to be controlled in advance as shown by the curve r2 this has the advantage that the changes in the actual warp tension virtually occur at the right moment i e when the transitions p1 to p5 occur in the cloth in order to counter the inertia of said system it is also possible to build in a brief amplitude overshoot in the variation of the reference value as shown in curve r3 in this way the warp tension actually obtained will respond very quickly to the signal 29 the variations of the curves r1 r2 or r3 as mentioned above can be stored in the memory of the control unit 23 in order to make the variation of the reference value r which is produced by signal 29 and which represents the desired warp tension synchronous with the control of the weaving machine parts which determine the weaving pattern use is made of the trigger signal tr produced by the pulse generator 24 mounted on the main shaft of the weaving machine this signal tr is represented schematically in fig4 as a function of the number of crank angle degrees x of the main shaft in order to effect the changes in the reference values according to the curves r1 r2 or r3 the number of pulses per cloth length w can be counted whereby a certain pulse can be used to supply the exact reference value r to the control element 30 at the right moment if the trigger signal emits ten pulses per rotation of the main shaft as in fig4 the signal 29 can be corrected every tenth of.