the invention is concerned with an electronic device for testing and controlling the clearing action of an electronic yarn clearer . the device comprises an individual fault measuring circuitry connected to the yarn sensing head of the yarn clearer for detecting yarn faults such as thick and thin places , and selector means for separating the non - tolerable faults from the rest . by comparing the output of the device and the output of the yarn clearer , the non - tolerable faults which have not been cut - out by the yarn clearer are detected . it is possible to eliminate also the latter faults from the yarn by actuating the severing device of the clearer .