| 摘要 |
PROBLEM TO BE SOLVED: To constitute a fail-safe of oxygen sensor by making the reading of a limiting current type oxygen cell element lower than the actual concentration at the time of deterioration or imperfect contact of the contact points. SOLUTION: One end of a resistance 32 is connected to the inversion input end of an amplifier 30, and the other end of the resistance 32 is connected to the middle point of a voltage dividing circuit connected between the output end and the ground, and a cell element S is connected between the above inversion input end of the amplifier 30 and a reference power source 33. The resistance of this voltage dividing circuit on the ground side is formed on the same board as the cell element S. Even if this heating type sensor causes an electrical imperfect contact in the connection between the sensor part and the limiting current measuring circuit by the secular change or impact, the output signal corresponding to the oxygen concentration to be measured acts in the direction of reduction, and informs user as deficient in oxygen, even in a state where the actual oxygen concentration is safe, so that an accident can be prevented, and an abnormality of the oxygen senor can be detected by the confirmation work thereafter. |
