Abstract
The paper discusses principles of a digital multigate system for Doppler frequency measurements. The conception of a system with serial data processing, based on the Doppler frequency measurement with the "zero crossing" method, is described. Problems with the recognition of the direction of flow in the digital system are presented, as well as two solutions, tested in practice, which limit occurring measuring errors. An example of an actual flow measurement made with the application of a model of the presented device is described, and possible errors resulting from the "zero crossing" technique are given. In order to improve properties of the system the use of a digital low-pass filter is proposed. The conception of such a filter is described.References
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[2] A. P. G. HOEKS et al., A multigate pulsed Doppler system with serial data processing, IEEE Trans. on Sonics and Ultrasonics, SU-28, 4. 242 -247 (1981).
[3] A. NOWICKI, J. REID, An infinite gate pulse Doppler, Ultrasound in Med. and Biol. 7, 41-50 (1981).
[4] B. A. NANGEISEN, J. KRISTOFFERSEN, On ultrasonic MT1 measurement of velocity profiles in blood flow, IEE Trans. on Biomedical Engn. BME, 26, 12, 665-671 (1979).
[5] M. J. LUNT, Accuracy and limitations of the ultrasonic Doppler blood velocimeter and zero crossing detector, Ultrasound in Med. and Biol. 2, 4-10 (1975).
[6] J. H. NIPPA, Phase rotation for separating forward and reverse blood, velocity, IEE Trans. on Sonic and Ultrasonics, SU-25, 5.
