APPARATUS FOR DETECTING OXYGEN CONCENTRATION

摘要

PURPOSE:To highly accurately detect oxygen concentration by means of a pumping current value and prevent deterioration in emission to suppress an exhaust amount of the emission within a regulated value by suppressing the pumping current to 70% or lower of the threshold current. CONSTITUTION:A differential amplifier 201 outputs a signal proportional to potential difference between terminals 1013 and 1014 of a sensing cell 101. An output of a voltage comparator 202 drops when the output of the amplifier 201 rises with voltage of a reference voltage source 203 as reference, and it rises when the latter drops. Terminals 20411, 20412 of a voltage comparator 2041 of an applied voltage control circuit 204 are of the same voltage. Pumping current when the electromotive force is constant flows to a flow detecting resistor 205, and a differential amplifier 206 outputs a signal proportional to potential difference between both ends of the resistor 205. O2 concentration is measured based on the signal. Since voltage of a power source 203 is set to a value that electromotive force when the pumping current is 70% or less of a threshold current value is multiplied by an amplification magnification of the amplifier 201, electromotive force at a pumping cell 102 is constant at 20mV and the pumping current will not exceed 70% of the threshold current.