Flow meter with ultrasound transducer directly connected to and fixed to measurement circuit board

Abstract

An ultrasound flow meter unit arranged to measure a fluid flow rate with one or more ultrasound transducers (606), and a circuit board (602) with an electronic circuit arranged to operate the ultrasound transducer(s) (106, 306). The ultrasound transducer (606), e.g. in the form of a piezo-electric element, is mechanically fixed to the circuit board (602) by a first electrically conducting fixing means which additionally serve(s) to provide an electrical connection between an electrical terminal of the transducer (606) and the electronic circuit. Hereby a functional flow measurement unit (600) is provided which can be tested prior to assembly with a flow meter housing etc. Preferably, a set of ultrasound transducers (106, 306) are soldered directly onto electrically conducting paths (631) on a surface of the circuit board (602) being in electrical connection with the electronic circuit, e.g. in a single SMT mounting process together with mounting of all other electronic components on the circuit board (602). Through-going openings (630, 640) of the circuit board (602) in the vicinity of these conducting paths (631) serve to provide thermal elasticity. A metal clip soldered to the circuit board (602) may serve to electrically connect a second electrical terminal of the transducer (606) to the electronic circuit.

Claims

1. An ultrasound flow meter unit arranged to measure a fluid flow rate, the unit comprising: a first ultrasound transducer having a first and a second electrical terminal, and a circuit board with an electronic circuit arranged thereon for operating the first ultrasound transducer, wherein the circuit board comprises a first conducting path electrically connected to the first electrical terminal.[.,.]. and to the electronic circuit, wherein the .Iadd.first .Iaddend.ultrasound transducer .[.is.]. .Iadd.includes .Iaddend.a monolithic body of piezo-electric material .[.with.]. .Iadd.and has .Iaddend.one surface in contact with a surface of the circuit board, and .[.wherein the monolithic body is mechanically fixed to the circuit board by a first electrically conducting fixing means, which provides the electrical connection between the first electrical terminal and the first conducting path.]. .Iadd.wherein the first ultrasound transducer is mounted on top of a through-going hole of the circuit board and surface mounted to the circuit board by fixing the first conducting path arranged at least partially around a periphery of the through-going hole of the circuit board to the first electrical terminal arranged on a periphery of the one surface of the first ultrasound transducer in contact with the circuit board.Iaddend..

2. The ultrasound flow meter unit according to claim 1, wherein the .[.first fixing means comprises.]. .Iadd.the first conducting path is fixed to the first electrical terminal by using .Iaddend.at least one of: solder.[.,.]. .Iadd.or .Iaddend.electrically conducting glue.[., or an electrically conducting clip.]..

3. The ultrasound flow meter unit according to claim 1, wherein the .[.circuit board has one or more.]. through-going .[.openings.]. .Iadd.hole is .Iaddend.partly or entirely covered by the first ultrasound transducer when fixed to the circuit board.

.[.4. The ultrasound flow meter unit according to claim 3, wherein a part of the first conducting path is arranged in the vicinity of at least one of the through-going opening(s) in the circuit board..].

.[.5. The ultrasound flow meter unit according to claim 1, wherein the ultrasound transducer is mounted on top of a through-going hole of the circuit board or on top of a non through-going cavity of the circuit board..].

6. The ultrasound flow meter unit according to claim .[.4.]. .Iadd.1.Iaddend., wherein the .[.monolithic body.]. .Iadd.first ultrasound transducer .Iaddend.is fixed to the circuit board by soldering the first conducting path to the first electrical terminal .[.on a periphery of the end part of the ultrasound transducer facing the circuit board.]..

7. The ultrasound flow meter unit according to claim .[.5.]. .Iadd.1.Iaddend., wherein .[.a.]. .Iadd.the .Iaddend.through-going .[.opening.]. .Iadd.hole .Iaddend.is accompanied by openings positioned outside the area covered by the first ultrasound transducer when fixed to the circuit board.

8. The ultrasound flow meter unit according to claim 7, wherein .[.a.]. .Iadd.the .Iaddend.through-going .[.opening in the form of.]. .Iadd.hole is .Iaddend.a circular hole surrounded by a circular conducting path.[.,.]. .Iadd.and .Iaddend.is accompanied by four narrow through-going openings outside the area with the circular conductive path.

