Making Physical MeasurementsOVERVIEWExperimentsImportant TermsRandom Error SourcesSystematic Error SourcesSlide 7Slide 8Slide 9Potential ProblemsWHAT PRECISION IS REQUIRED?CalibrationTypes of InstrumentsLiquid Density MeasurementAnalytical InstrumentationTypes of AnalysisAnalytical StrategiesSlide 18Slide 19Making Physical Making Physical MeasurementsMeasurementsTerry A. RingTerry A. RingDepartment of Chemical Department of Chemical EngineeringEngineeringUniversity of UtahUniversity of Utah22 August 200522 August 2005OVERVIEWOVERVIEW•Course experiments – general Course experiments – general approach to making physical approach to making physical measurementsmeasurements•Terminology Terminology •CalibrationCalibration•Types of InstrumentsTypes of Instruments•Class ParticipationClass ParticipationExperimentsExperiments•Preparation for an experimentPreparation for an experiment- organization – teamwork- organization – teamwork- time management- time management•Equipment/apparatusEquipment/apparatus- keep detailed list of equipment/chemicals- keep detailed list of equipment/chemicals- know your equipment/capabilities- know your equipment/capabilities- most equipment expensive, do not abuse - most equipment expensive, do not abuse or neglector neglectImportant TermsImportant Terms•Error – the difference between the Error – the difference between the “true value” and the observed “true value” and the observed (measured) value(measured) value•Random error – fluctuations in the Random error – fluctuations in the measured value due to repeated measured value due to repeated measurementsmeasurements•Systematic error – all measured values Systematic error – all measured values are off by the same amount due to a) are off by the same amount due to a) incorrect calibration b) faulty incorrect calibration b) faulty equipment c) other causesequipment c) other causes•Illegitimate error – erroneous Illegitimate error – erroneous method/technique, goofsmethod/technique, goofsRandom Error SourcesRandom Error Sources•Judgement errors, estimate errors, Judgement errors, estimate errors, parallaxparallax•Fluctuating ConditionsFluctuating Conditions•DigitizationDigitization•Disturbances such as mechanical Disturbances such as mechanical vibrations or static electricty vibrations or static electricty caused by solar activitycaused by solar activity•SamplingSamplingSystematic Error SourcesSystematic Error Sources•Calibration of instrumentCalibration of instrument•Environmental conditions different Environmental conditions different from calibrationfrom calibration•Technique – not at equilibrium or at Technique – not at equilibrium or at steady state.steady state.•SamplingSampling22tmeasuremensamplingTotalImportant TermsImportant Terms•Accuracy - a measure of how close the Accuracy - a measure of how close the result comes to the “true value” result comes to the “true value” (correctness). An indication of how well we (correctness). An indication of how well we control systemic errors.control systemic errors.•Precision – a measure of how exactly the Precision – a measure of how exactly the result is determined (reproducibility) – no result is determined (reproducibility) – no relation to “true value”. An indication of relation to “true value”. An indication of how well we overcome or analyze random how well we overcome or analyze random errorserrors•Limit of detection – smallest value which Limit of detection – smallest value which can be detected.can be detected.Important TermsImportant Terms•Discrepancy – the difference Discrepancy – the difference between values for the same between values for the same measurementmeasurement•Uncertainty – an estimate of the Uncertainty – an estimate of the range in the error. Always range in the error. Always determined for a particular determined for a particular confidence level, i.e.confidence level, i.e.)%95( levelconfidenceyyy ExperimentsExperiments•Literature workLiterature work- understand theory/principles/concepts from - understand theory/principles/concepts from textbooks and referencestextbooks and references• ReferencesReferences- textbook- textbook- Perry’s chemical engineers handbook- Perry’s chemical engineers handbook- CRC handbook of chemistry/physics- CRC handbook of chemistry/physics- Instrument Engineers’ Handbook- process - Instrument Engineers’ Handbook- process measurement and analysis – B.G. Liptak, ed.measurement and analysis – B.G. Liptak, ed.- Web sites- Web sitesPotential ProblemsPotential Problems•ParalaxParalax•Scale InterpretationScale Interpretation•Appropriate ScaleAppropriate Scale•Appropriate InstrumentAppropriate Instrument–Appropriate detection limitsAppropriate detection limits–Signal to Noise ratioSignal to Noise ratio–Appropriate Accuracy and PrecisionAppropriate Accuracy and Precision•Significant FiguresSignificant FiguresWHAT PRECISION IS WHAT PRECISION IS REQUIRED?REQUIRED?•Overall PrecisionOverall Precision•Impact on CalculationImpact on Calculation•Difficulty of MeasurementDifficulty of MeasurementCalibrationCalibration•Should use primary standards if possibleShould use primary standards if possible•Calibrate as close to measuring conditions as Calibrate as close to measuring conditions as possiblepossible•Sometimes performed at Sometimes performed at –the factorythe factory–Professional laboratoriesProfessional laboratories•Laboratory standards Laboratory standards ice bath, constant temp bathice bath, constant temp bath•Tabulated properties and relationshipsTabulated properties and relationshipsboiling water at barometric pressureboiling water at barometric pressuretriple point of watertriple point of water•Linear vs Non-linear Calibration curvesLinear vs Non-linear Calibration curvesTypes of InstrumentsTypes of Instruments•Off-line Process InstrumentationOff-line Process Instrumentation•Density MeasurementDensity Measurement•Weight and Misc. SensorsWeight and Misc. Sensors•Analytical InstrumentationAnalytical Instrumentation–Issues Issues •SamplingSampling–Grab sampleGrab sample–Statistical SamplingStatistical Sampling•Sample PreparationSample Preparation–Splitting, extraction, decompositionSplitting, extraction, decomposition•On–line InstrumentationOn–line Instrumentation–Flow