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Title: Photoelectric sensing system with light source compensating means
Claims: What is claimed is: 1. A photoelectric system for detecting interruptions of a light beam comprising means for emitting a serial train of light pulse signals constituting the light beam, means for sensing each one of the emitted light pulse signals, and means enabled by said sensing means for controlling said emitting means to modulate the duty cycle pulse width of the emitted light pulse signals to compensate for transmission variations not constituting an interruption of the light beam. 2. The photoelectric system set forth in claim 1 wherein said emitting means comprises a light emitting diode, means for generating clock pulse signals, means having two states and responsive to said generating means for defining ones of the states in accordance with the state defined at time of occurrence of each of the clock pulse signals, and means connected to said defining means and responsive to a first one of the states thereof for enabling said light emitting diode to generate a light signal. 3. The photoelectric system set forth in claim 2 wherein said sensing means comprises a photoelectric diode for detecting the generated light signals said photoelectric diode having a reverse value of resistance dependent upon the amount of illumination contained in the generated light signal. 4. The photoelectric system set forth in claim 3 wherein said controlling means comprises a capacitor connected in series with said photoelectric diode, means connected across said capacitor and responsive to a second one of the states of said defining means for establishing a discharge path for said capacitor, and means enabled by said capacitor in response to the amount of illumination contained in the detected light signal for selectively resetting said defining means to the second state to inhibit said enabling means from further generating the light signal. 5. The photoelectric system set forth in claim 4 further comprising means enabled by the second state of said defining means and by the transition between states thereof occurring at successive ones of the clock pulse signals for deriving continuous and interrupted signals indicating respectively an uninterrupted and interrupted light beam. 6. A photoelectric system for detecting interruptions of a light beam comprising means including a memory element and a clock pulse generator for emitting a serial train of light pulse signals constituting the light beam in response to clock pulse signals, means for sensing each of the emitted light pulse signals, and means responsive to the amount of illumination contained in each sensed emitted light pulse signal for controlling said memory element to modulate the duty cycle pulse width of the sensed emitted light pulse signal to compensate for short-term transmission path variations not constituting a light beam interruption. 7. A photoelectric system comprising a clock circuit for generating clock pulse signals, a memory element having two states and connected to said clock circuit for defining ones of the two states in accordance with the state defined at the time of occurrence of each of the clock pulse signals, a light emitting generator connected to said memory element and enabled by a first one of the states thereof for generating a light signal, a photoelectric sensor for detecting the generated light signal, a detector enabled by the first state of said memory and by the transition of of the states thereof occurring at successive ones of the clock pulse signals for deriving output signals indicating uninterruption and interruption of a light signal transmission path beween said light emitting generator and said photoelectric sensor, and means connected to said photoelectric sensor and said memory element for compensating for short-term variations occurring in the light signal transmission path by resetting said memory element to a second one of the states to modulate the duty cycle pulse width of the generated light signal in accordance with the amount of illumination contained in the detected light signal. 8. A photoelectric system for detecting interruptions of a light beam comprising means including a memory element and a source of clock pulse signals for emitting a serial train of light pulse signals constituting the light beam, said memory element having a clock terminal to which said clock source is connected and a reset terminal, means for sensing each one of the emitted light pulse signals, and means connecting said sensing means to said reset terminal for controlling said emitting means to modulate the duty cycle pulse width of the emitted light pulse signals to compensate for transmission variations not constituting an interruption of the light beam. 9. The photoelectric system set forth in claim 8 further comprising a detector for generating an interrupted alarm output signal during each interruption of the light beam, said detector comprising a bit-stable logic element having an input terminal connected to said memory element and a clock terminal connected to said clock source. Other info: Inventors: Kinder, George William (Columbus, OH, US) Application Number: 641274 Filing Date: 1975-12-16 Publication_date: 1977-10-18 Assignee: Bell Telephone Laboratories, Incorporated (Murray Hill, NJ) Primary Class(es): 250/205 250/214AG, 250/552 Other Classes: US Patent Ref:
Other Refs: Other References: Thomas, Jr. and Tyndall, Jr. "Digital Feedback Light-Emitting Diode Control" IBM Technical Disclosure Bulletin, vol. 16, No. 8, Jan. 1974. | |