Method and apparatus for monitoring the tensile force on a thread

Abstract

A device for monitoring the tension on a thread comprises a frame for retaining the thread; a leaf spring on the frame for bearing against the thread and being displaced thereby as a function of such tension; a generator, such as a permanent magnet on the leaf spring, for generating an electromagnetic field between the frame and the leaf spring which varies as a function of such displacement; a Hall effect sensor which senses such field and generates an output signal indicative of such tension; and an electronic system for receiving said output signal and indicating whether said output signal and thereby said thread tension is within a predetermined desirable range. The indication is made at least at a location in the vicinity of the frame where it can be seen by persons who are responsible for maintaining the correct thread tension, and may comprise a plurality of LEDs for indicating respectively when the thread tension is too high, too low, and at the correct level. A method and device are also disclosed wherein the AC component of the sensor output is detected, and compared against an upper limit voltage and a lower limit voltage to determine whether the AC component above the upper limit voltage or below the lower limit voltage, and a respective LED is lit to indicate whether the AC component and the thread tension is too low, too high, or within the desirable range.