NONDESTRUCTIVE INSPECTION METHOD FOR CATHODES OF CATHODE-RAY TUBES Russian patent published in 1996 - IPC

FIELD: vacuum electronics. SUBSTANCE: flicker noise component is measured at fixed frequency f, current picked off cathode is set by varying positive voltage across anode with other electrodes placed at zero potential. Anode voltage is measured for each respective current, perveance is calculated, ratio of flicker-noise level for each set current to perveance is determined. Similar sequence of operations is used for planar diode having cathode of same type. Measurements are made at same cathode current density jCd. Cathode quality factor C_q(f,j C_cp) is found for each value of this current. Several cathodes under inspection are subjected to life test. Test results are used to determine degree of cathode current decay; combination of maximum quality factors C_q(f,j C_cp) max of cathode is found for maximum set value of such decay. Rejection is made by comparing quality factors; cathodes considered serviceable are those where following conditions are satisfied simultaneously: . Device under test is inserted in circuit affording flow of DC current picked off cathode and passed to anode. Cathode current noise builds up noise voltage across it amplified by amplifier and applied to filter. Output instrument readings are converted to spectral density values. EFFECT: improved validity of inspection results and facilitated procedure. 5 dwg