9. The ultrasound flow meter unit according to claim 7, wherein .Iadd.the first conducting path includes .Iaddend.a generally annular conductor with a cut .[.serves.]. for connection to the first terminal of the .Iadd.first .Iaddend.ultrasound transducer, and wherein .[.a.]. .Iadd.the .Iaddend.through-going .[.opening.]. .Iadd.hole .Iaddend.is arranged inside the conductor and a through-going .[.grove.]. .Iadd.groove .Iaddend.is arranged outside the conductor.

10. The ultrasound flow meter unit according to claim 7, wherein .Iadd.the first conducting path includes .Iaddend.an annular conductor .[.serves.]. for connection to the first terminal of the .Iadd.first .Iaddend.ultrasound transducer, and wherein .[.a.]. .Iadd.the .Iaddend.through-going .[.opening.]. .Iadd.hole .Iaddend.is arranged inside the conductor and a through-going .[.grove.]. .Iadd.groove .Iaddend.is arranged outside the conductor.

11. The ultrasound flow meter unit according to claim 1, wherein a second conducting path on the surface of the circuit board serves to electrically connect the electronic circuit .[.with.]. .Iadd.to .Iaddend.the second electrical terminal of the first ultrasound transducer.

12. The ultrasound flow meter unit according to claim 11, wherein a metal clip serves to electrically connect the second conducting path to the second electrical terminal of the first ultrasound transducer.

13. The ultrasound flow meter unit according to claim 11, wherein the second conducting path is placed within the first conducting path and separated by a through-going opening.

14. The ultrasound flow meter unit according to claim 1, wherein the ultrasound flow meter further comprises a second ultrasound transducer, wherein the electronic circuit is further arranged for operating the second ultrasound transducer, wherein the second ultrasound transducer is mechanically fixed to the circuit board .[.by a second electrically conducting fixing means, which additionally serve(s).]. to provide an electrical connection between at least one electrical terminal of the second ultrasound transducer and the electronic circuit, and wherein both of the first and second ultrasound transducers are mechanically fixed to the same side of the circuit board.

15. The ultrasound flow meter unit according to claim 14, comprising a substantially watertight membrane arranged around the circuit board and the first and second ultrasound transducers, and wherein a plug with a plurality of electrical terminals penetrates through the membrane so as to allow external connection to the electronic circuit, wherein at least a part of the membrane is electrically conducting and serves to electrically connect the second electrical terminal of the first ultrasound transducer with a second electrical terminal of the second ultrasound transducer.

16. A flow meter arranged to measure a flow rate of a fluid flowing through a measuring tube, wherein the flow meter comprises: a housing with the measuring tube arranged inside, and an ultrasound flow meter unit according to claim 1 arranged in relation to the housing.

17. The flow meter according to claim 16, wherein said flow meter is a heat meter, a cooling meter, a water meter, or a gas meter.

.Iadd.18. An ultrasound flow meter unit arranged to measure a fluid flow rate, the unit comprising: a first ultrasound transducer including a monolithic body of piezo-electric material and having a first and a second electrical terminal; a circuit board with an electronic circuit arranged thereon for operating the first ultrasound transducer; wherein the first ultrasound transducer is electrically and mechanically connected to the circuit board by connecting one of the first and second electric terminal to an at least partially annular conductive path of the circuit board having outside thereof at least one through-going opening or groove to effectively absorb extensions and contractions of the piezo-electric material..Iaddend.

.Iadd.19. The ultrasound flow meter unit of claim 18, wherein the first ultrasound transducer has a cylindrical shape with a first end surface with a first periphery and a second end surface with a second periphery, wherein the first end surface faces the circuit board..Iaddend.

.Iadd.20. The ultrasound flow meter unit of claim 19, wherein the at least partially annular conductive path of the circuit board is at least partially surrounded by a void formed in the circuit board..Iaddend.

.Iadd.21. The ultrasound flow meter unit of claim 20, wherein the void at least partially surrounds the first periphery of the first ultrasound transducer..Iaddend.

.Iadd.22. The ultrasound flow meter unit of claim 18, wherein the ultrasound flow meter unit comprises a second ultrasound transducer..Iaddend.

