The Data Acquisition System of the DIMM with Three-subaperture

The Differential Image Motion Monitor with three sub-aperture (DIMM) was developed at Yunnan Observatory. The data acquisition system of the DIMM consists of a MTV1881C CCD camera with its sensor fixed at the focal plane, a CA6300 image process board for grabbing pictures sent from camera, a TV set which shows the data images in the CA 6300 and a IBM 386 PC which controls the whole system. The frame of the CCD is 795×596, and the size of each pixel is 10×10.2μm. When working at the image viewing mode, 512×512 frame is useds when working at the data acquisition mode, only 64 ×64 programmable target window is used, and each pixel is digitized to shits resolution. The exposure time is 40ms, framerate is 25f/s or 12.5f/s, and 512 frames are grabbed each time to comprise a data sequence. The computer controls the whole system, performs all the calculation and saves data of images to disk. The quality of the frames is checked before data reduction, and more software is used to analyse the results