| 摘要 |
PURPOSE:To enable life to be predicted by setting a target threshold of life and by calculating filament current ratio from the detection filament current and setting initial value. CONSTITUTION:A filament current Ii and an integral value Ti of current- conduction time for the filament are measured at a filament current detection part 14 and by a total current-conduction time 16, respectively. Also, an initial value Imax of filament current and target threshold Rsh of life are set previously at a setting part 18. Then, a filament current ratio calculation part 20 calculates a filament current ratio Ri from the current Ii and the initial value Imax. Then, an operation part 24 determines time ratio corresponding to a current ratio Ri according to a characteristic curve and the current ratio Ri of change with time of filament current which are stored in a memory 22. Then, remaining time required before the current ratio Ri reaches the threshold Rsh is calculated from this time ratio and the integral time value Ti, thus enabling filament life to be predicted. |
