrometersFiber-Optic ThermometersOthersThermocouples

Thermocouple

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

V=I*RRTDsBased on the electrical resistance of a conductor increasing with temperatureMost accurate, reproducible and stable thermal element availableRelatively expensiveVery preciseFragile but can be industrially hardened

ThermistorsSemiconductors made from mixtures of pure oxides (Mn, Ni, Cu, Zn, Fe, etc.) sintered at > 1800 oFVery good for narrow span measurementOutput highly non-linear, not good for wide span applications, fragile unless industrially hardenedSmall size, fast responseLack of stability at higher temperaturesPressure Measurement Bourdon pressure sensors- C Bourdon- Spiral Bourdon- Helical BourdonDifferential pressure instrumentsElectronic pressure sensors- strain gauge transducers- piezoelectric sensorManometersDiaphragm sensorsPressure MeasurementAbsoluteGaugeVacuum

Piezoelectric SensorPressure SensorLiquid Density MeasurementHydrometersWeighing a fixed volumeOscillating Coriolis DensitometersHydrostatic DensitometersRadiation Densitometers liquid/sludgeVibrating Densitometers Liq/sludge/gasHydrostatic DensitometersProcess Piping=P/(g h)25Radiation Densitometerh

Radiation or LightX-raysBeers LawI/Io= exp(-kcL)

Chemical SensorsGas AnalysisElectrochemical AnalysisCO sensoralcohol sensorIon mobility

Drift Cell Analysistime the ions spend in the drift cell td can be obtained in terms of P/V.L = length of cellV= Voltagevd = drift velocityKo= mobilityP, 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 ChargeOn-Line Analytical InstrumentsInfra RedGas ChromatographyLiquid ChromatographyUltra VioletVisibleMass Spectrometer Mw 1 to 60 or 1 to 300.

How would each of these work?Time delaysSpectroscopy

Liquid / Gas Chromatography

Mass Spectroscopy

Mw=106.12 gm/moleCapillaryVacProcessSafety, Weight and Misc.Relief ValvesRupture DiscsLeak Detectors -Anemometers air and gas flowsBoroscopes inspect remote or limited-access locations reactors, process lines, etc. (fiberscopes)Weighing Electronic Load CellsOn-Line ConnectionsAnalogue SignalmV, mA, Volts, Amp, Watts, otherAmplification to Industrial Std Scales4 to 20 mA+ 5 to -5 VDigitizationStep size = Scale/(2^N)N = bits in a byte of A-to-D boardCalculation Precision 8, 10, 12 16 digits or 32 digits of binary words are common

Keep it Running Well KNOW YOUR EQUIPMENTAccuracy and PrecisionUNDERSTAND THE LIMITATIONS OF YOUR EQUIPMENT CALIBRATE AS MUCH AS IS REASONABLE Maintain Equipment so it will Perform Reliably