Data Processing

With the AU command WR the data can be written to a local hard disk. By default it will be stored in the folder 7NMR/DATA/; for details please consult the appendix . The data files consist of a header with three parts and the raw data as it comes from the scope card. The first part of the header contains the parameters such as TAU as they were set at the time of the measurement. The second part contains the time and date when the measurement started and ended. And the third part finally contains the user- and program-defined variables which start with an underscore, such as the field _B0_KG.

It is true that the AU language offers some commands which help to evaluate the integral of an echo, but we did not make use of it. It would have been advantageous if we wanted to observe a measurement. But above all it took too much time to calculate the integrals during the run causing the measurements to become too slow. On the other hand we had the occasion to process the data very conveniently with Matlab. That was the reason why we decided to write some little data processing tools, mainly some Matlab scripts that import the data from the SeveNMR output files (import <fileXXX.dat> or import <file> <number>) and four integrators for all of our types of measurements: the frequency sweeps, the field sweeps, T₁ and T₂ measurements.

After the integration the result is stored in a Matlab matrix, plotted and printed to the screen in a tabular form. Then we store these tabulations to the NMR server, a file server which is running on the old measurement computer. The system it runs with is the freely available Linux distribution RedHat 6.0. The data stored in that computer is available from every other computer in the internet, but the access to it is locked with passwords. The further data processing is done with ProFit 5.1.2, for which we have to change to an Apple computer. Owing to the NMR server we don't have to carry the data on discs anymore, which helps -- in the presence of the high magnetic fields in our laboratory -- to save discs and nerves. In ProFit we finally do what has been done since years; I think there is no need to explain the procedure of fitting and plotting the data. We don't want to show any code in this section. But you can find the programs in D: nmrtools matlab . They should be well commented.