| 摘要 |
A solenoid comprises two coils wound on a common axis and a core within the coils which is supported for movement along the axis. Direct currents are applied substantially continuously to the two coils for resistively heating the solenoid to a temperature substantially above the ambient temperature. The direct currents are applied in the same direction to the two coils to produce additive magnetomotive forces when it is desired to energize the solenoid and in opposite directions to the two coils to produce subtractive magnetomotive forces which tend to cancel, when it is desired that the solenoid be in its unenergized condition.
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