| 摘要 |
PROBLEM TO BE SOLVED: To correct secular change for which measuing precision for an ammonia gas concentration measurement is lowered caused by deterioration of a catalyst for ammonia reduction, so as to secure the measuring precision. SOLUTION: A heater 6 is provided to heat a sample gas sucked in a front stage part of a reaction part 2 inside an ammonia gas sampling probe container 1, and a heater control part 17 is provided to control the heater 6 and a temperature of the heater 6 from the control part 17. Periodical control between a low temperature in a usual measuring time (about 400 deg.C) and a high temperature for a correcting value measurment (about 700 deg.C) is conducted to measure NOx concentrations in an NOx line 9 and an NH3 line 8 at the time of the high and low temperatures, reduction efficiency of a catalyst is calculated by a computing element 15 and a correcting circuit 16 based on measured values therein, and the reduction efficiency is evaluated to conduct correction as to catalyst deterioration.
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