MY100831A - Signal compensation circuits. - Google Patents

Abstract

A DETECTION SYSTEM FOR A SLIDING LIFT OR ELEVATOR DOOR COMPRISES AT LEAST TWO SENSORS (24, 26) FOR MONITORING THE DOOR OPENING. THE SENSORS (24, 26) ARE ARRANGED TO DETECT THE PRESENCE OF MOVING IRREGULAR SHAPE (E.G. THE HUMAN FORM) IN THE DOORWAY TO REVERSE THE OPENING ACTION OF THE DOOR OR, IF ALREADY OPEN, TO PREVENT THE DOOR FROM CLOSING. A SIGNAL COMPENSATION CIRCUIT IS PROVIDED TO PROCESS THE OUTPUT SIGNALS FROM THE SENSORS IN A SENSE TO MAINTAIN THE OUTPUT OF A FIRST SENSOR (26) AS A QUASI REFERENCE SIGNAL. A COMPARATOR (113) COMPARES THE OUTPUT OF A SECOND SENSOR (24) WITH A QUASI REFERENCE SIGNAL AND THROUGH A FEEDBACK LOOP (139) MODIFIES THE OUTPUT OF THE SAID SECOND SENSOR (24) IN A SENSE TO EQUAL THE OUTPUT OF THE FIRST SENSOR (24). THE FEEDBACK LOOP (139) CONTAINS A DELAY CIRCUIT (117,122,123,126) WHICH IS SWITCHABLE BETWEEN A LONG AND A SHORT DELAY. FOR SLOW CHANGES IN THE OUTPUT OF THE SECOND SENSOR (24) THE LONG DELAY IS EFFECTIVE BUT FOR FAST CHANGES THE DELAY CIRCUIT (117,122,123,126) IS SWITCHED TO PROVIDE A SHORT DELAY. THE COMPENSATION CIRCUIT IS EFFECTIVELY DESENSITISIED AGAINST ERRORS DUE TO DRIFT AND OTHER SLOW VARYING INFLUENCES. (FIG.1)