Automatic light intensity control for x-ray film viewer

Details Automatic light intensity control for x-ray film viewer Automatic light intensity control for x-ray film viewer

1976-11-29

1978-10-03

LaRoche, Eugene R.

Card, picture, or sign exhibiting

Photographic transparency viewer, e.g., x-ray viewer

250205, 315158, 315194, 315151, H05B 3702

Patent

active

041186540

ABSTRACT:
The intensity of light penetrating an X-ray film being viewed is automatically maintained at a preset, adjustable, eye comfort level. A photosensor detects the average light level on the observer side, and its output controls the charging time of a capacitor coupled to the emitter of a unijunction transistor. When the capacitor reaches a predetermined voltage it fires the transistor and dumps its charge through a pulse generator which in turn triggers a gated semiconductor connected in series with the viewer light source. The period between successive firing cycles is proportional to the penetrating light level. Thus, if the light level increases, as when a relatively transparent film negative is inserted in the viewer or when a negative is removed, the capacitor charging time increases, the firing period increases, and the light source intensity therefore decreases to restore the preset level of light penetration.

REFERENCES:
patent: 3473084 (1969-10-01), Dodge
patent: 3796916 (1974-03-01), DeBelder
patent: 3952242 (1976-04-01), Ukai

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