GB1507637A - Acoustic flowmeter - Google Patents

Abstract

1507637 Acoustic flowmeters PANAMETRICS Inc 12 Nov 1976 47136/76 Heading G1G In an acoustic flowmeter of the type comprising upstream and downstream transducers 11, 13 which alternately transmit and receive acoustic energy, the energy transmitted in each direction consist of a gated burst of a frequency comprising at least a measurement frequency, and there is provided narrow band filter means 45 and 47 for extracting the measurement frequency component of the downstream and the upstream received signals respectively to provide first and second continuous sine-wave signals respectively, and timing means for measuring the phase difference between the two sine-wave signals, which phase difference is proportional to flow velocity. In Fig. 1, the measurement frequency of 5 MHz is modulated by a 2 KHz signal to provide 50 Á sec bursts, and the sine-wave outputs of filters 45, 47 are mixed at 49 and 51 with a 5À002 MHz signal to provide respective hetrodyne signals at 2 KHz which preserve the phase information. The envelopes of the received signals are also detected and processed to determine their phase difference, this also being used to determine the flow velocity. In Fig. 3 (not shown), a 100 KHz carrier is modulated by a measurement frequency of 5 KHz, this modulated signal then being modulated by a 20 Hz signal to provide 50Á sec bursts. The received signals, before being applied to the filters 45 and 47, are applied to respective detectors and filters to recover the 5 KHz measurement frequency component.