.Iadd.23. The ultrasound flow meter unit of claim 22, wherein the second ultrasound transducer includes an additional monolithic body of piezo-electric material and having a third and a fourth electrical terminal; wherein the electronic circuit is arranged for operating the second ultrasound transducer; wherein the second ultrasound transducer is electrically connected to the electronic circuit arranged on the circuit board via the third and fourth electrical terminals, and wherein the second ultrasound transducer is mechanically connected to the electronic circuit arranged on the circuit board by a second at least partially annular conductive path of the circuit board having outside thereof at least one second through-going opening or groove to effectively absorb extensions and contractions of the piezo-electric material of the second ultrasound transducer..Iaddend.

.Iadd.24. The ultrasound flow meter unit of claim 23, wherein the second ultrasound transducer has a cylindrical shape with a third end surface with a third periphery and a fourth end surface with a fourth periphery, the third end surface facing the circuit board, wherein the second ultrasound transducer is mechanically fixed onto a surface of the second at least partially annular conductive path of the circuit board, wherein the second at least partially annular conductive path of the circuit board is arranged along the third periphery of the second ultrasound transducer; and wherein the second at least partially annular conductive path of the circuit board is at least partially surrounded by a second void formed in the circuit board..Iaddend.

.Iadd.25. The ultrasound flow meter unit of claim 24, wherein the second void at least partially surrounds the third periphery of the second ultrasound transducer..Iaddend.

.Iadd.26. A flow meter arranged to measure a flow rate of a fluid flowing through a measuring tube, wherein the flow meter comprises: a housing with the measuring tube arranged inside, and an ultrasound flow meter unit according to claim 18 arranged in relation to the housing..Iaddend.

.Iadd.27. The flow meter according to claim 26, wherein said flow meter is a heat meter, a cooling meter, a water meter, or a gas meter..Iaddend.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

(2) FIGS. 1a and 1b illustrate a mechanically separate unit comprising a circuit board and two ultrasound transducers mounted outside a plane of the circuit board in an assembled and in a pre-assembly state, respectively,

(3) FIGS. 2a and 2b illustrate a circuit board and ultrasound transducers before and after assembly into a mechanically separate part consisting of circuit board and ultrasound transducers mounted in an SMT process,

(4) FIG. 3 illustrates an ultrasound flow meter with a flow meter housing made of metal and a mechanically separate unit comprising a circuit board and two ultrasound transducers,

(5) FIG. 4 illustrates an ultrasound flow meter with a flow meter housing made of polymer and a mechanically separate part comprising a circuit board and two ultrasound transducers, and

(6) FIGS. 5a and 5b illustrate one SMT embodiment with an annular conducting path arranged around a central hole in the circuit board,

(7) FIGS. 6a and 6b illustrate another SMT embodiment similar to the one of FIG. 5, but with additional through-going openings outside the annular conducting path,

(8) FIG. 7 illustrates yet another SMT embodiment, where a generally annular conducting path is arranged within one through-going opening surrounding the annular conducting path, but where the annular conductor and the underlying circuit board part has a cut so as to better allow for thermal movement during manufacturing,

(9) FIGS. 8a and 8b illustrate an SMT embodiment, where an annular conducting path connects to first transducer terminal, while another conductor on the circuit board connects to a metal clip that serves to connect to a second transducer terminal, and

(10) FIGS. 9a and 9b illustrate an SMT embodiment with conducting pads arranged for soldering to respective concentrically positioned electrical terminals of the ultrasound transducer, thus allowing the transducer to be fully SMT mounted to the circuit board.

DESCRIPTION OF EMBODIMENTS

(11) FIG. 1a shows a mechanically separate unit 100 comprising a plane single or multi-layer circuit board 102 with an electronic circuit 104, such as implemented with SMT mounted components, and with cylindrically shaped piezoelectric ultrasound transducers 106 mounted spaced apart and outside a plane defined by the circuit board 102, namely on a surface of the circuit board 102. The ultrasound transducers 106 in the shown embodiment are mounted on top of respective through-going holes of the circuit board 102, however, other embodiments could have cavities which are not through-going, or have planar surfaces without holes. The ultrasound transducers 106 are arranged for radiating ultrasonic signals perpendicular to a plane defined by the circuit board 102.

(12) The electronic circuit 104 is arranged to control the operation of the ultrasound transducers 106 and thus perform ultrasound flow measurements. The electronic circuit 104 may provide an electric output signal in the form of electric pulses with a rate corresponding to the measured flow rate, and/or the electronic circuit 104 may be arranged to output data representing a measured amount of flow, such as by means of a digital electric signal, e.g. on a single wire.

