| 摘要 |
PURPOSE: To make a device low cost by dispensing with a signal source for detecting a cathode current and also to perform the correction made to correspond to a secular change at high accuracy by detecting the cathode current at high accuracy. CONSTITUTION: A controller 109 is provided in this device 100 and when the controller 109 becomes a forced adjustment mode, it outputs a control signal S109a to a video amplifier 101 in a vertical period to make the amplifier 101 output a signal in which the video signal is not present at it output regardless of the input of the video signal and in which a pedestal level is a black level and an average cathode current at this time is detected. Next, the controller outputs a control signal S109b to the amplifier 101 to make the amplifier output a signal whose state is a gray color as a luminance level and an averaged cathode current at this time is detected. Then, the control calculates the difference between both cathode currents and compares the measurement value with an initialiset value and it outputs a control signal S109B to the third terminal T3 of a cut-off control amplifier 105 so that the measurement value becomes the initialset value.
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