For ultrasonically measuring the flow of air at ordinary conditions in common pipe sizes, a simple 100-kHz transducer design often suffices, as the generator and detector of the contrapropagating waves. To prevent crosstalk, acoustic isolation is needed. Isolation can be provided by supporting each transducer between soft O-rings. When the gas is hazardous, corrosive, and at high temperature or high pressure, more rugged transducers are required. One such rugged design consists of one buffer rod inside a permanent pressure boundary. The transducer is always outside the pressure boundary and can be removed without recourse to isolation valves and insertion mechanisms.
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