. Elementary and dental radiography / by Howard Riley Raper . sent through the X-ray X-Ray machines. tube, obviously this governs to a great extent the time of exposure necessary. Taking into account the machines of all MAKING DENTAL RADIOGRAPHS 125 sizes which are in general use the time of exposure necessary with IN-DUCTION COILS, for intra-oral dental radiographs, varies from a frac-tion of a second to about 15 or 20 seconds, for extra-oral dental radio-graphs, from about 1 or 2 seconds to about 45 seconds; with HIGH-FREQUENCY COILS, for intra-oral dental radiographs, from about3 to 30 seco
. Elementary and dental radiography / by Howard Riley Raper . sent through the X-ray X-Ray machines. tube, obviously this governs to a great extent the time of exposure necessary. Taking into account the machines of all MAKING DENTAL RADIOGRAPHS 125 sizes which are in general use the time of exposure necessary with IN-DUCTION COILS, for intra-oral dental radiographs, varies from a frac-tion of a second to about 15 or 20 seconds, for extra-oral dental radio-graphs, from about 1 or 2 seconds to about 45 seconds; with HIGH-FREQUENCY COILS, for intra-oral dental radiographs, from about3 to 30 seconds, for extra-oral dental radiographs, from about 12 secondsto about 1 minute; with TRANSFORMERS, for intra-oral dental radio-graphs, from a fraction of a second to about 5 seconds, for extra-oraldental radiographs, from a fraction of a second to about 10 seconds. INDUCTION COILS, of various sizes operating at their fullcapacity, are capable of forcing from 4 or 5 to about 18 -f- milliamperesthrough a tube backing up 5 or 6 inches of parallel spark; HIGH-. Fig. 115. Lead-lined, X-ray-proof box for photographic supplies. FREQUENCY COILS from about 3 to about 8 milliamperes; TRANS-FORMERS from about 12 to about 60 -)- milliamperes. (The plus markplaced after milliamperage 18 for induction coils and 60 for transformersis put there in recognition of exceptional X-ray machines of these typeswhich are capable of delivering a higher milliamperage. As I say, how-ever, these largest machines are exceptional, , not the type of machinecommonly met with.) Ordinary X-ray tubes, gas tubes, as they are calledsince the advent of the new Coolidge tube, could not take a current of60 milliamperes for much longer than about 1 second continuously with-out injury to the tube from overheating. When the time of exposure is over 5 seconds it is best to make theexposure intermittently: turn the current on for 5 seconds then off for 5seconds, then on for 5 seconds and so on until the desired time of
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