COMPARISON DISCREPANCY INDICATOR FOR RECORDS

摘要

1,220,103. Monitoring records. BELL & HOWELL CO. 5 April, 1968 [7 April, 1967], No. 16452/68. Heading H4J. [Also in Divisions G1 and G5] A discrepancy indicator for comparing mechanically, magnetically, optically or electrostatically recorded master and copy signals is designed to give error indication signals when the copy signal falls below two different levels, e.g. 3db and 6db, relative to the master signal. The master record MR is played back by head 30 and the signal amplified, equalized and fed to copy recording heads 46, the master and copy records being subsequently played back by heads 29, 45 for comparison. The master signal is amplified 21, rectified 25 and integrated 27 to give a slowly varying positive D.C. voltage on line 43. Each copy channel is divided into two similar subchannels which, via potentiometers 65a, 65b provide slowly varying, negative D.C. voltage levels on lines 75a, 75b at a nominal 3db and 6db above the D.C. level on line 43. The outputs from the respective copy subchannels are compared with the master signal in zero-crossing detectors 77a, 77b to operate trigger circuits 81a, 81b associated with SCR-controlled warning lamps 113a, 113b when the signals on the respective copy subchannels fall to their 3db and 6db limits. The drive to the offending copy is preferably halted when the 6db limit is reached. The stop control relay 119 is also associated with normally open and closed contacts 123, 125 respectively, arranged to apply a pseudovoltage V 3 to the rectifiers 57a, 57b to prevent the indicators operating when copying is not in progress.