Signal digitization

When modern NMR was in its infanq, few if any scientists realized that they would ever require a two-coil NMR probe in which the coil lies inside the broadband coU. It was not until the demonstration that experiment time can be drastically reduced for the acquisition of 2-D heteronuclear correlation NMR data sets by employing H detected methods and a two-coil NMR probe with the coil configurations inverted (relative to the normal coil configuration described above) that the inverse probe really caught on. Now the inverse probe (a probe with the coil closer to the sample than the broadband coil) is a staple in nearly every modern NMR laboratory. 

An electronic device that converts an analog voltage into a binary number composed of discreet digits (a series of I s and O s). 

Digitization. The conversion of an analog voltage to a digital, binary number amenable to subseguent computational manipulation. 

Sweep width, SW. The amount of the frequency spectrum spanned, which Is controlled by the dwell time. (Note that spectral window Is not the same thing but Is also denoted SW— a great source of confusion). 

Dwell time. The time Interval between sampling events for the digitization of the analog signal arising from the FID equal to the reciprocal of the sampling rate. 

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The ion detection system consists of a high-gain electron multiplier and the signal digitizing system, along with a computer for data acquisition and manipulation. 

In summary, the Fourier transform of a continuous signal digitized in 2A/ + 1 data points returns N real Fourier coefficients, N imaginary Fourier coefficients and the average signal, also called the DC term, i.e. in total 2N + 1 points. The relationship between the scales in both domains is shown in Fig. 40.9. 

Rabiner, 1982] Rabiner, L. R. (1982). Digital techniques for changing the sampling rate of a signal. Digital Audio collected papers from the AES premier conference, pages 79-89. 

Highly sensitive detectors, coupled with the facility to store each absorption signal digitally for each separate analysis time in a microcomputer, have enabled absorbance changes as small as 0.001 to be accurately measured. 

The spectral region of interest is then detected and processed by means of an optical multichannel analyzer (EG G-PARC model 1215, OMA). The OMA detector SIT (silicon intensified target), EG G-PARC model 1254 has been used. It is operated by the detector controller, EG G-PARC, model 1216, which performs the signal digitization as well. The acquired spectra are displayed in real time on a TV display and on the OMA console. The data storage and processing are also performed by that console which has a 28K of 16 bit core memory and a floppy disk for permanent storage. 

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