PURPOSE:To suppress the space required and reduce the cost by allowing a single case to accommodate a regular length counter and a yarn clearer to sense defective parts of a yarn, by installing it on each takeup unit, and thereby compacting a yarn monitoring device. CONSTITUTION:A signal L2 given by a sensor head 19 is processed by an amplifier 27 into a proper size for processing, entered into a yarn defect judgment circuit 28 and a yarn travel sensing circuit 29, wherein the yarn defect judgment circuit 28 compares the signal level with a set value, and in case of exceeding the set value a judgment signal L3 to inform that there is defect on the yarn, to be fed into an AND gate 31 via an inverter circuit 30. The yarn travel sensing circuit 29, on the other hand, emits a signal voltage generation signal, which responds to variation of the yarn diameter, as a yarn travel signal L4. If slab is sensed, one pulse is emitted by 1 shot circuit, so that a signal line 34 is put off, and the output of the AND gate 31 will be off to stop spinning-out. These yarn monitoring devices are arranged in a compacted box and installed on each takeup unit.
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