description one embodiment of a method and an apparatus according to the present invention will now be described in greater detail with reference to the block diagram in fig1 the outline diagram in fig2 and the pulse diagram in fig3 a signal emitter of some suitable type which in response to for example parameters such as the movement of a thread 52 in the tension thereon in a loom generates an electric signal is connected to a circuit a for amplification and digitalization of the signal to provide a digital signal comprising a plurality of bits suitably the signal emitter may be of the piezoelectric type but it is also conceivable to employ other types of signal emitters the amplification and digitalization circuit is coupled to a blocking circuit b and to an and gate 30 the output of the blocking circuit b is coupled to an and gate 31 whose output is coupled to an alarm and or stop function trigger circuit c which may be a flip flop or one shot circuit of some suitable type and which may in for instance a loom be caused to emit a stop signal to the loom on the occurrence of an output signal from the and gate 31 as has been mentioned earlier there may occur in the signal from the amplification and digitalization circuit a normal and known and acceptable signal gaps however these gaps do not always occur at exactly the same position in the signal and it is necessary to inform in one way or another the monitoring circuit that it is to ignore such known normal and acceptable signal gaps in accordance with the illustrated embodiment of the present invention a synchronization pulse hereinafter designated sync pulse emitter is coupled to a circuit d which.