A New High-tension Voltmeter for the Direct Measurement of Tube Voltage During Diagnosis and Therapy

Abstract

Direct measurement of the voltage delivered to an X-ray tube, without reference to the form of the voltage curve, has, up to now, been impossible in practical X-ray diagnosis, and in therapy it has only been possible by very inconvenient methods, which have been applied more or less for purposes of control only. Reliance has generally been placed on the makers' standard calibration curves, which indicate the peak or the effective voltage applied to the tube with different currents by derivation from the voltage applied to the primary. This voltage can be read from a voltmeter included in the switch table, or the table voltmeter can be calibrated directly in kilovolts. The disadvantages of this method are generally known. It can be used directly only with therapy apparatus, since the voltage indicated as being applied to the primary must be effective throughout the load. In diagnostic work the loss through the windings must be taken into consideration, and this cannot be read by direct means in short exposures. Moreover, the voltage indicated by the voltmeter for the primary represents the effective mean value of the primary voltage, which is differentiated from the peak value by the amplitude factor and from the secondary voltage of the high-tension transformer by the transformation ratio and the loss of voltage in transformation. The amplitude factor is not constant in X-ray work but depends on certain variables; for example, the characteristics of the tube.