CHEM3440Lec1F06 - The Analysis Concept What is it? How much...

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CHEM*3440 Chemical Instrumentation Topic 1 Concept of the Instrument The Analysis Concept What is it? How much is there? How does it behave? Sample for Analysis Probe Electrons, photons, atoms, molecules, ions, heat, . .. Response Heat, ions, molecules, atoms, photons, electrons, . .. An Instrument Controls the applied probe Measures the system ! s response Instrument Encodes Data Transformation The Physical and Chemical Domain The Analyst’s Domain Data Domains Physical and Chemical Domain Current Power Voltage Charge Number Scale Position Non-Electrical Domains Electrical Domains
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Analyst seeks to measure physical or chemical property of a system. Instrument creates an electrical signal to represent datum. Data proceeds through instrument; different transducers convert signal from one domain to another. Analysis of instrument behaviour: characterized as a sequence of data domain conversions, each analyzed separately. Transducers Input Transducer : converts data from non-electrical to electrical domain. Output Transducer : converts data from electrical to non- electrical domain. A thermocouple generates a specific voltage at a certain temperature. It is a temperature-to-voltage input transducer. A stepper motor running a pen on a chart recorder moves the pen in response to a current flow. It is a current-to-position output transducer. Example: The Thermocouple Temperature - to - Voltage transducer. Connect two dissimilar metals appropriately. Thermoelectric effect produces voltage difference which depends upon the temperature difference between the two junctions. Reference Temperature Sample Temperature Metal #2 Metal #1 Metal #1 ! V Thermocouple con’t 1 Voltage depends on temperature difference (T m - T r ). Relationship is called the transfer function. T r is almost always 0 ˚C. Transfer is generally modeled as f T m ! T r ( ) = A T m ! T r ( )+ B T m ! T r ( ) 2 + C T m ! T r ( ) B and C often ignored. Linear transfer function. Popular thermocouple called K-type (two metals are chromel
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This note was uploaded on 05/15/2010 for the course CHEM 3440 taught by Professor Danthomas during the Fall '06 term at University of Guelph.

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CHEM3440Lec1F06 - The Analysis Concept What is it? How much...

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