| 摘要 |
PURPOSE:To simplify the circuit by applying sequentially a voltage given to each three-phase line based on the zero phase detected for each line voltage while applying limitation to the direction so as to prevent overshoot due to transient phenomenon and eliminating the adjusting position. CONSTITUTION:Each line voltage of U-V-W-U is detected by photocouplers 1PC 3PC as an isolated signal and a zero phase timing pulse is formed by a zero phase detection storage circuit 3. When a signal (a) among zero phase timing signals (a)-(f) at a phase of high voltage is given to a gate of a thyristor 1SCR, it is conductive, the anode goes to an L potential, all signal input/output terminals B-F go to L potential, no signals (b)-(f) are generated and only the signal (a) is generated. Thus, the signals (a)-(f) are ORed by an OR gate circuit OR, only the signal (a) appears as the zero phase timing signal of the high voltage applied phase being an input of an image pickup timer circuit 5 and an image pickup switching signal XST is given to the circuit 5 synchronously with the signal (a). |
