Chordal gas flowmeter with transducers installed outside the pressure boundary

1. A flowmeter for detecting gas flow rates in a pipe comprising:

a container configured to be attached to the pipe having a channel through which the gas flows, and a plurality of recesses, each recess having a window made of titanium that is in acoustic communication with the channel;

a plurality of transducers, with one transducer of the plurality of transducers disposed in each recess, the transducers transmitting ultrasonic signals into and receiving ultrasonic signals from the channel through the window in the recess in which a transducer is disposed; and

a controller in electrical communication with the plurality of transducers which determines the gas flow rate through the channel from signals received from the transducers.

2. The flowmeter as described in claim 1 wherein the window has a thickness less than ¼ wavelength of the window's material.

3. The flowmeter as described in claim 2 wherein the window thickness is about 3 mm of the window's material.

4. The flowmeter as described in claim 3 including transducer housings disposed in the recesses that extend through the pipe container in which the transducers are disposed.

5. The flowmeter as described in claim 4 wherein the window is a pressure boundary which contains the pressure in the channel and essentially prevents gas in the channel from escaping into the housing, the window forming a gas tight seal with the channel.

6. The flowmeter as described in claim 5 wherein the transducers can be removed from the recesses without having to depressurize the pipe.

7. The flowmeter as described in claim 6 wherein the ultrasonic signals transmitted and received by the transducers define a first path in a first plane and a second path in a second plane which cross in the channel.

8. The flowmeter as described in claim 7 including acoustic isolators which acoustically isolate the transducer housings from the pipe container.

9. The flowmeter as described in claim 8 wherein the transducer couples to the window.

10. The flowmeter as described in claim 9 including a spring assembly disposed in each housing which applies a force against the transducer to hold the transducer in contact with the window.

11. The flowmeter as described in claim 10 including a plurality of transformers, with each transducer in electrical communication with one of the plurality of transformers.

12. The flowmeter as described in claim 11 wherein each path of each plane includes an upstream ultrasonic transducer and a downstream ultrasonic transducer configured so plane waves generated by the downstream transducer propagate through the channel and are received by the upstream transducer which produces an upstream transducer signal, and plane waves generated by the upstream transducer propagates through the channel and are received by the downstream transducer which produces a downstream transducer signal, the controller determining the gas flow rate from the upstream transducer signal and the downstream transducer signal.

13. The flowmeter as described in claim 12 wherein each transducer is a broad band piezoelectric composite transducer with a coupling coefficient greater than 0.7 out of 1 and an acoustic impedance of less than 34 Mrayls.

14. A method for detecting gas flow rates in a pipe comprising the steps of:

transmitting ultrasonic signals from a plurality of transducers disposed in recesses in a container attached to the pipe through a window made of titanium of each recess into a channel of the container in which the gas flows, with one transducer of the plurality of transducers disposed in each recess and the window in acoustic communication with the channel;

receiving ultrasonic signals from the channel through the windows by the transducers in the recesses; and

determining the gas flow rate through the channel from signals received from the transducers by a controller in electrical communication with the plurality of transducers.

15. The method as described in claim 14 wherein the window is a pressure boundary which contains the pressure in the channel and essentially prevents gas in the channel from escaping into the housing, the window forming a gas tight seal with the channel and there is the step of removing one of the transducers from the recess the one transducer in which the transducer is disposed without having to depressurize the pipe.

16. The method as described in claim 15 wherein the transmitting step includes the step of transmitting ultrasonic signals by the transducers along a first path in a first plane and a second path in a second plane which cross in the channel and the receiving step includes the step of receiving ultrasonic signals by the transducers from the first path and from the second path.

17. The method as described in claim 16 including the step of acoustically isolating housings in which the transducers are disposed in the recesses from the container with acoustic isolators.

18. The method as described in claim 17 including the step of applying a force against the transducer to hold the transducer in contact with the window.

19. The method as described in claim 18 wherein the transmitting step includes the steps of:

generating with an upstream ultrasonic transducer of the first path plane waves that propagate through the channel and are received by a downstream ultrasonic transducer of the first path;

producing a downstream transducer signal with the downstream transducer from the plane waves the downstream transducer receives;

generating with the downstream ultrasonic transducer of the first path plane waves that propagate through the channel and are received by the upstream ultrasonic transducer of the first path;

producing an upstream transducer signal with the upstream transducer from the plane waves the upstream transducer receives; and

determining with the controller the gas flow rate from the upstream transducer signal and the downstream transducer signal.