lighting of the indicator lamp double insertion in this manner while the loom stops each time there is an irregularity in operation the operator has an immediate indication of the type of irregularity which has occurred and may rapidly restore the loom to working condition because of the possibility to program the operation of the device described by simply operating the switches in the logic network it is evident that said device has a latitude of intervention which is exceptionally wide or even complete in that none of the irregularities which may occur in feeding the weft yarns to any type of loom and in any type of weaving operation can escape its control the result is evidently of utmost importance and represents a great improvement over any known device of this type the practical construction of the device obviously requires particular care from experiments made so far it has been found for example that the transducers must be able to detect also the movement of fine smooth and regular yarns producing only a very small or negligible tension on the yarn and this because in gripper looms the weft yarn must have maximum freedom of movement and must therefore not undergo any external stress on the other hand the transducers must also provide a high signal disturbance ratio which is not objectively simple in machines such as looms.