Pulse train detection in transit time flowmeter

Claim 3

A method as in claim 1, further comprising the step of selecting a transmit frequency fx for the ultrasonic pulses to be transmitted.

Claim 4

A method as in claim 2, further comprising the step of transmitting a short pulse train between said transducers and determining the total elapsed time t N the short pulse train takes to travel between the transducers.

Claim 5

A method as in claim 3, wherein the step of determining the total time in liquid t L is carried out by subtracting a known conduit transmit time from t N .

Claim 6

A method as in claim 3, wherein said short pulse train comprises 3 cycles of said frequency fx.

Claim 7

A method as in claim 1, further comprising the steps of: selecting a transmit frequency fx for the ultrasonic pulses to be transmitted; and transmitting a train of N ultrasonic pulses Tx at said frequency fx.

Claim 8

A method as in claim 6, wherein N is between 8 to 100 inclusive.

Claim 9

A method as in claim 6, further comprising the step of receiving a received pulse train Rx and digitizing a steady-state portion thereof to generate a signal Rd.

Claim 10

A method as in claim 8, further comprising the step of determining a phase difference between said signal Rd and a phase reference signal fd whose frequency is fx; and processing said phase difference to determine said time difference between said upstream and downstream travel times.

Claim 13

A method as in claim 10, wherein said test pulse trains are transmitted prior to measuring the rate of flow of said fluid.

Claim 14

A method as in claim 10, further comprising the steps of: grouping the variable frequencies of said test pulse trains into ranges; associating each of said ranges with a respective pair of transducers; and transmitting the test pulse trains with the range of frequencies which corresponds to said first and second transducers.

Claim 15

A method as in claim 12, wherein said frequencies are grouped into six ranges which are associated with six pairs of transducers.

Claim 16

A method as in claim 12, wherein a sweep frequency generator is used to generate said ranges of said variable-frequency pulse trains.

Claim 17

A method as in claim 12, wherein said ranges are derived from a master clock frequency

Claim 18

A method as in claim 15, wherein said phase relationship of said phase reference signal and said received signal is determined by counting clock pulses which are derived from a count clock frequency; and said master and count clock frequencies have a non-harmonic and non-pseudo-harmonic relationship.

Claim 19

A method as in claim 16, wherein the ratio of said count clock frequency to said master clock frequency is substantially about 0.65.

Claim 20

A method as in claim 17, wherein said ratio is substantially 0.650024.

Claim 21

A method as in claim 18, wherein said master clock frequency is substantially 41.6666 MHz and said count clock frequency is substantially 27.08 MHz.

Claim 22

A method as in claim 16, further comprising the step of electronically isolating the sources of the master and count clock frequencies from each other so as to prevent any synchronization thereof.

Claim 23

A method as in claim 10, further comprising the step of waiting until the received signal reaches a steady state before determining its amplitude.

Claim 24

An ultrasonic flow meter for measuring the rate of flow of a fluid within an enclosed axially elongated hollow conduit, comprising: first and second transducers securable to the exterior surface of said conduit, means for securing said first and second transducers spaced from each other along the axis of said conduit such that said first transducer is located downstream from said second transducer with respect to the direction of flow of said fluid; said transducers being capable of transmitting to each other, and receiving from each other, ultrasonic signals which pass through said fluid in said conduit; ultrasonic signal generation means for causing said first transducer to transmit a train of ultrasonic pulses in an upstream direction from said first to said second transducer and for causing said second transducer to transmit a train of ultrasonic pulses in a downstream direction from said second to said first transducer; means for determining the total transit time of said pulses in liquid between the transducers t L ; and flow measurement circuit means for measuring the rate of flow of said fluid as a function of the difference between the respective amounts of time said upstream and said downstream ultrasonic pulses take to travel between said transducers, and an overall time required for the ultrasonic signal to pass through the fluid during a single transmission between said first and second transducers; wherein said flow measurement circuit means determines said time difference by measuring phase differences between, on the one hand, said upstream ultrasonic pulse train received by said second transducer, and said downstream ultrasonic pulse train received by said first transducer; and on the other hand, a reference signal which is phase coherent with said transmitted ultrasonic signals; and wherein said flow measurement circuit means computes said flow rate in accordance with the following equation: V.sub.f =(K delta T)/t.sub.L wherein V f is a signal indicating the rate of flow of said fluid through said conduit, K is a proportionality constant, delta T is the difference between the upstream and downstream transmission times and t L is the overall time required for the ultrasonic signal to pass through the fluid during a single transmission between said first and second transducers.

Claim 25

An ultrasonic flow meter for measuring the rate of flow of a fluid within an enclosed axially elongated hollow conduit, comprising: first and second transducers securable to the exterior surface of said conduit, means for securing said first and second transducers spaced from each other along the axis of said conduit such that said first transducer is located downstream from said second transducer with respect to the direction of flow of said fluid; said transducers being capable of transmitting to each other, and receiving from each other, ultrasonic signals which pass through said fluid in said conduit; ultrasonic signal generation means for causing said first transducer to transmit a train of ultrasonic pulses in an upstream direction from said first to said second transducer and for causing said second transducer to transmit a train of ultrasonic pulses in a downstream direction from said second to said first transducer; means for determining the total transit time of said pulses in liquid between the transducers t L ; and flow measurement circuit means for measuring the rate of flow of said fluid as a function of the difference between the respective amounts of time said upstream and said downstream ultrasonic pulses take to travel between said transducers, and an overall time required for the ultrasonic signal to pass through the fluid during a single transmission between said first and second transducers; wherein said flow measurement circuit means determines said time difference by measuring phase differences between, on the one hand, said upstream ultrasonic pulse train received by said second transducer, and said downstream ultrasonic pulse train received by said first transducer; and on the other hand, a reference signal which is phase coherent with said transmitted ultrasonic signals; and wherein said flow measurement circuit means computes said flow rate in accordance with the following equation: V.sub.f =(K delta T)/t.sub.L wherein V f is a signal indicating the rate of flow of said fluid through said conduit, K is a proportionality constant, delta T is the difference between the upstream and downstream transmission times and t L is the overall time required for the ultrasonic signal to pass through the fluid during a single transmission between said first and second transducers.

