GENERATION DEVICE OF REFERENCE VALUE

摘要

PROBLEM TO BE SOLVED: To generate a reference value corresponding to clean environment by creating a histogram from the time series of the output of a sensor and extracting a peak corresponding to the minimum concentration of a detection target substance from the histogram as a reference value. SOLUTION: After waiting for eight hours since a power is fumed on, a histogram memory 38 is cleared and a histogram starts to be created at a sampling interval of for example 30 seconds. A D/A converter 40 generates a reference voltage C where an offset is added to a reference EMF and is added to the positive input side of a differential amplifier 24. The difference between the reference voltage C and the output of the CO. sensor 2 is differentially amplified by a differential amplifier 24, an electromotive force that is obtained by A/D conversion by an A/D converter 34 is restored to the original electromotive force by a temperature correction part 36 and is subjected to temperature correction, thus obtaining an electromotive force EMF* that has been subjected to temperature correction. A minimum concentration peak detection means 42 searches the histogram that the histogram memory 38 stores from the side where the EMF* is larger, sets the maximum value of data before the frequency decreases as the minimum concentration peak value, and calculates the reference EMF from the peak value by conversion.