(13) Metallic clips 110 serve as fixing members for fixing a position of the ultrasound transducers 106 and for providing electrical connection to the electronic circuit 104 on the circuit board 102. The metal clips 110 may be SMT soldered to conductive paths on the circuit board 102, however the clips 110 may also be attached to the circuit board by other means such as conductive glue, by means of a screw through the circuit board 102 or the like. Depending on the location of the electrical terminals on the ultrasound transducer 106, the two clips 110 shown for each transducer 106 may either only serve to electrically connect one electrical terminal to the circuit board, or the two clips 110 may serve to electrically connect respective first and second electrical terminals of the ultrasound transducer 106.

(14) The unit 100 including circuit board 102 and transducers 106 can be electrically connected and tested in a test-stand before being mounted on a housing with a measuring tube inside and thus before final assembly of the flow meter.

(15) The unit 100 can be used for mounting on flow meter housings with or without through-going openings to the fluid medium to be measured on. However, in preferred embodiments, the 100 according to the invention is combined with a housing without such through-going opening, i.e. based on transmission of ultrasound signals through the material of the housing according to the so-called matching layer principle. E.g. the housing may be a polymeric housing.

(16) FIG. 1b shows a perspective view of a circuit board 102 as in FIG. 1a, but prior to mounting the ultrasound transducers 106 in relation to the circuit board 102. The clips 110 may be SMT mounted on the circuit board 102 in the same process as the electronic components of the electronic circuit 504, and subsequently the ultrasound transducers 106 are locked into place and electrically connected by means of the clips 110.

(17) As seen, the ultrasound transducers 106 are mounted over respective through-going holes 108 of the circuit board, hereby allowing a contact force to be applied on each of the ultrasound transducers 106, through the plane of the circuit board 102, without applying the force through the material of the circuit board 102.

(18) FIG. 2a shows two ultrasound transducers 206 and a circuit board 202 with an electronic circuit 204 prior to fixing the transducers on the circuit board in an SMD process. In a preferred embodiment suited for SMT fixing of the transducers 206, the circuit board 502 is provided with though-going holes 208 with a circular shape having a diameter smaller than the circular transducers 206, and the holes 208 are placed such that the transducers 206, when mounted, cover the holes 208. However, other embodiments may have cavities, which are not through-going, or plane surfaces without holes or cavities.

(19) FIG. 2b shows a mechanically separate unit 200 comprising a circuit board 202 with an electronic circuit 204 and two ultrasound transducers 206, where the transducers 206 are fixed on the circuit board 202 in an SMT process. Solder between the circuit board 202 and each of the transducers 206 serves to mechanically fix the transducers 206 to the circuit board 202. Furthermore, the electrically conducting solder connects each of the transducers 206 electrically to the electronic circuit 204.

(20) FIG. 3 shows a perspective view of an ultrasound flow meter with a metallic or polymeric flow meter housing 320, with a measuring tube 314 adapted for fluid flow inside, and a mechanically separate part comprising a circuit board 302 with an electronic circuit 304 and two piezoelectric ultrasound transducers 306. The mechanically separate unit comprising the transducers 306 and the circuit board 302 is fixed to the housing 320 with bracings 316 in order to ensure that enough force is applied to the transducers in the direction towards a centre line of the measuring tube in the housing in order to counteract the force applied in the opposite direction from the pressure of the fluid inside the housing during operation. Each end of the flow meter housing 320 is provided with threading 318 in order to facilitate mounting onto adjacent pipelines. The electronic circuit 304 is provided with external connections in the form of pins enabling the electrical connection to other electronic circuits, such as calculator units, power supplies and telecommunication units. Alternatively, a wireless connection could be used.

