Improvements in or relating to Aircraft De-Icing and Anti-Icing Systems

摘要

1,192,364. Protective arrangements. TEDDINGTON AIRCRAFT CONTROLS Ltd 29 Aug., 1967 [26 May, 1966], No. 23567/66. Heading H2K. [Also in Division G3] In an automatic temperature control system for the electrically heated mats 2, 4 of an aircraft de-icing system (see Division G2-G3), means are provided to automatically switch the system off upon the occurrence of excess temperature or current conditions. In the system each of a plurality of solid state switches 28 includes a transformer 34 whose core is chosen so that its Curie temperature coincides with the maximum allowable temperature of the thyristor 40 and diode 42 forming the switch. The transformers 34 are coupled secondary to primary in a chain and normally transmit high frequency firing pulses for the thyristors from a source 44 to AND gates 32 forming part of the control system. Should any one of the switches 28 become too hot, there is no output from the chain, no third input to any of the gates 32 and hence no firing pulses for the thyristors. When the temperature of the overheated switch falls, normal operation automatically resumes. Should the current through any switch 28 exceed a safe value, a respective over-current sensor 26 switches the system off by providing an input to a protection device 24 controlling the pulse width modulator 22 of the temperature control circuit. The device 24 has a second input from an arc detector 20 which detects out-ofbalance currents in the three phases in known manner and controls the device 24 to switch the system off. The over-current protection arrangement is reset by switching the system "off" and then "on" again.