Weft thread brake responsive to yarn characteristics in a loom

A weft thread brake for a loom, comprising brake force application members (1A, 1B) forming a thread gap for the passage of a weft thread (10) through said thread gap, a brake force control motor (M) connected to at least one of said brake force application members for controlling a brake force, a programmable closed loop control unit (3) connected to said control motor, an input-output unit (9) connected to said programmable closed loop control unit (3), a thread tension sensor (2) arranged downstream of said brake force application members (1A, 1B) as viewed in a weft thread travel direction and connected to said programmable closed loop control unit (3) for supplying an actual thread tension signal to said programmable closed loop control unit (3) to control said brake force by a brake force control signal in dependence on said actual thread tension signal, wherein said programmable closed loop control unit (3) comprises a memory (3A) connected to said input-output unit (9) for storing in said memory rated yarn specific weft thread tension values which are taken into account by said control unit (3) in producing said brake force control signal, and wherein said programmable closed loop control unit (3) further comprises a signal comparator (3B) connected to said thread tension sensor for receiving said actual thread tension signal and connected to said memory (3A) for receiving said rated yarn specific weft thread tension values for producing said brake force control signal as a function of one of an insertion time t of a weft thread into a loom shed and an angular rotation of a main loom drive shaft, to determine the time and size of a brake force application.