Phototiming control method and apparatus

Abstract

An improved phototimer control and compensation scheme is provided. The control monitors electrical signals produced by a plurality of photomultiplier tubes. PMT dark current is sampled prior to exposure and is compensated for as exposure begins. Each PMT produces a signal proportional to incident radiation which is integrated by separate integrator means to produce first ramp signals. Switching means are provided for selecting any one or combination of first ramp signals. Mixing means combines selected first ramp signals. Amplifier means amplifies mixed signals as a function signals selected to produce a second ramp signal. Gain selection means compensates the gain of the second ramp signal to the speed with the film-screen combination chosen. An exposure compensation scheme produces an exposure reference signal defining the net effect of system variables. Equations defining kV reference curves are stored in a first storage means. Digital data values representing characteristics of different film-screen combination are stored in a second storage means. A processor develops a kV ramp reference signal base on one of the kV reference curves and data values. Scaling factor equations and values representative of system variable are also stored in the first and second storage means. The processor includes means for developing scaling factor which compensate the reference signal for the effect of system variables on film density.