Peter Keusch, University of Regensburg
German version
- with the possible exceptions of handguns and tequila."
Mitch Ratliffe in Technology Review
 Fig. 1: CASSY-E Interface |
The CASSY System (Computer Assisted Science System) consists of two different components:
· The application independent components - connector card, ribbon cable and the CASSY INTERFACE - represent the basic conditions for a computer-aided data logging. · The application dependent components are specific to the needs of the different measurements: sensors (conductivity measurement cell, pH electrode, temperature sensor), data acquisition boxes (measuring modules) and the required program diskettes (Conductivity, pH, Temperature, Multimeter, Poisson). |
The inputs A/D of the INTERFACE are analogue inputs for DC voltage and alternating voltage. The inputs A and D are the slots for the measuring- and sensor-boxes. The boxes are supplied with voltage by contact connections. Additionally the boxes are controlled and identified by these inputs via the software The measuring range (± O.3V, ± 1V, ± 3V, ± 10V, ± 30V) is selected at the inputs B and C. Only constant ± 10V is taken at the inputs A and D.
Positive aspects
· Problem free calibration of the sensors (Temperature sensor, conductivity measuring cell, pH sensor, redox probe)
· While calibrating the conductivity sensor the reaction temperature is taken into account.
· Choice of data logging time intervals (Program: Measuring and Evaluating / Multimeter)
· Choice of measuring ranges and recording time (Program: Conductivity / Kinetics)
· Choice of measuring ranges and of data logging time intervals (Program: Temperature)
· Output of the data table
· Commercial measuring instruments provided with a voltage output (e.g. photometer) can be used problem-free (Program: Measuring and Evaluating / Multimeter)
· Entering of measurement series (recorded without computer support) via keybord
· Cassy provides a variety of options for analysis of measured data. The graphic analysis in diagrams is very comfortable:
- Displaying of data points either as crosses or as points, connected by lines
- Elimination of 'outliers'
- Overlay of up to ten graphs in a multigraph screen
- Overlay of a coordinate grid
- Large-scale display of a defined portion of a curve
- Conversion of the measured data by entering the appropriate formula (Programs: Conductivity / Kinetics, Measuring and Evaluating / Multimeter)
- Determination of equivalence points in titrations (Programs: Conductivity, pH) and pka values (Program: pH)
- Highlighting of the linear portion of a graph, drawing of a "best fit straight line" through "noisy" data points, output of the slope and of the y-intercept (Programs: Conductivity / Kinetics, Measuring and Evaluating / Multimeter)
- Determination of the activation energy (Program: Conductivity / Kinetics)
- Highlighting and calculation of a defined area below a curve (Program: Measuring and Evaluating / Multimeter)
- Optimization and selectable conversion of the graph axes (Program: Measuring and Evaluating / Multimeter)
Critical aspect:
· If conductivity is measured continuously, the data will be logged automatically at 0.5 s intervals. A subsequent elimination of a great number of data pairs is a very laborious undertaking. Each data pair must be deleted individually in the value table.
For this reason, it is necessary at times, to transfer the CASSY value table into a Microsoft Excel Spread sheet. Excel's statistical capabilities are impressive, and its graphical possibilities are virtually unlimited.
Conversion of CASSY files to Microsoft Excel files:
CASSY provides a program file 'Diftrans.exe' and the appropriate configuration file 'Diftrans.cfg' for the conversion of CASSY-files to Excel files on the discette 'CASSY test'. The two files should be stored on the hard disk. When the file 'Diftrans.exe' is open, one inputs via 'File name:' the complete designation of the CASSY file e.g. \CASSY\ESTER\ETAC_39.DL3 and affirms using the RETURN key.
After opening the appropriate file in MS Excel via the file type 'data exchange format', the file can be stored. When importing further tables, MS Excel generates a new spreadsheet for each table. Individual table pages can be summarized in a single page by shifting. This is effected via the menu instruction 'Edit ® 'Move or Copy Sheet...' .
A dialog module programmed in Visual Basic permits the hiding of data pairs in the data sheet, so that e.g. only every tenth data point can be plotted in the appropriate graph. The hidden data pairs are not deleted. They are available in the background and are taken into account in calculations performed in the Excel table.
CASSY-S
CASSY-S represents the new generation of the Computer Assisted Science SYstem - Leybold Didactic
Interface Sensor-CASSY - Experiment Set-up: Photometric Measurements
Software: CASSY Lab (Manual Download)
Peter Keusch Computergestützte Experimente
Kinetics:
Catalyzed Iodination of AcetoneObjectives: Test for a Pseudo First Order Behaviour, Determination of Rate Constants and Activation Parameters | Experiment Description |
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Alkaline Hydrolysis of Esters Objectives: Test for a Second Order Behaviour, Determination of Rate Constants and Activation Parameters | Experiment Description |
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Catalyzed Decomposition of Hydrogen Peroxide Objectives: Test for a First Order Behaviour, Determination of Rate Constants and Activation Parameters | Experiment Description |
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Enzymatic Decomposition of Hydrogen Peroxide Objectives: Dependance of Reaction Rate on Temperature and on Concentration of Enzyme or Substrate, First Order Reaction | Experiment Description |
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Hydrolysis of t-Butyl Chloride Objectives: Test for a First Order Behaviour, Determination of Rate Constants and Activation Parameters | Experiment Description |
Electrochemistry:
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Lead-acid Battery (Model) Objectives: Estimation of Voltage, Current and Time during Discharge or Charge, Determination of the Capacity and the Battery Efficiency | Experiment Description |
Radioactivity:
| Decay of Protactinium-234m Objective: Determination of the Half-Life, Background Radiation |
Experiment Description |
Dyes:
| Light Absorption of Cyanidin Objectives: Determination of the Absorption Maxima of Cyanidin and its Metal Complexes |
Experiment Description |
| Light Absorption of Triphenylmethane Dyes Objectives: Determination of the Absorption Maxima - Triphenylmethyl Cation, Crystal Violet, Malachite Green, Fuchsin, protonated Crystal Violet and N-substituted Fuchsin |
Experiment Description |
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Negative Solvatochromism Objectives: Shift of the Spectrum, Solvent Polarity |
Experiment Description |
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Positive Solvatochromism Objectives: Shift of the Spectrum, Solvent Polarity |
Experiment Description |
