. The Röntgen rays in medical work . of output canbe easily effected in other ways, either by the use of seriesresistances to control the current, or by transformers to controlthe pressure, A form of the mercury jet interrupter is made for use on alternatecurrent circuits. It resembles the pattern used on direct circuits,except that the motor drivingit must be a synchronousmotor keeping step with thealternations. Fig. 46 shows itsappearance, and the wheelseen in the illustration is ahand-wheel, which is used tospeed up the interrupter. Such amanoeuvre is usually necessary withsynchronous motor
. The Röntgen rays in medical work . of output canbe easily effected in other ways, either by the use of seriesresistances to control the current, or by transformers to controlthe pressure, A form of the mercury jet interrupter is made for use on alternatecurrent circuits. It resembles the pattern used on direct circuits,except that the motor drivingit must be a synchronousmotor keeping step with thealternations. Fig. 46 shows itsappearance, and the wheelseen in the illustration is ahand-wheel, which is used tospeed up the interrupter. Such amanoeuvre is usually necessary withsynchronous motors, as they aregenerally unable to start from rest,and must be artificially assisted toreach their proper speed, thoughwhen once in step they maintain aconstant rate even under tryingvariations of their load. Another method of adapting thealternating current mains for theoperation of coils in axray workis to use the aluminium rectifier described in the preceding chapterin one of its four-celled forms. Though the current given out by. Fig. 46.—Turbine Break,Synchronous Motor. 78 THE RONTGEN RAYS IN MEDICAL WORK this appliance is pulsatory rather than continuous, it has been ofgreat value in the solution of the problem of the use of the alternat-ing mains. A Pollak or a Nodon valve rectifier may be used as asource of current for x-ray work, both for driving a direct currentmotor to actuate the interrupter and for supplying the primarycircuit of the coil. The rectified current may be regarded for x-raypurposes as the approximate equivalent of direct current, and thedetails laid down in the sections on direct currrent mains may beconsidered as applying equally well for all practical purposes to therectified current of either of those valves. The tendency of the Wehnelt interrupter to keep step with thepulsations of an alternate current points out another method ofmaking use of the alternating mains. The form already describedas the G-aiffe-Gallot interrupter (Fig. 29) works well
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