| 摘要 |
PURPOSE:To improve detection accuracy of discharge extinction by detecting change in the ratio of values of current which flowing on two lines which connect a high frequency power source and an electrode of a discharge tube. CONSTITUTION:A current value of lines 3a, 3b which connect a high frequency power source 2 and electrodes 4a, 4b of a discharge tube 4 is measured by current measuring circuits 6a, 5b and measured values Ai, Bi are input to an operation device 6 and a current rate operating circuit 8. The operating device 6 compares set values Ri of an output set circuit 7 with Ai to control a dc power source 1. A circuit 8 operates a ratio K of measured values Ai, Bi. The ratio K is nearly 1 during discharge; however, it increased because of a stray capacity C when discharge is extinguished. Therefore, when a ratio K is larger than a set value Kr stored in a memory 9 as compared by a comparison circuit 10, an alarm signal CSa is output to stop operation of the power source 1. Thereby, it is possible to improve detection accuracy of discharge extinction and to prevent breakdown of a high frequency power source. |
