Method and device for determining the speed of a gas flowing in a pipe

摘要

Acoustic flow measurement method and device for determining the flow speed of gases and/or gas derivatives. In a measuring pipe 1 two microphones 3a, 3b have been mounted at a given longitudinal distance L from each other with two loudspeakers 2a, 2b outside these, which supply sound to the measuring stretch L which is delimited by the microphones 3a, 3b, which sound is in the form of stationary broadband sequences in the direction of the flow Sd(tT) and against the flow Su(tT). The frequency range of the sequences Sd(tT) and Su(tT) is selected so that only a basic mode in the form of a flat wave front can advance without being suppressed. In addition the sequences Sd(tT) and Su(tT) are selected so that they are orthogonal to each other and have no common frequency components except for zero. The detector signals which are picked up by the microphones 3a, 3b are processed by a signal processing arrangement essentially in real time, which produces different kinds of correlation functions or Fourier transformations of the same. From these the system determines in addition different kinds of alternative algorithms by applying the transit time of the said sound in the measurement stretch L with the flow and against the flow and from these and from the cross section of the pipe and the density which was determined for the gas, determines the flow speed, volume flow and/or mass flow. IMAGE