A CONVERGENCE MEASUREMENT APPARATUS FOR A COLOUR CRT (1) COMPRISES A LIGHT SENSOR (4) WHICH IS PLACED ON THE SCREEN (2) OF THE CRT (1) TO BE TESTED, A CPU (8), AND A PATTERN GENERATOR (15) WHICH CAUSES A PLURALITY OF LUMINESENCENT LINES OF A PRIMARY COLOUR TO BE DISPLAYED ON ONE AREA (S1) OF THE SCREEN (2) AND A PLANE AREA WHICH IS A COMPOSITE OF THE TWO OTHER PRIMARY COLOUR TO BE DISPLAYED ON ANOTHER AREA (S2) OF THE SCREEN. THE LINES ARE SHIFTED AT A GIVEN RATE ALONG THE DESIGNATED AREA (S1) OF THE SCREEN (2), THE COLOUR OF THE DISPLAYED LINES SUCCESSIVELY CHANGING TO EACH PRIMARY COLOUR. THE LIGHT SENSOR (4) RECEIVES LIGHT INTENSITY INFROMATION FROM THE GENERATED PATTERN AND THE CPU (8) CALCULATES A MIS-CONVERGENCE VALUE BASED ON THE LIGHT INTENSITY DATA. THE APPARATUS FURTHER INCLUDES A SELF-INSPECTION FEATURE BY WHICH THE PROCESSING IS EXECUTED FOR SUCCESSIVE MEASUREMENTS OF THE SAME PRIMARY COLOUR. IF THE VALUES FOR EACH MEASUREMENT ARE IDENTICAL, THE SYSTEM IS ASSUMED TO BE OPERATING NORMALLY, BUT IF THERE IS VARIATION, ABNORMAL OPERATION CAN BE DIANOSED.(FIG 1,7)
CONVERGENCE MEASUREMENT APPARATUS FOR COLOUR CATHODE RAY TUBES.