PURPOSE: To easily know the deterioration quantity of a humidity detection element equipped with a standard filter by calculating the difference between the humidities detected by the humidity detection element equipped with the standard filter and a humidity detection element equipped with a filter having a pore size different from that of the standard filter.
CONSTITUTION: The first humidity detection element I equipped with a filter and the second humidity detection element II equipped with a filter having a pore size different from that of the standard filter are changed over by the signal of a change-over SW control circuit 5. The humidity signals of both elements are calculated as humidities H1, H2 by a humidity operation circuit 4 through an A/D converter 3. The humidity H1 is displayed on a humidity display part 6a and a humidity operation circuit 7 calculates the difference ΔH between the humidities H1, H2 and a deterioration quantity operation circuit 8 calculates deterioration quantity from the humidity difference ΔH according to an experimental approximate formula to display the same. When the deterioration quantity exceeds predetermined one, the first and second elements are replaced with new ones.
NISHIMURA JUTARO
OKADA MASAMICHI
YOMO TOSHIO
