fig2 a the vibrating means shown is designed for sensing the movement of thread or yarn or other filament material it has the following characteristics a the vibrating means 2 is presently a flat steel spring so that the primary mode of vibration is in one dimension i e the vibration has one degree of freedom of motion restriction to one degree of freedom for vibration serves to reduce the number of permutations of frequency and amplitude generated by vibration of the vibrating means 2 b the vibrating means 2 has a resonant frequency that is significantly greater than the anticipated duty cycle or stitch frequency of the machine being monitored the resonant frequency of the vibrating means 2 is analogous to a carrier wave where the amplitude is modulated by the duty cycle c the vibrating means 2 has a notch or aperture 4 the size of the notch or aperture 4 is a function of dimensions of the needle or looper eye and the anticipated maximum filament allowable knot inconsistency dimensions when a knot or filament inconsistency impinges on the notch 4 it causes a large amplitude vibration fig2 b illustrates a slanted aperture 4 used for an acute thread path wherein thread bending contributes to knot sensitivity d the top edge of the vibrating means has a slope 5 so that yarn or filament.