| abstract |
(57) [Summary] [PROBLEMS] To provide a configuration that does not affect the measurement accuracy even if the composition in a host gas changes. A measuring chamber (2; 30) for receiving a gaseous substance to be monitored, and the chamber (2; 3). Acoustic velocimeter (8, 10, 14, 16; 3) for detecting the acoustic velocity in 0) and providing an output indicating this. 8, 40, 44, 46), the measuring chamber (2; 30) has a wall portion (6; 36). Is provided, whereby gaseous substances to be monitored are selectively permeated between the reference gas inner chamber (2; 30) and the host gas outer chamber (2; 30). |