Abstract: In a textile machine two primary yarns are fed under relatively low longitudinal tension from respective yarn supplies to a combining location at which they are combined into a single yarn. The combined yarns are fed from this location under relatively high longitudinal tension to a takeup station where they are wound up on a spool. The tension in the combined yarns is continuously monitored between the combining location and the takeup station and an output is generated when this tension drops from the high tension below a predetermined level at least equal to the relatively low tensions in the individual yarns. This occurs when one of the yarns breaks. The yarn feeds are interrupted when the output is generated to prevent forming an inadequately plied yarn.