Light measuring apparatus
AssigneeCopal Company Limited
InventorMasaru Yamazaki
Life of this patent
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Abstract
A light measuring apparatus comprising a photoelectric element exposed to incident light and coupled to a plurality of parallel-connected capacitors which integrate the photoelectric current output from the element. Control means successively switch each of the capacitors in parallel as the photoelectric current charges a first previously switched capacitors in accordance with the voltage integrated on the capacitors as sensed by a comparator. After a predetermined time, the parallel charged capacitors are discharged through a constant current source, with the discharge time being digitally monitored to produce a digital output proportional to the incident light level.
Claims8
A light measuring apparatus for measuring the intensity of incident light, comprising:
- photoelectric means coupled to said light for generating photoelectric current in dependence on the intensity of said incident light;
- capacitor integrating means coupled to said photoelectric means for integrating for a predetermined time period the photoelectric current so as to produce an integrated electric charge in said capacitor integrating means which is proportional to the total quantity of said light incident to said photoelectric means for said predetermined time period;
- a constant current source capable of generating current of at least one constant current level;
- control means coupled to said capacitor integrator means and said constant current source for controlling the discharging/charging of the electric charge of said capacitor integrating means through said constant current circuit so as to vary the voltage of said capacitor integrating means;
- said capacitor integrating means comprising a plurality of parallel connectable capacitors adapted to be successively connected in parallel to the previously connected capacitor under the control of said control means, and
- said control means comprising,
- shift register means coupled to each of said capacitors for controlling the charging/discharging of each of said capacitors,
- comparator means coupled to said capacitors and said shift register means for actuating said shift register means to connect a respective succeeding capacitor additionally in parallel to the previously connected capacitor each time the voltage of the respective previously parallel connected capacitors reaches a predetermined comparison voltage applied to said comparator means, and
- means for applying said predetermined comparison voltage to said comparator means.
Dependencies are inferred from the claim text.