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Digital Data Aquisition „Peeking into the Black Box“

Digital Data Aquisition „Peeking into the Black Box“. Lecture at the Department of Physical Chemistry Jan. 25 th 2002, J. Theiner Letzte Überarbeitung für Vorlesung 856-150, 6. Dez. 2004. originally. 0,52 Mol.l -1 Cl -. 1,22 ppb Pb. 0,11 mm.year -1. A Black Box. Why talk about that ?.

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Digital Data Aquisition „Peeking into the Black Box“

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  1. Digital Data Aquisition„Peeking into the Black Box“ Lecture at the Department of Physical ChemistryJan. 25th 2002, J. Theiner Letzte Überarbeitung für Vorlesung 856-150, 6. Dez. 2004 originally

  2. 0,52 Mol.l-1 Cl- 1,22 ppb Pb 0,11 mm.year-1 A Black Box .. digital data acquisition

  3. Why talk about that ? • Digital data and computer assisted processing are state of the art. • Everyone in science has to use methods and processes based upon • - but - • the basic concepts are rarely discussed and taught • predictible limitations and sources of error are frequently ignored • knowledge and understanding are essential for comparison and validation of available tools (e.g. software selection!) • .. layout and usage of „interfaces“ • analogue//analogue • anaolgue//digital • digital//digital digital data acquisition

  4. What is „Digital“ ? • Everything formed of a number of digits is a digital word • digit = symbol, character, letter ... • set of digits = alphabet, character set, alphanumeric code ... • Only a limited numberN of different digital words can be created from a set of m digits combined to form a word of n letters Among the unknown number of character sets ever invented and used by humans the most simple and general concept is the binary code (Boolean, Dual system) which can be used to encode any other digital information. digital data acquisition

  5. Resolution Digital Resolution - N increments Ecan be en/decoded to/from an analogue range ERange ERange Typical Values for ERange = 20 V (±10 V) 8 bit N = 256 DE = 78,43 mV 12 bit N = 4.096 DE = 4,884 mV 16 bit N = 65.536 DE = 305,2 µV 18 bit N = 262.144 DE = 76,29 µV 21 bit N = 2.097.152 DE = 9,537 µV 24 bit N = 16.777.216 DE = 1,192 µV DE digital data acquisition

  6. + Operationsverstärker +Vcc INPUT OUTPUT Vcc digital data acquisition

  7. RF R1 R2 U2  + Rn Un GND OP als Addierer Invertierende Grundschaltung: UIN +Vcc UOUT Summationspunkt ADDIERER: Vcc Spezialfall für Analogrechner: alle Ri gleich RF digital data acquisition

  8. RF R0 R2 R1 Rn-1  + GND DAC - Digital to Analogue Converter UREF UOUT digital data acquisition

  9. Linearity digital data acquisition

  10. FG output Ideal FG slope, 100 mV.sec-1 digital data acquisition

  11. FG output Current response on ideal FG-signal digital data acquisition

  12. FG output Digital FG output, 100 mV.sec-1 resolution: 152 µV.step-1 (16 bit, 10 V range) digital data acquisition

  13. FG output Current response on digital FG signal digital data acquisition

  14. FG output Current response on digital FG output detailed view digital data acquisition

  15. FG output .. But it can be worse: Effect of a poor performing potentiostat digital data acquisition

  16. FG output .. Which can produce absurd artefacts! digital data acquisition

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