Large dynamic range small-angle diffractometer D22

Small-angle scattering is a technique that measures the deviation to small angles (much less than one degree to several degrees) of an X-ray or neutron beam due to structures of small size in the sample. “Small” means dimensions of a few tenths to about 100 nanometres, such as clusters in alloys, polymers, or biological macromolecules.

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Timing of real-time acquisition

Fig. 1: Scheme of real-time events

Once the real-time acquisition has been started by the MAD command KIN, the acqusition electronics gets set up by MAD for a total number of frames and for a number of subsets.

After this initialisation, the READY signal is set and maintained until the first subset has been measured. The acquisition system now waits for the TOP signal (rising TTL flank). When this is received, the first frame gets started, and the OUT ENABLE is set.

The OUT ENABLE falls at the end of the first subset, as does the READY. OUT ENABLE remains low until the TOP for the next set of frames has been received. In case of multiple subsets, the READY signal rises again as soon as the next subset is ready to be started. (The interruption is only of the order of microseconds). The acquisition system waits for a new TOP.

In the case of a single run, READY remains low until a new series is started by MAD.

The whole procedure can be repeated n times using the repeat item in the KIN command.


Web document produced by Roland May, ILL Grenoble (last update: 03-Apr-2002)