Claim 26

A flow meter as in claim 22, wherein said flow measurement circuit means comprises detector means which receives signals Rx which are generated by said transducers in response to ultrasonic pulses received through said fluid; for digitizing a steady-state portion of said signal Rx to generate a digitized signal Rd.

Claim 27

A flow meter as in claim 22, wherein said flow measurement circuit means comprises a zero-crossover detector which receives signals Rx which are generated by said transducers in response to ultrasonic pulses received through said fluid, and which outputs a first digital value when Rx is substantially above zero and a second digital value when Rx is substantially below zero, to generate a digitized signal Rd.

Claim 28

A flow meter as in claim 24, further comprising means for supplying a digital demodulator clock signal fd whose frequency is fx and which is controlled to be remain approximately in quadrature with Rd; and XOR means for generating an up/down control signal which has a predetermined digital value when signals Rd and fd have a common digital value.

Claim 29

A flow meter as in claim 25, further comprising an up/down counter which receives said up/down control signal and also receives count clock pulses fc; and wherein said up/down counter counts up said count clock pulses when said up/down control signal has one of said digital values, and counts down when said up/down control signal has the other of said digital values; whereby, the total count of said up/down counter reflects the phase relationship of said signals Rd and fd.

Claim 30

A flow meter as in claim 26, further comprising separated means for generating said count clock pulses fc and said transmit frequency fx and for preventing synchronization thereof, said transmit and count clock frequencies having a non-harmonic and non-pseudo-harmonic relationship.

Claim 31

A flow meter as in claim 27, wherein the ratio of said count clock frequency to said transmit frequency is substantially about 0.65.

Claim 32

A method as in claim 28, wherein said ratio is substantially 0.650024.

Claim 33

A method as in claim 29, wherein said master clock frequency is substantially 41.6666 MHz and said count clock frequency is substantially 27.08 MHz.

Claim 34

A flow meter as in claim 27, wherein said separated means comprise respective circuits which are substantially isolated from one another.

Claim 35

An ultrasonic flow meter for measuring the rate of flow of a fluid within an enclosed axially elongated hollow conduit, comprising: first and second transducers securable to the exterior surface of said conduit; means for securing said first and second transducers spaced from each other along the axis of said conduit such that said first transducer is located downstream from said second transducer with respect to the direction of flow of said fluid; said transducers being capable of transmitting to each other, and receiving from each other, ultrasonic signals which pass through said fluid in said conduit; ultrasonic signal generation means for causing said first transducer to transmit a train of ultrasonic pulses in an upstream direction from said first to said second transdsucer and for causing said second transducer to transmit a train of ultrasonic pulses in a downstream direction from said second to said first transducer; and flow measurement circuit means for measuring the rate of flow of said fluid as a function of the difference between the respective amounts of time said upstream and said downstream ultrasonic pulses take to travel between said transducers; wherein said flow measurement circuit means determines said time difference by measuring phase differences between, on the one hand, said upstream ultrasonic pulse train received by said second transducer, and said downstream ultrasonic pulse train received by said first transducer; and on the other hand, a reference signal which is phase coherent with said transmitted ultrasonic signals; and wherein said signal generation means transmits a series of frequency test pulse trains having variable frequency, and said flow measurement circuit means determines which transmitted frequency results in the greatest amplitude signal received by the receiving transducer.

Claim 36

An ultrasonic flow meter for measuring the rate of flow of a fluid within an enclosed axially elongated hollow conduit, comprising: first and second transducers securable to the exterior surface of said conduit; means for securing said first and second transducers spaced from each other along the axis of said conduit such that said first transducer is located downstream from said second transducer with respect to the direction of flow of said fluid; said transducers being capable of transmitting to each other, and receiving from each other, ultrasonic signals which pass through said fluid in said conduit; ultrasonic signal generation means for causing said first transducer to transmit a train of ultrasonic pulses in an upstream direction from said first to said second transdsucer and for causing said second transducer to transmit a train of ultrasonic pulses in a downstream direction from said second to said first transducer; and flow measurement circuit means for measuring the rate of flow of said fluid as a function of the difference between the respective amounts of time said upstream and said downstream ultrasonic pulses take to travel between said transducers; wherein said flow measurement circuit means determines said time difference by measuring phase differences between, on the one hand, said upstream ultrasonic pulse train received by said second transducer, and said downstream ultrasonic pulse train received by said first transducer; and on the other hand, a reference signal which is phase coherent with said transmitted ultrasonic signals; and wherein said signal generation means transmits a series of frequency test pulse trains having variable frequency, and said flow measurement circuit means determines which transmitted frequency results in the greatest amplitude signal received by the receiving transducer.