Device for the photoelectric supervision of a warp loom

Device for the photoelectric monitoring of a wrap loom for irregularities in the yarn supply of a yarn sheet, comprising:

• an infrared radiation source for producing a beam passing to the eye needles in a plane parallel to said yarn sheet in the area of the yarn supply;
• an infrared radiation receiver for generating a signal depending on the intensity of said beam;
• evaluation circuit means for processing said signal;
• and a display means for responding to a control signal characterising irregularity of said yarn supply and/or a switch device for driving said warp machine, wherein the infrared source and the associated receiver are arranged so that said beam is alternately at least partially interrupted and released in synchronism with the frequency of knitting tool and/or guide bar oscillation by means of the knitting tools and the yarns processed thereby in the reversing positions of said knitting tools, and wherein a periodic monitoring signal sequence thus generated by the infrared receiver is periodically processed in said evaluation circuit by a window or gating circuit means only during a preset gating time period within each beam release phase, so that only the signal values produced in each window pulse gating phase are compared in a comparator means with a comparison value.