Wire heated tube with temperature control system for humidifier for respiratory apparatus

A control system for a heated conduit for use in a respiratory apparatus is disclosed. The control system comprises a power supply to provide power to the heated conduit; a heating control circuit configured to control heating of the heated conduit to obtain a predetermined temperature; a sensing circuit configured to provide an output to the heating control circuit to indicate the temperature of a sensor positioned in the heated conduit and a bias generator circuit. The bias generator circuit comprises a passive resistor bridge that receives power from the power supply and provides a reference voltage to the sensing circuit to allow determination of the temperature of the heated conduit as a function of a voltage drop across an element of the sensing circuit during both heating ON and heating OFF cycles. The polarity of the sensing circuit output varies as a function of an output of the heating control circuit.