| 摘要 |
Facing each other diagonally across a pipe for flowing fluid is a pair of like, transmitter-receiver units operating with signals of supersonic frequency. The units are in a joint circuit and periodically are simultaneously energized to transmit identical signals to each other in opposite directions in high frequency bursts, each burst being of a chosen number of cycles and being shorter than the transmission time between the units. The bursts, received between successive transmissions, are phase shifted with respect to each other, resulting from one burst being speeded up and the other burst being slowed down in accordance with the velocity of the liquid traversed. The received bursts, in sine wave form, are heterodyned with a cosine wave form modulating signal to produce a sine wave resulting signal dependent upon phase difference between the bursts and at a low frequency. The modulating signal frequency is chosen so as to translate the multiple cycles of each high frequency burst into but one cycle in the resulting signal. The signal is manipulated electronically and its zero-crossings are demarked on a time base to establish the interval between them as a measure of the velocity of the liquid independent of sonic velocity. |
