Yarn defect detector apparatus for textile machinery

Claim 1

Yarn defect detector comprising a measuring head (30) having yarn (50) passing therethrough; a signal transfer circuit including an amplifier (31) and discriminator means (35; 14, 15, 16, 17) selecting signals (53) indicative of thickened sections in the yarn (50) passing through the measuring head; a reference source (39) supplying a reference potential (UR); comparator means (37) connected (44, 38) to said reference source (39) and further connected (36) to the output of said amplifier (31) and providing an error signal upon deviation of output signal (Uo) from the predetermined level; means (32) controlling the amplification of said amplifier (31) to set the output signal (Uo) of the amplifier corresponding to nominal standard yarn thickness at a predetermined level (51) and memorizing the control setting thereof; means (33) connected to the output of said comparator means (37) and controlled by the error signal thereof controlling said amplification control means (32) of the amplifier to null the error signal; and switch means connected into the control loop formed by the comparator (37) and said amplification adjusting means (33), said switch means being controlled by the yarn drive to interrupt the control loop circuit upon interruption of yarn motion, the amplification control means (32) storing the setting thereof upon interruption of the control loop circuit and being effective to control the amplification of said amplifier starting from the control setting prior to interruption, upon resumption of yarn motion.