| 摘要 |
PURPOSE:To prevent erronous operation by the deterioration in characteristics of the detector, by always calculating the ratio of the output voltage of an oxygen sensor in air to be detected to that of an oxygen sensor in normal air and detecting that the calculated value reaches a predetermined value or less. CONSTITUTION:At first, the output voltage l0 of an oxygen sensor 1 at normal oxygen concn. of 20.6% is inputted to an A/D converter 15 through an amplifier 2 to be subjected to digital conversion and the digitalized value is written in an arbitrary writing part, wherein data is always cleared in the initial state of CPU16, to be set to RAM as an initial value. Next, output voltages l2, l3... ln of the oxygen sensor 1 on and after a second time in air to be detected receive digital conversion to be inputted to CPU16 and the ratios of the writing values thereof to the initial value are operated and, when the operated values reach the reference set value preset to CPU16, an alarm buzzer 5 and a solid state relay 16 are driven by the digital output signal of CPU16. |
