A control system for a heated conduit in a respiratory apparatus includes a power supply configured to provide power to the heated conduit and a heating control circuit configured to control an amount of heat generated in the heated conduit. The control system further includes a sensing circuit configured to indicate the temperature of a sensor positioned in the heated conduit by comparing a reference voltage with a sum of a voltage drop through the sensor and a voltage provided to the sensor by the power supply when the heating control circuit is on. When the heating control circuit is off, the voltage drop through the sensor is solely due to current provided by a current source.