AIR/FUEL RATIO MEASURING APPARATUS

摘要

PURPOSE:To achieve a higher reliability while eliminating control operation based on erroneous counts and protecting a detector completely, by shifting a timer to a counting standby position or a time counting position with a voltage comparator. CONSTITUTION:A changeover switch 11 is provided between the output side of a driving amplifier 7 and a pumping current supply electrode 5(5a-5d) to connect the electrode 5 selectively to the output side of the amplifier 7 or a constant current circuit 15. A timer 12 turns the switch 11 to the constant current circuit 15 at the counting standby position and at the time counting position and to the output side of a detector 1 after the end of an increment counting. A voltage comparator 14 is provided between the switch 11 and the timer 12. When the voltage between each of the pumping current supply electrodes 5a-5d is outside the range of the upper limit and lower limit assumed to damage electrodes, the voltage comparator 14 sets the timer 12 to the counting standby position while it does the timer 12 to the time counting position when the voltage is within the range of both the limits. The timer 12 is also set to the counting standby position simultaneously with the closing of a power source of an air/fuel ratio measuring apparatus.