also the sole circuit delivering the actuating pulse for the blocking or separating devices assigned to the individual materials the device shown in fig2 is especially suited because of its simple structure for use with machines in which also more than two starting materials are processed to an end material for instance twisting machines in which a twisted yarn is manufactured from three feed materials each of the three feed materials is then assigned a sensor assembly and a separating device and a sensor is also directed to the manufactured twisted yarn the alternating currents generated from the modulated radiations of all sensors are then fed to the common and operator and identification circuit and the latter delivers the actuating pulses to the three separating devices connected with it in the event of failure of any one of the four modulated radiations one of the cable connections between the identification circuit 135 and the electomagnets 37 and 60 respectively illustrated in fig2 can if need be be dispensed with if the collective housing 56 and the housing containing one of the magnets are structurally combined as by mounting the cutting device 60 on the housing 56 the arrangement shown in fig3 is particularly suited for use with machines producing one end material from two starting materials in this case a sensor assembly and a blocking or separating device are assigned to each starting material the former acting to cross switching the latter.