Cross-Correlation Flow Measurement — A History and the State of the Art

Ideally, Rxy (T) is characterised by a clearly defined peak at a value of delay equal to the transit time of the fluid flow between the two sensors. Such an idealised cross-correlation function is shown in Fig 2. The velocity is easily calculated from this delay and the known transducer separation. It would appear to be a simple matter to design a signal processor to compute the cross-correlation function, determine the value of delay corresponding to the cross-correlation peak, and, knowing the effective transducer spacing, calculate the flow velocity. In practice, a measure of both the effective transducer spacing and the exact value of the flow transit time present a number of problems. One early concept assumed that a cross-correlation flowmeter will compute an absolute velocity measuremen t because only distance and time -->-7 Flow