The current sent from an induction-coil through an X-ray  tube consists of a rapidly recurring series of brief currents  induced in the secondary circuit in consonance with the  interruptions of the current sent to the coil from the inter-  rupter or break. This secondary current will depend initially  upon the strength of the primary current employed; further,  upon the rate of interruptions of that current; and, as regards  the coil, mainly upon the relative lengths of the primary and  secondary windings thereon. It may be recalled that this  inductive effect is due to the interruptions of the primary  current. The suddenness of those individual interruptions,  as well as the duration of actual passage of current in the  intervals, will affect the character of the secondary current  induced. As already noted, the break in the current produced  by the interrupter must be as sharp and sudden as it can  possibly be made.

At each ‘make’ of the primary current a momentary  current is induced in the secondary circuit in a direction  opposite or ‘ inverse’ to that in the primary, and at each  ‘ break’ there is induced a momentary ‘ direct’ current of  greater power. Those direct currents at break are alone  desired in the discharge of the coil for X-ray purposes, the  inverse currents, as mentioned earlier, being of damaging  effect. The actual E.M.F.’s of the two induced currents are  equal; but the current at ‘ make ‘ is more slowly induced, and  this delay is increased by nse of a condenser, while at’ break’  the secondary current is induced much more sharply. Thus  the currents at break may be said to be in quality more  ‘ impetuous/ and manifest themselves as sparks; while those  at make are more ‘ deliberate,’ and fail to form sparks under  ordinary circumstances. Where the potential of the primary  current exceeds 50 volts, however, the effect of these ‘ make’  or inverse currents becomes noticeable in the fluorescence of  the X-ray tube. This effect is marked by a flickering, greenish  fluorescence in the hemisphere of the tube ordinarily free  from illumination.

No related posts.