Data Acquisition & Analysis

Purpose: This is an "open-ended" laboratory that you do in conjunction with another 565 laboratory. The individual steps will vary depending on which instrument you choose to interface. But each will follow the same basic outline. The basic task is to use an analog-to-digital (A/D) converter board, with its associated software, both present in the computer, to analyze data from a scientific instrument. You will use the computer instead of the hard-copy recording device to obtain the data. Subsequent data analysis can be more accurate. This will give you experience in computer data acquisition and analysis, and also allow more extensive data analysis. You should allow 2 weeks to complete this combined experiment, which will also simultaneously complete one of instrumental experiments.

Equipment: One of the Analytical Labs Computers with A/D board and LabView software; plus the scientific instrument of your choice in the Instrumental Analysis Laboratory (with the exception of the FTIR and vis-UV spectrophotometer, which are already computer interfaced).

Software: The software manuals have detailed instructions concerning the software. Manuals are quite ddetailed and students could spend a lot of time finding the appropriate information. It is best to consult the teaching assistant for operating instructions.

Procedure Summary -

1. Determine the signal and noise characteristics of the instrument/experiment that you have chosen. This is required to know what voltage range to use for the A/D board, and what computer signal filtering may be required.
   
   
2. Connect the positive instrument output to the screw labeled CH0 and the negative output to the CH8/0 RET screw on the screw terminal board for the A/D. If there is a third (ground) output, connect it to any of the screws labeled 8 GND. Set up the LabView software to collect the data on the computer and run the experiment.
   
   
3. Use the a spread sheet program, such as Excell or Quattro, to analyze the data in the appropriate fashion, including any appropriate filtering of the data to reduce noise.
   
   
4. Submit the usual report and answers to questions required for the specific experiment. This will satisfy the requirement for the laboratory that you chose. In addition, submit a separate report for this computer experiment describing the acquisition and analysis procedures that you followed, the instrument signal characteristics, the A/D board settings that you used (just voltage range, sampling rate, and sampling time), and the advantages and disadvantages of computer-based analysis versus the usual methods. Include answers to the questions.

Questions:

1. What effects did your digital (computer) filtering steps have on the data? How do the effects compare qualitatively to analog (op-amp) filtering? Give the theoretical mathematical relationships that describe how the data was filtered and explain their effect on the data.
   
   
2. What were the effects of any data manipulations that you performed? Give the theoretical mathematical relationships that describe how the data was manipulated and explain their effect on the data.
   
   
3. What would have been the consequences if you had used a sampling rate much slower than the one you actually used? If you had used one much faster? Describe the effects of under-sampling a cyclic or repeating signal such as a cyclic voltammetry wave or an interferogram from FT-IR or NMR. What is this error called?
   
   
4. Suppose you had set the voltage range of the A/D board to + 10 Volts, but your largest signal was only + 0.1 Volts. The A/D board has a "12-bit resolution". What is the maximum voltage resolution (precision) of the board? What is the actual resolution of this + 0.1 Volt signal?