The selected subject gives a general design of the grating auto testing instrument, by using the characteristics of orthogonal A and B signals output by optical encoder and symmetrical black and white linear transmission grating bar, and analyzing the means of the high electrical level of signals change to number of counter pluses. Then, the key technologies in the realization of the grating auto testing instrument are introduced particularly. In the design, we select the HEDS-9730Q optical encoder of Agile...