The appts. to mend a broken yarn by thermal splicing, using heated air delivered under control to the splicing chamber, has a thermal sensor (90) with a small response time where the splicing air meets the splicing chamber (11). The sensor (90) generates a control signal to control the heater (58), to regulate the air temp.. The thermal sensor (90) registers the splicing air temp. and/or the time changes of shifts in temp. The thremal sensor (90) is formed by a thin layer resistance, such as a film thermometer, to give an electrical resistance responsive to temp.. The thin layer for the thermal sensor (90) is of Pt or Ni, as a deposited layer on an electrical insulator, such as on a heat resistant ceramic component, on to which the thin layer is deposited under vacuum and then fired. The thermal sensor (90) is a dedicated component, at a wall section or in an opening in the splicing chamber (11), or at its cover (12). The thin layer for the sensor can be deposited directly on the chamber wall section or the cover (12), to be covered by a protective layer resistant to mechanical forces. At leat one control unit (89) controls the heater (58) to regulate the splicing air temp., according to the signals from the thermal sensor (90), so that the heater (58) operation follows the thermal reading. The thermal sensor (90) is preheated by an electrical voltage of a given level passing through it and/or through a heater at the sensor. ADVANTAGE - The system gives better temp. control and gives an improved yarn bonding splice.
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