| 摘要 |
PURPOSE:To detect a vertical position deviation by superimposing a position detecting pulse on a video signal and obtaining the timewise deviation of an output of the pulse signal by means of a photodetector referencing a cathode ray tube at a normal horizontal position. CONSTITUTION:Pulse signals S1-S3 for detecting position comprising plural pulses having nearly identical horizontal position at the horizontal blanking period are superimposed on a color video signal inputted from terminals t1-t3 and outputted from cathode tray tubes CRT1-CRT3. When the picture image by the cathode ray tube CRT2 is shifted downward and the picture image by the cathode ray tube CRT3 is shifted upward respectively, output signals S2'', S3'' of photodetectors PR2, PR3 are outputted by taking a time delayed by DELTAT2 and advanced by DELTAT3 respectively from the normal times T1, T2 extending from a vertical synchronizing signal VSYNC up to the center of the signals S1, S3 as a center. The DELTAT2 and DELTAT3 are timewise deviations representing the degree of vertical shift of the video image by the cathode ray tubes CRT2 and CRT3. |
