Circuit arrangement for automatic level control for optical sensors with pulsed radiation, for example for surveillance equipment

• US 4,068,222 A
• Filed: 11/04/1975
• Issued: 01/10/1978
• Est. Priority Date: 11/07/1974
• Status: Expired due to Term

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Treviranus, Ulrich
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Nowicki, Joseph E.
• Application Number:
  US05/628,596
• Time in Patent Office: 798 Days
• Field of Search: 340/258 R, 340/258 B, 340/259, 340/276, 340/228 S, 340/258 D, 250/221, 343/5 PD, 356/5, 356/51
• US Class Current: 340/556
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target
• CPC Class Codes: G08B 13/187 by interference of a radiation field

Abstract

Alarm signals are produced in response to variations in the radiation conditions between a pulsed IR-transmitter and a IR receiver whose output amplitude is adjustable and which is synchronously chopped by the emitted pulses, and the adjustable output signal voltage of the receiver is compared with a reference signal voltage derived from the transmitter in a comparator which is chopped synchronously with the pulse frequency of the transmitter. The comparator is followed by a control voltage generator with an integrator stage for a control element, which controls the output amplitude of the receiver, and a decision unit, to which an alarm means and a control indicator are connected.

Claims

1. A circuit arrangement for automatic output level control for optical sensors, comprising a pulsed IR-transmitter, an IR receiver, optical means for defining the angle of transmission of the pulsed infra-red radiation and for directing reflected radiation to the receiver, means for providing automatic gain adjustment of said IR receiver in response to a control voltage, means for comparing a receiver output signal with a reference signal derived from the transmitter in synchronism with the transmitted pulses, means for generating said control voltage proportional to an output signal from said comparing means and for applying the control voltage to said receiver gain adjusting means, a decision unit including means for producing an integrated value from the output signal from said comparing means and for comparing the integrated value to a predetermined threshold value, and means for producing an alarm signal, after a predetermined waiting period when the integrated value exceeds said threshold value.

2. A circuit arrangement as claimed in claim 1, wherein the control voltage generating means comprises a transistor stage connected to a rectifier and an integrator, which is connected to a control input of the gain adjusting means.

3. A circuit arrangement as claimed in claim 1, wherein the decision unit comprises an input " or" gate, an integrator having an input connected to an output of the "or" gate, first holding means connected to an output of the integrator, an inverter connected to an output of the first holding means, an "and" gate having a first input connected to an output of said inverter and a second input connected to the output of said integrator, and second holding means connected to an output of said "and" gate.