Disclosed is a control system for a heated conduit for use in a respiratory apparatus. The control system includes a power supply to provide power to the heated conduit and a heating control circuit (450) configured to control heating to obtain a predetermined temperature. A sensing circuit (428) includes a sensing resistor (426) configured to provide an output to indicate the temperature of a sensor positioned in the heated conduit. A bias generator circuit (418) provides a reference voltage to the sensing resistor (426) to allow determination of the temperature of the heated conduit as a function of a voltage drop across the sensing resistor (426) during both heating on and heating off cycles. A direction of the voltage drop across the sensing resistor (426) changes when the heating circuit (450) is on compared to when the heating circuit (450) is off.