(21) FIG. 4 shows a perspective view of an ultrasound flow meter with a polymeric flow meter housing 420, with a through-going opening 414 adapted for fluid flow and with a measuring tube arranged inside, and a mechanically separate part comprising a circuit board with an electronic circuit 404 and piezoelectric ultrasound transducers. The polymeric flow meter housing 420 is monolithically formed in a die casting process and is enclosing a cavity suited for containing components, such as the electronic circuit 404. This cavity is separated from the through-going opening 414 by a wall, and the ultrasound transducers on the circuit board transmit ultrasound signals through this wall and thus operates according to the so-called matching layer principle. The mechanically separate unit comprising the transducers and the circuit board is clamped to the housing 420 with bracing 416. Each end of the flow meter housing is provided with threading 418 in order to facilitate mounting onto adjacent pipelines. The electronic circuit 404 is provided with external connections in the form of pins enabling the electrical connection to other electronic circuits, such as calculator units, power supplies and telecommunication units. Alternatively, a wireless connection could be used. The shown embodiment can be used as a consumption meter, such as a water meter, a heat meter or a cooling meter.

(22) FIGS. 5a and 5b, shows a circuit board 502 embodiment in the form of a unit 500 which can be tested separately, in a pre-assembly state and in an assembled state, respectively. In FIG. 5a a magnified view of the circuit board 502 is included to better show the conductive path 531 arranged around the through-going opening 530 below the ultrasound transducers 506. The shown embodiment is suited for SMT mounting, such as SMT mounting of all electronic components of the measurement circuit 504 and the ultrasound transducers 506 in one SMT mounting process where all components are soldered directly to the circuit board 502. After SMT mounting, the unit 500 is prepared for functional testing, since it can be connected in a test setup via the electrical terminals 550, i.e. the same terminals which are used for electrical connection in the final flow meter or consumption meter, such as connection to a calculator unit. Alternatively, electrically conductive glue may be used to fix and connect the ultrasound transducers 506 to the conductive paths 531 of the circuit board 502.

(23) As seen, the circuit board 502 is plane in its entire extension, and in principle the circuit board 502 may be a simple standard type one, two or more layer circuit board. The holes 530, and the conductive paths 531 around the circular holes 530, serve to determine a position of the ultrasound transducers 506, and thus a distance between the two ultrasound transducers 506 in the final flow meter. Therefore, a distance between the holes 530 in the circuit board 502 should be selected to corresponding transducer positions of the flow meter housing, and also a corresponding distance between ultrasound reflectors serving to reflect ultrasound between the two ultrasound transducers 506. Using SMT mounting of the ultrasound transducers 506, preferably in an automated production line, it is possible to very precisely position the two ultrasound transducers 506 in relation to each other, and thereby provide a good fit to the flow meter housing.

(24) In the shown embodiment on FIGS. 5a, 5b, the ultrasound transducers 506 are in the form of cylindrically shaped piezoelectric elements with plane end parts. The two electrical terminals of the ultrasound transducers 506 are placed on the opposite end parts, one facing the circuit board 502, and one facing away from the circuit board 502. The two electrical terminals may either be the entire end parts or may be only part of the end parts, especially the peripheral part. In the shown example, the conductive path 531 is suited for soldering to the electrical terminal on a periphery of the end part of the ultrasound transducer 506 facing the circuit board 502. The other electrical terminal on the end part of the ultrasound transducer 506 facing away from the circuit board 502 may be connected to the measurement circuit 504 by other means, e.g. using wires soldered to the electrical terminals. Alternatively, an electrically conductive membrane covering both transducers may be used to establish electrical connection between the electrical terminals facing away from the circuit board 502 of both transducers 506, and wherein this electrically conductive membrane is connected to the electronic circuit 504 e.g. by means of a wire soldered to the membrane.

(25) FIGS. 6a and 6b shows a variant of the circuit board of FIGS. 5a and 5b. A testable unit 600 comprising ultrasound transducers 606 in the form of cylindrically shaped piezoelectric element, and a circuit board 602 with measurement electronics 604 serving to operate the ultrasound transducers 606 is provided, preferably by means of an automated SMT process, where all electronic components and the ultrasound transducers 606 are directly soldered to conductive paths of the circuit board 602.

(26) In the magnified view, the circuit board 602 area where the ultrasound transducer 606 is mounted has a circular conductive path 631 suited for connection to one electrical terminal of the ultrasound transducer 606. A through-going opening in the form of a circular hole 603 is in this embodiment accompanied by four narrow through-going openings 640 outside the area with the circular conductive path 631. These openings 640 serve to facilitate adaptation to extensions and contractions of the piezo-electric elements 606. As seen, the piezo-electric elements 606 cover the holes 630, when mounted, whereas the openings 640 are positioned outside the area covered by the piezo-electric elements 606.

