Abstract: A novel construction of a control plate inserted within and corresponding to a system of plates of a picking comb of a fluid-jet loom is described. The exit opening of the control plate has a detecting section including a light source and a photocell disposed in aligned spaced relation on opposite sides of the exit slot. The width of the exit slot is narrowed, at the location of the source and photocell, to a dimension substantially equal to the diameter of the weft thread exiting from the picking space of the control plate. At least one of the light source and photocell projects into the narrow exit slot to assure an enhanced wiping action of the weft thread on the detecting elements as the weft thread moves through the exit slot.