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Abstract

Doppler Flow Velocity Meter for the irradiation of a fluid with pulses of ultrasonic waves which are fed at a predetermined pulse repetition frequency, and for the reception of echo waves reflected by fluid particles and to emit corresponding echo signals; and having receiver connected to an ultrasonic transducer for the reception and processing of echo signals which correspond to at least two different echo waves, which are reflected by the particles in a fixed point of the flow path in response to a first and a second wave pulse emitted, in which the adjacent but separate frequency bands of the echo signal are each processed in a separate signal processing channel; The receiver containing a portion in each of the signal processing channels for carrying out a quadrature demodulation of the echo signals received from the ultrasonic transducer in each of the frequency bands, in which at the output of channels a couple of each of the quadrature signals can be obtained which define a complex measured value at each time (P(0), P(.DELTA.t), P(2.DELTA.t), . . . ); a portion in which a first output signal can be produced from the quadrature signals which corresponds to an average value of the flow velocity in the analyzed point of the flow path; a portion for the logical correlation of the first output signal with the quadrature signals at the output of one of the signal processing channels, in which signals can be produced which define complex calculated values (P(.DELTA.t/2), P(3.DELTA.t/2), . . . ), and a portion for evaluation such that information on the instantaneous value of the flow velocity is obtained over a broadened measuring range.

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