Abstract: Device for measuring the speed of a fluid in a tube which comprises two uasonic electro-acoustic transducers in the tube; means for energizing these transducers by first and second transmit pulse groups; means for receiving first and second receive pulse groups at the transducer output; means for measuring a first delay between the start of the first transmit pulse group and the start of the first receive pulse group and a second delay between the start of the second transmit pulse group and the start of the second receive pulse group; and means for measuring a third delay between the starts of the first and second receive pulse groups. The flow rate is proportional to the quotient of the third delay by the product of the first and second delays. These delays comprise an integer delay part which is measured by clock pulses counting and fractional delay parts which are measured by constant current integrators.

Abstract: Recursive digital filter deriving the samples of a filtered output signal at a present sampling instant from the samples of an input signal to be filtered at said present sampling instant and at two preceding consecutive sampling instants and from samples of said filtered output signal at said two preceding consecutive sampling instants.