METHOD FOR MEASURING LENGTH, AND APPARATUS FOR IMPLEMENTING THE METHOD

摘要

In order to determine the length of a column of a gaseous or liquid substance or of a solid bar, a standing wave of known frequency, wavelength and/or wave velocity is generated in the column of medium or in the bar and the wave frequency is varied until at least two consecutive maxima (antinodes), two consecutive minima (nodes) or a minimum following a maximum of the amplitude of the standing wave have been detected. The length of the column of medium at known frequency and wave velocity of the standing wave generated in that column is computed from the equation where L is the length of the column of medium, c is the wave velocity, f? is thefrequency of the nth maximum and f??1 the frequency of the (n?1)th maximum. Apparatus is proposed to implement the method of the invention which comprises a loudspeaker 1 mounted in a resonance chamber 2 with a tubular acoustic exit aperture 3. The resonance chamber 2 is mounted by means of a spacer 4 a distance from the pipe 6 containing the column of gaseous or liquid substance of which the length must be determined. The spacer 4 also supports thereceiving microphone 7. To keep the acoustic pressure constant over the frequen-cy/wavelength range in the resonance chamber, the acoustic volume in this resonance chamber is kept constant by means of a regulator unit 11 with a control microphone 10. Figs. 1, 2.