Method for reticon signal processing in the Lower Latitude Meridian Circle (LLMC)

The functions and characteristics of the 1(st) to 9(th) Reticon signals used to measure positions of reticle/slit images in the LLMC are described in this paper. According to their characteristics, we present a new method to process these Reticon signals, which consists of a filtering algorithm and a centering algorithm. The filtering algorithm is developed to process the 5(th) to 9(th) Reticon signals, because in these signals there are obvious disturbance components caused by the backaround light in the microscopes. An auto-estimating technique is developed to estimate and eliminate the disturbance signal of the background light by a piecewise-linear fitting. The centering algorithm is used to determine the positions of all the reticle/slit images in 3 steps. The first is to search all the wave crests and troughs of a Reticon signal, the next is to determine a threshold for each wave and then to center the wave by a modified moment method so as to get the position of the reticle/slit image, and the last step is to average all the position data of the waves in a Reticon signal to get an integrate position data of a group of reticles/slits in the corresponding reading microscope, The technique of implementation of the method in C++ programming language is also described in the paper.