Digital storage capacity

For some mass spectrometers, such as TOF mass spectrometers, for reasons of data transfer speed and data storage capacity, the data acquisition system needs to accumulate data for a period of time in the summing memory, and forward the accumulated data to the data system. Each spectrum is added to the sum of the previous spectra so that a continuous summation process takes place. This type of data acquisition system is called digital signal averaging (DSA) or integrating transient recorder (ITR). Figure 3.8 illustrates the principle of mass spectrum acquisition with this type of system. 

Concomitant with the increased data size, the memory requirements for permanent storage will render It necessary to expand the storage capacity of backup stores. Disk storage capacities of over 100 M-byte, as they have become available in the form for example of the CDC 9730 Series, are a true necessity in many hlgh-fleld NMR applications. Memory requirements are particularly severe in two-dimensional spectroscopy such as the 2D-J experiments where spectral arrays are obtained In which spin-spin coupling Is separated from chemical shielding. A 10 ppm x 50 Hz 2D spectrum with a digital resolution of 2 Hz on the axis and 0.2 Hz on the J axis, for example, corresponds to a 4 M-word data matrix. 

Special equipment for transient and impedance measurements consists of a digital storage oscilloscope and a frequency response analyzo. A suitable oscilloscop>e should have at least two channels with 1 kB (1024 measurement points) storage capacity. A frequency response analyzer is usually a complete unit which can produce the excitation signal, make naeasurements, process and analyze the measurement data. 

Because of the elaborate calculations and data processing required for this kind of mathematical analysis, it has not been feasible to consider potentially useful techniques to accomplish this task manually. However, with the recent availability of high-speed digital computers of large storage capacity, and the development of data-handling techniques, such an extensive lipoprotein analysis becomes not only entirely realistic, but perhaps necessary in order to increase our understanding of the human lipoprotein system. 

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