Multiple time difference ultrasonic flowmeters

Claim 1

In a flowmeter of the type wherein at least one pair of oppositely disposed ultrasonic transducer means are located in acoustic contact with a fluid stream and in upstream-downstream relation thereto; a first feedback path couples the output of a first of said tranducer means to the input of a second of the transducer means such that upon one acoustic signal being transmitted upstream from the second transducer means to the first transducer means the transmission of another acoustic signal upstream is initiated from said second transducer means when said one upstream acoustic signal is received by said first transducer means, thus generating an upstream train of acoustic signals in sing-around fashion; a second feedback path couples the output of said second transducer means to the input of said first transducer means such that upon one acoustic signal being transmitted downstream from said first transducer means to the second tranducer means the transmission of another acoustic signal downstream is initiated from said first transducer means when said one downstream acoustic signal is received by said transducer means, thus generating a downstream train of acoustic signals in sing-around fashion; the combination of: gating means for causing said upstream and downstream trains of acoustic signals to occur between said first and second transducer means during respective and successive first and second predetermined time intervals, said first and second predetermined time intervals being different from each other; means for deriving from the acoustic signals in each of said trains an elementary time interval characteristic of the fluid stream velocity; said elementary time interval increasing by Delta t increments from one transmitted acoustic signal to the next; means coUpled to said deriving means for generating a first sum signal representing the sum of said elementary time intervals through said first predetermined time interval proportional to: Delta t + 2 Delta t + 3 Delta t + . . . + N Delta t where Delta t is the elementary time interval for the first acoustic signal in the corresponding train of acoustic signals and N is the number of acoustic signals transmitted and received successively occurring during said first predetermined time interval and for generating a second sum signal representing the sum of said elementary time intervals through said second predetermined time interval proportional to: Delta t + 2 Delta t + 3 Delta t + . . . + N'' Delta t where Delta t is the elementary time interval for the first acoustic signal in the corresponding train of acoustic signals and N'' is the number of acoustic signals transmitted and received successively occurring during said second predetermined time interval; and means responsive to said sum representing signal for each of said different predetermined time intervals for deriving first and second sum signals for providing signal combination thereof; said first and second predetermined time intervals being such that N N'', and the difference between said first and second predetermined time intervals being less than the nominal travel time between said first and second tranducer means for the condition of no fluid flow therebetween, thereby to compensate for deviations in each of said sum signals due to change in the speed of sound.