| 摘要 |
PURPOSE:To improve detecting accuracy by selecting either of the output from a means for detecting the current to be supplied to a partial voltage control part which controls the output from the detecting part for oxygen partial pressure of an oxygen sensor so as to coincide with a target value or the output from a means for detecting the voltage between the two 1st electrode in the detecting part and the control part while the supply current is held interrupted. CONSTITUTION:A differential amplifier 33 of a detecting circuit 32 for the concn. of oxygen over a wide range outputs the differential voltage DELTAV between the potential Vs corresponding to the oxygen partial pressure ratio of an oxygen sensor (not shown in the figure) and a target voltage Va. A supply circuit 35 for pump current controls pump current Ip to control said potential so as to attain Vs=Va. A differential amplifier 38 outputs the current Ip as output Vi. A differential amplifier 38 detects the voltage between a sensor anode 20 and a pump anode 23 and outputs the same as output Vp. An indication circuit 40 for selecting the detected output turns on a switch circuit 41 to change over a switch circuit 42 to a terminal (a) side and to emit the output Vi as the output Vc in the case of detecting the air-fuel ratio over a wide range. Said circuit turns off the circuit 41 to change over the circuit 42 to a terminal (b) side and to emit the output Vp as the output Vc in the case of detecting a theoretical air-fuel ratio. |
