| 摘要 |
A heating controller includes a source of electrical power for outputting electrical power to a heating cable which includes at least one heating element 150,152 and a calibration wire 156 that is substantially the same length as the heating element and has a substantially temperature independent resistance. The cable heating controller (fig 1, 102) includes a controller that determines the resistance of the calibration wire; calculates from it the length of the heating element; and controls the electrical power source to deliver power to the heating element according to its length. The resistance can be determined using a voltage divider, a low pass filter and an analogue to digital converter input to a microprocessor. The controller can calculate the resistance of the element from a resistance per unit length and the calculated length and can measure the ambient temperature using a sensor (fig 1, 122). The source of power can be controlled by its duty cycle and can deliver a higher power depending on whether the temperature is below a threshold. Different power settings can be input by a user. By determining the length of cable attached to it the controller can be used with different lengths of cable.
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