METR3613-L3 - METR 3613 Meteorological Measurement Systems...

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8/27/2007 METR 3613 - Lecture 3 METR 3613: Meteorological Measurement Systems Fall 2007 Dr. Petra Klein Lecture 3: Important Definitions Copyright © 2004, Board of Regents of the University of Oklahoma. All Rights Reserved.
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8/27/2007 METR 3613 - Lecture 3 Outline ± Important definitions ± Functional model of a measurement system ± Sources of errors and standards
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8/27/2007 METR 3613 - Lecture 3 Important Definitions ± Measurand: ² Measured quantity (e.g. temperature or wind speed) ± So in other words: the stuff that we want to measure! ² Sensor input ² Can never be determined exactly , because there are always errors associated with measurements
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8/27/2007 METR 3613 - Lecture 3 Important Definitions ± What is the difference between a sensor and an instrument??????? ± Sensor: ² An element that receives energy from the measurand (input) and produces an output signal that is related to the input ² Possible input: ± Air temperature, wind speed ² Possible output: ± e.g. resistance, voltage, mechanical deflection, rotation rate ² Extracts energy from the measured medium and adds noise to the signal perfect measurement is impossible
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8/27/2007 METR 3613 - Lecture 3 Important Definitions ± Instrument: ² Sensor plus any other required transducers, and a data display element ² E.g.: Mercury in-glass thermometer is it a sensor or an instrument??? ± Instrument because the column of mercury and attached scale function as data display ± Data display ² Any mechanism for displaying data to the user ± Transducer ² Converts energy from one form to another ² All sensors are transducers, but not all transducers are sensors
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Important Definitions ± Signal: ² An information bearing quantity ± E.g.: Voltage proportional to temperature is a signal that conveys information about temperature ± If the frequency of a voltage signal is proportional to the measurand, then only the frequency contains information but not the voltage itself ² Analog signal ± Information is continuously proportional to the measurand ± Measurand and also most raw sensor outputs are analog ² Digital Signal ± A signal whose information content varies in discrete steps ± The smaller the step size the closer the digital signal resembles the analog signal ± Granularity of a digital signal can always be reveled if it is examined in detail
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8/27/2007 METR 3613 - Lecture 3 Important Definitions ± Signal conditioning ² Operations that ± convert signal from one form to another ² e.g. from resistance to voltage, ± increase amplitude ² i.e. apply a gain to raw output, ± reduce noise ² Typically done by filtering ± compensate for side effects ² e.g. temperature sensitivity of a pressure sensor
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8/27/2007 METR 3613 - Lecture 3 Functional model Analog signal conditioning Analog-to- digital converter Digital signal conditioning
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8/27/2007 METR 3613 - Lecture 3 Mercury-in-Glass Thermometer Heat energy is converted into a change in volume of the mercury in the bulb Amplification of the signal depending on the diameter of the column relative to the volume of the bulb
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This note was uploaded on 04/08/2008 for the course METR 3613 taught by Professor Klien during the Fall '07 term at The University of Oklahoma.

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METR3613-L3 - METR 3613 Meteorological Measurement Systems...

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