| 摘要 |
PURPOSE:To prevent the insulation breakdown of an x-ray tube reliably by providing a switching device to vary the limited voltage on x-ray tube voltage limiting elements connected in parallel to the x-ray tube to limit the applied voltage to the x-ray tube. CONSTITUTION:A switching device 19 is provided with three switching contacts A-C to be connected to a connection terminal which is connected to the switching contact B in the standard state. When the terminal is connected to the contact A, three elements of unit varistors 24 are short circuited to decreased the number of elements connected in series. In this case the total limited voltage shifts to the decreasing direction, thus the limited voltage can be lowered. That is, when the limited voltages of unit varistors 24 are fluctuated in higher direction, by short circuiting a number of element of the unit varistors 24 as above, the total limited voltage can be lowered by a voltage corresponding to the limited voltages of the short circuited unit varistors 24. When the connection terminal is connected to the switching contact C, the total limited voltage shifts to the increasing direction, so that the limited voltage by zinc oxide varistor 17 can be elevated. |
