one of a using a drum having a highly reflective surface and detecting the reduction in reflection caused by the loops of weft yarn or b using a non reflective drum and sensing the increase in reflection induced by the weft yarns intercepting and reflecting the beam the selection of the above mentioned alternatives of course is made in view of the colour and texture of the yarn being used in the loom a picking device generally denoted by the numeral 46 is mounted on the frame 12 in a manner essentially coaxial with the shaft 14 and drum 26 interposed between the picking device 46 and the drum 26 is a guide 48 this guide is formed with an aperture 50 the center of which is essentially coaxial with the drum a proximity switch arrangement 52 is mounted on the loom frame this switch shown in greater detail in fig3 comprises a stationary member 54 which includes a 34 hall effect 34 switch or the like and a movable element 56 fixed on a main shaft 58 of the loom the movable member 56 is arranged to pass by the stationary member 54 either at or in a timed relation with the picking operation of the loom the output of this switch is fed to a control circuit 60 which also receives the output of the sensor 44 in this embodiment a sensor 62 is mounted on the picking device side of the.