| 摘要 |
To permit this flowmeter to automatically operate either on one measurement principle or on another depending on a selectable foreign-particle content of the fluid, it has a first pair of ultrasonic transducers, one of which is operated as a transmitting transducer and the other as a receiving transducer or vice versa, and which are mounted on the outside surface of a fluid-carrying pipe and separated by a given distance in a direction parallel to the axis of the pipe, with the angle between the direction of the ultrasound and the pipe axis differing from 90 DEG . There is provided a second pair of ultrasonic transducers which are operated simultaneously as transmitting transducers or receiving transducers and are mounted on the outside surface of the pipe and separated by a given distance in a direction parallel to the axis of the pipe, the angle between the direction of the ultrasound and the pipe axis being less than or equal to 90 DEG . Driver/evaluation electronics either supply the ultrasonic transducers of the first pair successively with a pulse burst, measure the travel time in the downstream and upstream directions of the ultrasonic signals propagating through the fluid and reflected at the opposite inside surface of the pipe, and determine volumetric flow rate therefrom, or supply the ultrasonic transducers of the second pair with the pulse burst simultaneously, measure the time difference between signals reflected at foreign particles in the fluid and received by those ultrasonic transducers using correlation techniques, and determine volumetric flow rate therefrom. Changeover electronics with a threshold switch switch the driver/evaluation electronics to the travel-time or correlation mode in response to the output of the threshold switch.
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