Alvin W Edson

US Patent:

43273718, Apr 27, 1982

Filed:

Dec 19, 1979

Appl. No.:

6/105067

Inventors:

Alvin W. Edson - Binghamton NY
Richard A. Windyka - Chenango Bridge NY

Assignee:

The Singer Company - Binghamton NY

International Classification:

H04N 962

US Classification:

358 10

Abstract:

A method and apparatus for quickly and easily calibrating a relatively unstable light detector, such as a photomultiplier tube. The system is particularly designed to effect large scale semi-automatic calibration of many photomultiplier tube-preamplifier combinations that may exist in, for example, a laser scanner system. Each preamplifier (10) includes an automatic gain control circuit (20) connected in a loop which is momentarily closed during a calibrate mode when a predetermined level of a calibrated light source (15) is directed upon the associated tube (12). An error amplifier (34) develops a voltage in accordance with the deviation of the video output of the tube from the expected level during calibration, and the error voltage is preferably stored in digital form (38) so that the gain of the preamplifier (10) may be maintained at the calibrated level between successive calibrations. The calibrated light source (15) is chopped to provide alternating bright cycles and dark cycles during the calibration mode. The preamplifiers are calibrated during the bright cycles, while the dark cycles are utilized to restore the direct current level of the video output signal, which restoration occurs in normal operation during horizontal blanking of the video system.