A method and apparatus for monitoring the production of spun yarn in an open end rotor spinning machine. The spun yarn is withdrawn from the open end rotor spinning machine at a constant rate of speed. As a result of changes in mass of the yarn created by flaws therein, the centrifugal force within the rotor varies causing the tension in the yarn to vary accordingly. As the yarn is withdrawn from the rotor, it passes around a spring loaded arm which is displaced according to the centrifugal force applied to the yarn. The spring loaded arm is operately connected to a balance bridge circuit which generates an output signal corresponding to the displacement thereof. The output signal from the balance circuit is then fed to an integrator which integrates the signal to produce a slowly varying integrated reference signal. The output signal from the bridge circuit is also converted into a short time or instantaneous signal that is compared with the integrated signal for producing an out of tolerance signal if and when flaws occur in the yarn. The system produces an out of tolerance signal resulting from thin spots, thick or heavy spots, and/or breaks within the yarn.
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