Patent ID: 8173938
Filing Date: 2012-05-08
Classification: H05B,Y10T

Abstract:
1. A controller for a heating cable, the heating cable comprising at least first and second conductors and a separation layer interposed between said first and second conductors, said first and second conductors and the separation layer extending along the length of the heating cable, the electrical resistance provided by the separation layer between adjacent portions of said first and second conductors having a negative temperature coefficient, the controller comprising: a first switch, arranged for connecting the first and second conductors electrically in series at one end of the heating cable such that if the first and second conductors are connected at the other end of the heating cable to respective poles of a power supply, currents flow in opposite directions through adjacent portions of the conductors; a second switch, arranged for connection in series between the first conductor and a pole of the power supply at the other end of the heating cable; a first resistor connected in parallel with the second switch; and voltage measurement means, arranged to measure voltage across the first resistor, the voltage across the first resistor when both switches are open being responsive to changes in the electrical resistance of the separation layer; wherein the controller is arranged to control the supply of power to the heating cable as a function of the measured voltage across the first resistor when both switches are open.