(27) FIG. 7 illustrates a variant of the circuit board of FIGS. 6a and 6b. In FIG. 7, a generally annular conductor 731 serves for connection to one terminal of the piezo-electric element. A through-going hole 730 inside the conductor 731 and a through-going groove 740 outside the conductor 731, together with a cut 732 in the conductor 731 and the underlying part of the circuit board 702, these holes and grooves serve to effectively absorb extensions and contractions of the piezo-electric elements 706.

(28) FIGS. 8a and 8b illustrate another circuit board 802 variant, where both electrical terminals of the piezo-electric elements 806 are connected to the circuit board 802, again providing a complete flow measurement unit 800 prepared for testing. An annular conductor 831 on a surface of the circuit board is arranged for soldering to a first electrical terminal of the piezo-electric element 806. This conductor 831 has in its vicinity a central through-going hole 830, and around its periphery a through-going groove 840, with the same effect as mentioned for the embodiment of FIG. 7. However, in this embodiment, another conductor 832 on the surface of the circuit board 802 is arranged for soldering to a metal clip 810, i.e. a piece of metal bend into shape. This conductor 832 is positioned outside a periphery of the circular piezo-electric element 806 when placed in its intended position on the circuit board. The metal clip 810 can then be soldered to the conductor 832 in the same SMT process as fixing and electrically connecting the piezo-electric element 806 to the conductor 831. However, the metal clip 810 may alternatively be soldered or conductively glued to the conductor 832 manually after SMT mounting of the other electrical components.

(29) As seen, the metal clip 810 is bent into shape so as to provide electrical contact to a peripheral part of the side of the piezo-electric element 806 facing away from the circuit board, i.e. to the second electrical terminal of the piezoelectric element 806. An advantage of this type of electrical connection of the electronic circuit to the piezo-electric element 806 is that it is suited for being carried out in one single automated SMT mounting process, since the bent metal clip 810 is not mechanically supported by the piezo-electric element 806 during the SMT process, and thus the piezo-electric element and thus the metal clip 810 is not prevented from proper mechanical contact with the solder and the electric path on the circuit board 802 during the SMT process, which may otherwise lead to a poor electrical connection between the metal clip 810 and the electronic circuit on the circuit board 802. In this case electrical contact will be established when the unit 800 is mounted on a housing, since here the metal clip 810 will be pressed against a surface of the housing, thus causing the metal clip 801 to touch the electrical terminal of the piezo-electric element 806. However, it is to be understood that the metal clip 810 may also be shaped to provide immediate contact to the piezo-electric element 806, when soldered or fixed to the conductor 832, without any external force, if preferred.

(30) The combination of directly soldering one electrical terminal of the piezo-electric element 806 to the circuit board 802 and connecting a second electrical terminal via a metal clip soldered to the circuit board 802 is advantageous, since full electrical connection of the piezo-electric element 806 can be established in one single SMT mounting process, if preferred.

(31) FIGS. 9a and 9b illustrate a circuit board 902 variant suited for ultrasound transducers 906 in the form of circular piezoelectric elements 906 with both electrical terminals 907, 909 placed on a surface of one plane side, and thus suited for direct soldering to respective conductors 931, 933 on a surface of the circuit board 902. In FIG. 9a the circuit board 902 is seen from the component side, while FIG. 9b illustrates the opposite side of the circuit board 902 where the external electrical terminal 950 of the flow measurement unit is visible, here illustrated as a 6-pin plug, however external interfaces with fewer or more electrical terminals may be preferred. In embodiments with an on-board battery, such external interface may be purely wireless.

(32) In the illustrated variant, the two electrical terminals 907, 909 are concentrically arranged on one surface of the piezoelectric element 906. The first electrical terminal 907 has an annular shape and is arranged on a peripheral part of the plane surface of the piezo-electric element 906, while the second electrical terminal 909 is positioned in a central part of the surface, inside the first terminals 907. The conductor 933 is placed within the conductor 931 and separated by a through-going opening 930. Outside the conductor 931, a through-going opening 940 is also provided, with the same effect as previously mentioned.

(33) The magnified view illustrates the corresponding first conductor 931 on the surface board has an annular shape suited to fit the shape of the first terminal 907, while the second conductor 933 is positioned inside the annular first conductor 931 so as to fit the position of the second terminal 909.

