X-ray tube emission current controller

Digital values representing trial bias voltages that are to be applied to the control grid of an x-ray tube are stored at respective locations in a battery energized RAM. The addresses of the locations correspond to the nominal x-ray tube currents that relate to the bias voltages. A model of the actual bias voltages for selected tube currents is made and supplants the trial voltages. A trial digital bias value is converted to an analog signal used to control the output level of a generator that applies the bias voltage to the grid. An x-ray exposure is made. The x-ray dosage in terms of actual milliampere-seconds (mAS) is measured and compared with a reference desired mAS value. A computer calculates to a first approximation the bias voltage that should have been applied to obtain the desired mAS and returns the new digital bias voltage value to the same location. The process is repeated for each of a range of tube currents until actual and desired mAS agree at which time the corrected bias voltages are stored. When later the x-ray system is used for patient exposures, operator selection of tube mA level brings about automatic application of the proper bias voltage for the particular tube.