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M. Kupnik, A. Schröder, P. O´Leary, E. Benes, M. Gröschl:
"An ultrasonic transit-time gas flowmeter for automotive applications";
in: "Proc. IEEE Sensors 2004", D. Rocha, P.M. Sarro, M. Vellekoop (Hrg.); IEEE, 2004, S. 451 - 454.

A new concept for ultrasonic transit-time gas ?owmeters,
utilizing high temperature resistant capacitance transducers,
and results from a preliminary laboratory prototype,
are presented. With this concept measurements of hot (up
to 450 ?C) and pulsating gas ?ows have been achieved for
the ?rst time. Such conditions occur e.g. in an exhaust gas
train of a combustion engine. An adaptive pulse repetition
frequency (PRF) is used to overcome the problems associated
with the range and dynamics of the gas temperature.
Large temperature variations prevent a continuous detection
of ultrasonic pulse arrival times. Coherent re?ections are
generated, since the acoustic impedances of the gas and the
transducers are mismatched. Depending on the gas temperatures
these re?ections may overlap with the actual signal.
The presented method renders feasible a correct detection
over the whole temperature range. Results are presented for
the mass ?ow rate in a ?50 mm pipe measured at a PRF up
to 5.5 kHz.

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