(34) The embodiment illustrated in FIGS. 9a and 9b is advantageous since it allows full electrical connection of the ultrasound transducer 906 to the circuit board 902 in one single SMT mounting process without involving further components than solder. However, the illustrated transducer type 906 requires the correct side of the transducer 906 to face the circuit board 902 in order to work. However, if this is taken into account, the mechanical fixing and electrical connection of the transducer 906 can be combined in an elegant way in one single SMT process.

(35) It is to be understood that the details of the arrangement of the electrically conductive portions on the circuit boards illustrated in FIGS. 5-9 may be combined in any way to provide a desired configuration, depending on the selected type of ultrasound transducer.

(36) The invention provides a highly versatile stand-alone unit for a large variety of applications where a flow rate of a fluid is to be measured. A simple electrical interface can be provided, e.g. where the measured flow rate is output as pulses. This interface may be reduced down to one single electrical pin, see e.g. European patent application publication No. EP 2 042 837, e.g. with part of the casing being a metal serving as electrical ground connector. Hereby, the unit is easy to fit into different applications. In some embodiments, a battery is provided within the water-tight casing, thus allowing a completely self-contained flow meter unit with a simple electric interface.

(37) Further, the range of applications is extended due to the rather compact size of the unit, especially in versions where the electronic circuit is refined to allow a high measurement accuracy with a limited distance between the first and second ultrasound transducers, e.g. as described in European patent application EP 2 339 301. This means that the unit can be used in applications where only a limited space is available for the flow rate sensor.

(38) Examples of relevant applications are: consumption meters for charging purposes, measurement of blood flow in medical examination or surveillance, ingredient flow within the food industry, flow of water, air or fuel in a machinery (e.g. a vehicle), flow provided to single sources or groups of heating/cooling elements (or the related heating/cooling power based on measurement of the flow) as feedback to heating/cooling control systems.

(39) In all cases, such applications can profit from high precision fluid flow measurements which can be provided at low cost since the flow meter is suited for full or at least highly automated mass production.

(40) To sum up the invention provides an ultrasound flow meter unit arranged to measure a fluid flow rate with one or more ultrasound transducers (606), and a circuit board (602) with an electronic circuit arranged to operate the ultrasound transducer(s) (106, 306). The ultrasound transducer (606), e.g. in the form of a piezo-electric element, is mechanically fixed to the circuit board (602) by a first electrically conducting fixing means which additionally serve(s) to provide an electrical connection between an electrical terminal of the transducer (606) and the electronic circuit. Hereby a functional flow measurement unit (600) is provided which can be tested prior to assembly with a flow meter housing etc. Preferably, a set of ultrasound transducers (106, 306) are soldered directly onto electrically conducting paths (631) on a surface of the circuit board (602) being in electrical connection with the electronic circuit, e.g. in a single SMT mounting process together with mounting of all other electronic components on the circuit board (602). Through-going openings (630, 640) of the circuit board (602) in the vicinity of these conducting paths (631) serve to provide thermal elasticity. A metal clip soldered to the circuit board (602) may serve to electrically connect a second electrical terminal of the transducer (606) to the electronic circuit.

(41) In the following, embodiments E1-E18 describe additional possible embodiments of the invention.

(42) E1. An ultrasound flow meter arranged to measure a flow rate of a fluid flowing through a measuring tube, the flow meter comprising a housing (620) with the measuring tube (614) arranged inside, and a mechanically separate unit (100, 300) arranged in relation to the housing, the mechanically separate unit (100, 300) comprising at least one ultrasound transducer (106, 306), and a circuit board (102, 302) with an electronic circuit (104, 304) arranged for operating the at least one ultrasound transducer (106, 306), wherein at least one fixing member (110, 310) is attached to the circuit board (102, 302), wherein the fixing member (110, 310) serves to limit relative movement between the circuit board (102, 302) and the ultrasound transducer (106, 306), such as the fixing member (110, 310) serving to fix the ultrasound transducer (106, 306) to the circuit board (110, 310).

(43) E2. Ultrasound flow meter according to E1, wherein the ultrasound transducer (106, 306) is kept in position by the fixing member (110, 310) outside a plane defined by the circuit board (102, 302, such as on a surface of the circuit board (102, 302).

