| 摘要 |
A radiation measuring device for ultra-violet, visible or infra-red radiation, particularly suitable for use in a color analyser for photographic printing has a photomultiplier tube with a current sensing resistor in the anode circuit. The voltage across this resistor is used to control the amplitude of oscillation of an oscillator which, via a step-up transformer and rectifier circuit, provides E.H.T. for the tube. The E.H.T. voltage is thus controlled to maintain the anode current sensibly constant. The controlled E.H.T. voltage also is applied to the bleeder resistor chain for the dynodes of the photomultiplier tube, which resistor chain, with a series measuring resistor, forms a potential divider; the voltage across the measuring resistor is proportional to the logarithm of the light intensity and a temperature compensated correction circuit is provided to improve the linearity of this relationship. The voltage across the measuring resistor is applied to one input of a differential voltage measuring circuit having, in the case of a color analyzer, a second input from potential sources switched in synchronism with the color filter selection.
|
