| 摘要 |
PURPOSE:To enable following-up in a short time at the time of recovery of a received wave even when flow rate or sound velocity is changed while propagation is hindered, by determining the normality and abnormality of the received wave based on the number of times when a received-signal level exceeds a reference level. CONSTITUTION:The received wave is amplified 32 and sent to a comparison circuit 33 as a received signal S1, and when it is higher than the reference level L from a voltage source 34, a signal S2 is delivered. The signal S2 is sent to a measuring circuit 38 and there a pulse for measuring a time is prepared, and based on this pulse and a transmitted signal, the time T for propagation be- tween a transmitter and a receiver 2 and 3 is measured. Moreover, the signal S2 is counted by a counter 36 and a count value is sent to a discrimination circuit 37. When being within prescribed limits, it is discriminated as a normal received wave, and when being outside the prescribed limits, it is discriminated as an abnormal received wave, and the result of the discrimination is outputted to the circuit 38. Accordingly, the circuit 38 detects the normality and abnormality of the received signal on the basis of the result of the discrimination. |
