I use 1 MHz transducer to send and receive ultrasonic signal, but the problem is there is no delay between transmitted and received signal. I receive signal as soon as signal transmitted. I just see that after turning off the transmitter I have a damping wave at receiver with duration around 4 to 5 micro seconds. but this delay time does not change with distance or flow so I thought that it is not related to signal echo. I don't use any circuit know and I just use signal generator and digital oscilloscope. I will be glad if anyone help me to solve this problem.
If you do not see the phase change with the distance, then probably what your detect is the direct transmitted signal. I would first try to isolate receiver and transmitter acoustically, then make the propagation length greater than 5 microseconds times the sound speed, so that the transmitted burst and the received one are separated in time, and block the receiver electronically for the time interval of transmission.
How are the receiver and transmitter coupled to the fluid?
they are both put on the pipe using magnet at the same side. the distance between them is around 3 cm. How is it possible to detect the direct transmitted signal when I probe the receiver sensor by oscilloscope directly?
Could it be that the wave travels in the pipe wall, from the transmitter to receiver? In this case you would see the time lag when moving receiver away. If the time lag does not change, you probably see the electromagnetic influence. Detach either receiver or transmitter from the pipe; do you still see that signal?
thanks for your answering. I found out that it was electromagnetic signal that was emit from cables. I also saw that signal reaches to receiver output via VCC and GND because of low PSRR. Now I solve the problem.
best wishes,
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