RESUMO
Although the type of XHD150B-IO 800mA X-ray machine possesses a damage protection electric circuit for the main thyristors, with the first switch of photographic hand valve pressed, abnormal instant exposure still appears when double (in different phase) or more than three main thyristors are broken through, short-circuited or mis-energized, and consequently the high voltage element or X-ray machine will break down. Therefore the original electric circuit must be improved. Material: A few of leads. Method: We exchange the conjunction sequence of three NO (normal open) contacting points of radiograph high voltage preparing work relay--MAG SW- R with three reverse parallel connection of main thyristors. Conclusion: The normal procedure of radiographic exposure won't be disturbed after the improvement. When whichever one or more than two main thyristors is broken through, short-circuited or mis-energized, the spoilage can be detected instantly and the protection circuit works correspondingly, which guarantees the safety of X-ray machine.