Control system for material handling

Claim 1

IN AN ELECTRIC CIRCUIT FOR AUTOMATICALLY CONTROLLING A MECHANICAL VALUE ASSOCIATED WITH A MATERIAL, AN ELECTRIC OPERATOR FOR CONTROLLING THE MATERIAL, ELECTRIC LINES AS A SOURCE OF VOLTAGE, A POTENTIOMETER-TRANSDUCER OPERATING FROM THE VOLTAGE SOURCE AND CONVERTING SAID MECHANICAL VALUE INTO AN ELECTRIC SIGNAL BY CHANGE IN VOLTAGE RATIO UPON CHANGE IN POSITION OF THE MOVABLE POTENTIOMETER CONTACT, MEANS CAPABLE OF BEING ENERGIZED FROM A PLURALITY OF INPUTS FOR CONTROLLING SAID ELECTRIC OPERATOR, ONE OF SAID INPUTS BEING SAID ELECTRIC SIGNAL DERIVED BY SAID TRANSDUCER, AND MEANS ENERGIZED FROM SAID SOURCE OF VOLTAGE AND COUPLED TO SAID MEANS FOR CONTROLLING SAID ELECTRIC OPERATOR FOR CALIBRATING SAID TRANSDUCER TO A MINIMUM VOLTAGE RATIO AS THE ZERO OF SAID MECHANICAL VALUE, SAID CALIBRATING MEANS COMPRISING A SECOND INPUT TO SAID MEANS FOR CONTROLLING SAID ELECTRIC OPERATOR.