Sign detecting system

Claim 1

AN ELECTRIC SIGN DETECTING SYSTEM COMPRISING, AN EVEN NUMBER OF NON-LINEAR ELEMENTS EACH HAVING HYSTERESIS CHARACTERISTICS SUBSTANTIALLY SYMMETRICAL WITH RESPECT TO THEIR ORIGINAL POINT, INPUT MEANS FOR APPLYING AN INPUT SIGNAL TO SAID NON-LINEAR ELEMENTS, SETTING MEANS FOR APPLYING TO SAID NON-LINEAR ELEMENTS, PRIOR TO THE APPLICATION OF THE INPUT SIGNAL, A SETTING SIGNAL TO REMOVE THE EFFECT OF RESIDUAL POLARIZATIONS PRODUCED IN THE NON-LINEAR ELEMENTS BY PRECEDING SIGNALS APPLIED THERETO, A REFERENCE STANDARD SIGNAL SIMULTANEOUSLY WITH THE APPLICATION OF SAID INPUT SIGNAL, EXCITING MEANS CONNECTED FOR APPLYING TO SAID NON-LINEAR ELEMENTS AN ALTERNATING-CURRENT EXCITING SIGNAL, OUTPUT MEANS FOR TAKING OUT FROM SAID NON-LINEAR ELEMENTS AN OUTPUT SIGNAL HAVING A FREQUENCY EQUAL TO THE SECOND HIGH HARMONIC COMPONENT OF THE EXCITING SIGNAL AND HAVING ONE OF TWO POSSIBLE OPPOSITE PHASES IN ACCORDANCE WITH AN ALGEBRAIC SIGN OF AN ALGEBRAIC DIFFERENCE BETWEEN SAID INPUT SIGNAL AND SAID REFERENCE STANDARD SIGNAL, SAID OUTPUT MEANS HAVING TUNING MEANS FOR RESONATING WITH SAID SECOND HIGH HARMONIC COMPONENT.