. The Dental cosmos. r (Fig. 3, a). Thisdesignates, by the use of numerals, tin1resistance in the secondary circuit. Theresistance in the secondary circuit isgoverned very largely by the resistancein the X-ray tube, which, in turn, isdependent upon the degree of vacuumwithin the tube. A high or rare vacuumwill produce rays of great penetrationand also cause a high resistance. Con-versely, a low vacuum will cause lessresistance and produce sofl rays. Ob-viously, therefore, if the qualimeter reg-isters S, 9 or 10, the resistance is high,and presumably the rays obtained arc1bard in quality. It mu
. The Dental cosmos. r (Fig. 3, a). Thisdesignates, by the use of numerals, tin1resistance in the secondary circuit. Theresistance in the secondary circuit isgoverned very largely by the resistancein the X-ray tube, which, in turn, isdependent upon the degree of vacuumwithin the tube. A high or rare vacuumwill produce rays of great penetrationand also cause a high resistance. Con-versely, a low vacuum will cause lessresistance and produce sofl rays. Ob-viously, therefore, if the qualimeter reg-isters S, 9 or 10, the resistance is high,and presumably the rays obtained arc1bard in quality. It must be mentioned,however, thai every tube is a law untoitself in Ibis respect. We have seen tubes causing a high resistance1 give offsoft rays, and rice versa. It is thereforeessential that each tube be thoroughlytested before it is used for practical pur-poses. Again, the resistance and conse-quently the qualimeter reading, will varywith the amount of current brings us to a consideration of the Fig, Radiograph of Benoist 5 degrees of hardness. estimation of the amount of current used. The milliamperemeter is used for thispurpose (Fig. 3, b). This, of course, isan instrument with which everyone ismore Or less familiar, and which requiresno special description. It is connectedwith, and registers, the amount of cur-rent in the secondary circuit. Tt shouldbe stated, too. that this instrument willnot register correctly when there is anyinverse current, such as is obtained whens Ruhmkorff coil is used to actuate1 thetube. Today, however, the inverse cur-rent is not a serious source of trouble, asa well-constructed valve tube (, d) will eliminate this objectionablefeature when a coil is employed, andwith the newer types of exciting appa-ratus, such as the interrupterless trans-former, there is no inverse current toe(ipo with. \ow as to the practical use of these
Size: 1450px × 1722px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookiddent, booksubjectdentistry
