Physics, Techniques and ProceduresBattery-powered generator
a mobile
X ray generator running on large capacity nickel-cadmium batteries. The batteries are charged by the standard power supply. The charging may take 12 hours. After charging, the generator may be used without connection to any power supply. This heavy unit may store 10 000 mAs. Unlike the mobile
capacitor discharge generator, the voltage (kV) is kept constant during exposures.
To achieve high voltage for the X ray tube, the direct current (DC) from the batteries are fed to a "chopper" which "chops" or interrupts the DC about 500 times per second, yielding a 500-Hz pulsed DC. The high frequency is advantageous because the output voltage produced in a transformer is proportional to the frequency of the input current (see medium frequency generator). This high-frequency DC supplies the primary windings of a transformer which produces a high-voltage alternating current (AC) with the same frequency (500 Hz). After rectification, the AC is transformed into a 1 000-pulse per second DC (both the positive and negative part of the AC waveform give a forward pulse), and this high-voltage, high-frequency DC is smoothed giving a nearly constant potential DC which is supplied to the X-ray tube.
HJS