| 摘要 |
PURPOSE:To improve measuring accuracy in the measuring of the difference in propagating times in the flow speed measuring device employing an ultrasonic wave propagating time difference method by minimizing the variation in the time difference signal due to the noises in the received signals. CONSTITUTION:Outputs 31a and 31b of a receiver circuit are inputted to time difference signal circuits 57a and 57b. The input to said circuit 57a is further inputted to a V0 level detecting circuit 51 and a zero level detecting circuit 52. The circuit 51 which has detected a level V0 that is 2-3 times a noise level VN, generates an output 61, and sets a set reset FF 53 every time the received signal exceeds the level V0. Meanwhile, the circuit 52 generates an output 62 and resets the FF 53 every time the received signal passes the zero level. The ordinal number of the vibration having the maximum amplitude in the received ultrasonic waveforms is measured and said wave number n is set in a counter 54. A time 81, at which an output 64 from the circuit 54 based on the n-th waveform and an output 62 from the circuit 52 are concurrently generated, is detected, and an output 65a is generated. Meanwhile, an 65b is generated by the circuit 57b in the same way from the output received signal 31b. The time from the output 65a to the output 65b is measured 43, and the flow speed is measured. |