(44) E3. Ultrasound flow meter according to E1, wherein the circuit board (102, 302) comprises an edge (108, 308) shaped to fit at least a part of the ultrasound transducer (106, 306), and wherein the ultrasound transducer (106, 306) is kept in position by the fixing member (110, 310) such that a plane defined by the circuit board (102, 302) intersects through the ultrasound transducer (106, 306), when mounted for normal operation.

(45) E4. Ultrasound flow meter according to E3, wherein said edge (108, 308) of the circuit board serves, together with the fixing member (110, 310), to fix the position of the ultrasound transducer (106, 306) in relation to the circuit board (102, 302).

(46) E5. Ultrasound flow meter according to E3 or E4, wherein said edge is an edge of a through-going hole (108, 308) through the circuit board (102, 302), wherein the through-going hole (108, 308) is shaped to fit a size of the ultrasound transducer (106, 306).

(47) E6. Ultrasound flow meter according to any of E1-E5, wherein the fixing member (110, 310) comprises an electrically conductive portion, and wherein this electrically conductive portion serves to electrically connect the circuit board (102, 302) and the ultrasound transducer (106, 306).

(48) E7. Ultrasound flow meter according to E6, wherein separate first and second parts of the fixing member (110, 310) serve to provide respective first and second electrical connections between the ultrasound transducer (106, 306) and the circuit board (102, 302).

(49) E8. Ultrasound flow meter according to any of E1-E7, wherein the fixing member (110, 310) comprises one or more clips attached to the circuit board (102, 302), such as one or more metal clips.

(50) E9. Ultrasound flow meter according to any of E1-E8, wherein the fixing member (110, 310) comprises one or more solderings serving to attach the ultrasound transducer (106, 306) to the circuit board (102, 302).

(51) E10. Ultrasound flow meter according to any of E1-E9, comprising first and second ultrasound transducers (106, 306) fixed to the circuit board (102, 302) by respective first and second parts of the fixing member (110, 310).

(52) E11. Ultrasound flow meter according to E10, wherein the circuit board (302) and the fixing member (310) serve to fix the first and second ultrasound transducers (306) in position relative to each other, and wherein a distance (722) between the first and second ultrasound transducers (306) matches a distance (724) between corresponding first and second transducer receiving positions of the housing (620).

(53) E12. Ultrasound flow meter according to any of E1-E11, wherein the housing (620, 820) is formed by metal, such as brass or stainless steel, or by a polymeric material.

(54) E13. Consumption meter comprising a flow meter according to any of E1-E12, wherein the consumption meter is one of: a heating meter, a cooling meter, a water meter, or a gas meter.

(55) E14. A method of manufacturing an ultrasound flow meter, the method comprising forming a mechanically separate unit comprising an ultrasound transducer and a circuit board with an electronic circuit used for controlling the ultrasound transducer by mounting the ultrasound transducer relative to the circuit board by means of a fixing member serving to limit relative movement between the ultrasound transducer and the circuit board, and mounting the mechanically separate unit to a housing arranged for fluid flow.

(56) E15. Method according to claim E14, comprising mounting the ultrasound transducer to the circuit board by means of one or more clips, such as metal clips.

(57) E16. Method according to E14 or E15, comprising soldering the ultrasound transducer to the circuit board, such as by means of a Surface Mounting soldering process.

(58) E17. Method according to any of E14-E16, comprising a step of testing a function of the mechanically separate unit prior to mounting the mechanically separate unit to the housing arranged for fluid flow.

(59) E18. Method according to any of E14-E17, comprising mounting first and second ultrasound transducers relative to the circuit board by means of respective first and second parts of the fixing member.

(60) Although the present invention has been described in connection with preferred embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims.

(61) In this section, certain specific details of the disclosed embodiments are set forth for purposes of explanation rather than limitation, so as to provide a clear and thorough understanding of the present invention. However, it should be understood readily by those skilled in this art, that the present invention may be practised in other embodiments which do not conform exactly to the details set forth herein, without departing significantly from the spirit and scope of this disclosure. Further, in this context, and for the purposes of brevity and clarity, detailed descriptions of well-known apparatus, circuits and methodology have been omitted so as to avoid unnecessary detail and possible confusion.

(62) In the claims, the term comprising does not exclude the presence of other elements or steps. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Thus, references to a, an, first, second etc. do not preclude a plurality. Reference signs are included in the claims however the inclusion of the reference signs is only for clarity reasons and should not be construed as limiting the scope of the claims.