| 摘要 |
PURPOSE:To control the temp. in the heating part of a four-terminal type heater with good accuracy by providing a resistor for temp. setting in series to said heater and controlling the heater current in such a manner that the difference in the voltage drop between the heating part of the heater and the resistor for temp. setting is made zero. CONSTITUTION:The four-terminal type heater is constituted with the heating part (a) to heat an oxygen detecting part, lead parts (b), (c) for the part (a) and lead parts (d), (e) to detect the electric signal between the lead parts (b) and (c). The four-terminal type heater is connected in series to the resistor Rs for temp. setting. The resistor Rb in the lead part of the four-terminal type heater is connected at one end to the resistor Rs and the resistor Ra in the heating part of the four-terminal type heater is connected at one end to the lead part Rb. The resistor Rc at the lead part is connected at one end to the heating part Ra. The voltage drop of the temp. setting part Rs is connected to an operational amplifier 105 and the voltage drop of the heating part Ra is connected to an operational amplifier 110. The output voltages from these amplifiers are inputted to a differential amplifier 120 and the heater current is so controlled that the differential voltage between the resistor for temp. setting and the heating part is made zero. |
