Diffractometer input and output

The automatic diffractometer, whatever its type, can be regarded as a black box which accepts numerical input information of one kind and produces numerical information of another kind. The input information consists of the settings of the various crystal and detector shafts and all the instructions necessary to make valid measurements of the intensities of Bragg reflexions. The output data consist of the results of those measurements. The generation of the input information and the processing of the diffractometer output must inevitably be carried out by means of a computer: the rate at which measurements are made by an automatic diffractometer is such as to make manual computation with a desk calculator quite impracticable.

It is important, therefore, that the input and output medium of an automatic diffractometer be one which is readily generated and read by a computer. (In the case of analogue diffractometers, discussed in §3.3, only the output medium needs to be considered.) The most common media are punched cards or punched paper tape: the choice between these two is generally dictated by the computer installation which is used in conjunction with the diffractometer. It may be noted in passing that punched cards offer a greater flexibility in that the sequence in which reflexions are to be measured and the sequence in which experimental results are listed can be varied by simply resorting a stack of cards.