| 摘要 |
PURPOSE:To be able to take measures such as suspension of photographing or resumption of it in an early stage, by comparing an output signal from a detection means with a reference value and providing a notifying means to an operator in the case where the difference in the above exceeds a limiting value. CONSTITUTION:It is presumed that a filament is broken at a time t1 and after that intensity of electron beams becomes about zero. As a result, the difference between a signal from a sample holding circuit 11 and a signal sent to the first comparator circuit 12 through an amplifier 10 exceeds a preset limiting value at a time t2, so that the output signal of the first comparator circuit 12 is changed to a high level signal from a low level signal and an output signal of the second comparator circuit 17 is changed to a low level from a high level, after a time t3. Therefore, when the time t2 is prior to the time t3, the output signal of AND circuit 13 is also changed to a high level at the moment when the output signal of the first comparator circuit is changed to a high level. Thus, a lamp driving circuit 20 lights a lamp 19 at the receipt of this high level output of the AND circuit 13 and notifies and operator that the photographing ha ended in failure.
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