| 摘要 |
PURPOSE:To prevent the deterioration in the characteristic of a sensor caused by contamination, by supplying at least binary voltage to the indirect heater of the sensor. CONSTITUTION:In the detection circuit of a heating apparatus having a sensor equipped with an indirect heater 5, a square signal R3 is applied to the sensor chip 6 through a driver 20 and a condenser 21. The change in the resistance of the sensor is amplified by an amplifier 22 and guided to the input A/D of an A/D converter through a smoothing circuit 23. The voltage source 24 of the indirect heater 5 receives at least binary control is its output voltage by the signals R1, R2 of a control part 9. A resistor group 25 creates the reference voltage of said output voltage along with a voltage follower 26. The control part 9 has a timer and, if the time elapsed from the completion of heating reaches a definite value, higher output voltage is supplied to the indirect heater 5 to burn off the contamination of the sensor chip 6. By this method, cleaning can be performed in clean air in which no impure gas is present. |
