File:X-ray manual - U.S. Army (1917) (14570650388).jpg

Identifier: xraymanualusarmy00unit (find matches)
Title: X-ray manual : U.S. Army
Year: 1917 (1910s)
Authors: United States. Surgeon-General's Office American Roentgen Ray Society
Subjects: X-rays Fractures Teeth Chest Heart Radiography
Publisher: New York : Middleditch
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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e very much smaller than that giving direct. Valve Tubes. In order to reduce inverse as far as possible, variousunsymmetrical tubes, Fig. 17, have been devised; theseoffer much greater resistance to discharge in one direc-tion than the other. Such valve tubes are often supple-mented by a series of small spark gaps which are readilybroken down by the direct. but not by the lower volt-tage inverse. These devices all reduce the energyavailable for Roentgen ray production. Fig. 18 shows atube designed to indicate the presence of inverse. Ifthere is no inverse, only one of the metal terminals atthe gap will glow. If both glow to the same extent, theinverse current is present. Fig. 19 shows the wiring diagram for a coil with mer-cury interrupter, condenser, oscilloscope, valve tube, andseries spark gap. Note that the milliammeter is next tothe tube. When the spark gap is placed between the meter andthe tube, leakage across the gap may make the readingmuch above that passed through the tube.
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;NIIMM;!lll;IIIHv imniimiMililil/ Fig. 17. Valve Tube. *€ A. ^ Fig. 18. Vacuum tube oscilloscope. 48 X-RAY MANUAL—U. S. ARMY Interrupters. The secondary voltage of an induction coil is theresult of change of current in the primary. It is evidentthat we cannot have the primary current grow indefin-itely, so we must allow it to decrease and increasealternately. The value of the secondary voltage for agiven coil depends entirely on the rate at which the pri-mary current is changed. Thus, if a current of 80amperes should be reduced to 0 amperes in .02 seconds,the current has changed at a mean rate of 4000 amperesper second. If it required .04 seconds for the samechange, the rate is 2000 amperes per second. The meansecondary voltage is twice as great in the former caseas in the latter. As induction coils are usually operated on an inter-rupted direct current, some device must be used to openand close the circuit. The early interrupters were ofthe vibrating hammer type, but these have l

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