887,547. Testing yarns &c. ZELLWEGER Ltd. June 20, 1960 [Sept. 11, 1959], No. 21610/60. Class 120(3) [Also in Group XXXVI] In a method and apparatus for detecting and removing objectionable cross-section variations in yarns or other textiles, a signal produced in or by a measuring member is fed to a Schmitt trigger circuit and any output pulse arising from a signal amplitude exceeding the trigger voltage is applied through a differentiating network to trigger a monostable trigger pair to produce a pulse of sufficient duration to actuate severing means. The output from an inductively coupled transistor oscillator 9, Fig. 3, is fed to a measuring member comprising condensers 11-14 through which the yarn is passed, the measuring signal U 1 is rectified in a network 2 and then passed to a difference amplifier comprising transistors 31, 32, feed back from a succeeding low frequency amplifier 33 being provided through a resistor 306. The Schmitt trigger pair 41, 42, Fig. 4, has a shunt 43 across its input which may alternatively be connected to a variable voltage source whereby the trigger voltage may be adjusted, and its output is differentiated, in C.R. network 51, 52 before being applied to the base of transistor 6 ofthe monostable pair 61, 62. The output pulse U5, of predetermined duration is power amplified by transistors 71, 72 and applied to operate electro magnetic severing means 8. A rectifier 82 is provided for surge suppression at switch-off. An arrangement for adjusting the sensitivity of a group of devices mounted on a single machine by controlling the oscillator D.C. feed voltage is described with reference to Fig. 5 (not shown).