Abstract: An x-ray tube mA regulator has an SCR phase shift voltage regulator supplying the primary winding of a transformer whose secondary is coupled to the x-ray tube filament. Prior to initiation of an x-ray exposure, the filament is preheated to a temperature corresponding substantially to the electron emissivity needed for obtaining the desired tube mA during an exposure. During the preexposure interval, the phase shift regulator is controlled by a signal corresponding to the sum of signals representative of the voltage applied to the filament transformer, the desired filament voltage and the space charge compensation needed for the selected x-ray tube anode to cathode voltage. When an exposure is initiated, control of the voltage regulator is switched to a circuit that responds to the tube current by controlling the amount of phase shift and, hence, the voltage supplied to the transformer.

Abstract: Signals associated with heart beats occurring at the normal rhythm of the heart and also with extrasystoles or PVCs are fed to a one-shot multivibrator which is enabled to produce clock signals corresponding with incoming heart activity indicating signals such as R-wave signals provided the R-wave signals are spaced in time to correspond with normal heart rhythm. An analog signal corresponding with average heart rate is fed to an integrator. The ramp output of the integrator is fed to one input of a comparator and a reference signal representative of a percentage of time between normal rhythm R-waves is fed to the other input of the comparator. Until the two input signals cross over, the output signal of the comparator is such as to inhibit output of a clock signal from the multivibrator so R-wave signals associated with extrasystoles occurring during the integration or lockout period are not gated through the multivibrator.