Apparatus for and method of measuring beam spot luminescence distribution

Claim 1

A measuring device wherein a luminescence distribution within a beam spot of an electron beam irradiating a tube surface of a color cathode ray tube is measured, said measuring device comprising: an electron beam moving means for varying locations irradiated by the electron beam while maintaining a measurement region of brightness defined within a specific fluorescent substance on said tube surface within the beam spot, said electron beam moving means including a synchronous signal phase control device for varying phases of synchronous signals provided to a deflecting circuit of the cathode ray tube, and a control circuit for supplying said synchronous signal phase control device with a command signal in response to a phase amount corresponding to each irradiated location of the electron beam; and means for measuring the brightness of said measurement region at each irradiated position of the electron beam wherein said synchronous signal phase control device comprises: means for shifting a phase of a reference horizontal synchronous signal in response to a first command signal from the control circuit, and means for shifting a phase of a reference vertical synchronous signal in response to a second command signal from the control circuit wherein said means for shifting the phase of the reference horizontal signal comprises: a delay line for shifting a phase of the reference horizontal synchronous signal by a prescribed quantity and generating a plurality of delayed horizontal synchronous signals, and a selector for selecting one delayed synchronous signal in response to the first command signal, and wherein said means for shifting a phase of the reference vertical synchronous signal comprises: a first counter for starting counting from a rising edge of the reference vertical synchronous signal and for counting reference pulses corresponding to a first phase deviation quantity indicated by the second command signal, a second counter for starting counting from a falling edge of the reference vertical synchronous signal and for counting reference pulses corresponding to a second phase deviation quantity, and a flip-flop set by an output of said first counter and reset by an output of said second counter.