Implementation of digital signal processing techniques in thedesign of thermal pulse flowmeters

Various digital signal processing methods, which could be applicable to the design of a microcomputer-based thermal pulse flowmeter, are examined. Two excitation methods are investigated: a single thermal pulse, and a pseudorandom binary sequence signal (PRBS). The signal recovered downstream is processed by two alternative numerical algorithms to recover the time of flight (i.e. by peak detection of the signal itself and the peak of the differentiated signal). The recovered thermal pulse and the time of flight are then used to test the validity of two models: a diffusion-advection model and a simple time-delay model. The delay model is found to be compatible with the data, especially when the peak of the output signal derivative is used as a marker for determining the time of flight. The single-pulse injection method is found, in general, to be superior to the PRBS cross-correlation technique, except for the ability of the latter to provide early indication of flow-rate variations