An acoustic gas monitor has {TAIL ~ a measurement chamber} into which {HEAD ~ a reference gas} of known composition is received and is provided with a wall section for the selective transmission of a gaseous substance to be monitored between the reference gas internal the chamber and a host gas externally of the chamber 
into is received
An acoustic gas monitor has { TAIL ~ a measurement chamber } into which { HEAD ~ a reference gas } of known composition is received and is provided with a wall section for the selective transmission of a gaseous substance to be monitored between the reference gas internal the chamber and a host gas externally of the chamber
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL REL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH