| 摘要 |
The invention relates to a method which is used to measure the flowing speed of fluids according to the transit time difference method (?T = T2 - T1), in addition to a suitable measuring circuit. In a first measuring step, an ultrasonic measuring path (11) which is arranged between two ultrasonic transducers (10, 12) is transversed in the forward direction. An emitting transducer (10) is excited with a limited number of excitation impulses (burst 1) in order to emit an ultrasonic wave train. A receiving transducer (12) receives the ultrasonic wave train as an analog signal train (W1) which is subsequently digitalised in order to form a pulse train (D1) and is counted in an impulse counter (4). The period of time extending between a determined pulse of the excitation impulse (burst 1) and an n-th pulse of the pulse train (D1) is the first period of time (T1). Subsequently, the ultrasonic measuring path (11) is transversed by means of a defined number of excitation pulses (burst 2), which have the same frequency, in the reverse direction. The wave train received by the transducer (10) as an analog signal train (W2) is digitalised in order to form a pulse train (D2). The impulse counter (4) remains inactive for the duration of a door time (TGate) which is connected to the first period of time (T1). The period of time between a defined pulse of the second excitation impulse (Burst 2) and the first pulse of the pulse train (D2), which is detected after activation of the impulse counter (4), is the second period of time (T2). The flowing speed (v) of the fluid can be calculated from the time difference (?T) between the first and the second period of time (T1, T2). |
