Patent Description:
The present invention also relates to a method of using a clamp-on ultrasonic transducer for measuring flow rate of a fluid through the pipe.

Ultrasonic, clamp-on, transit-time flow metering is extensively used for measuring flow of liquids and, to a lesser extent, gases in pipes. This type of metering involves clamping two or more transducers (or "sensors") to the outside of a pipe in which a liquid is flowing. One transducer generates an ultrasonic wave that enters the pipe wall, and travels through the liquid. The wave can then couple through the pipe wall and be detected by the second transducer or bounce within the liquid column several times before being detected by the second transducer, which can be clamped on the same side or on the opposite side of the pipe as the first sensor. The process is reversed so that the second transducer generates an ultrasonic wave that travels along the same path (but in the opposite direction) and is detected by the first transducer. The difference in the transit time for these two wave packets is related to the liquid flow rate through the pipe. The wave that travels generally in a downstream direction (i.e., with the flow) takes a shorter time to cover the same distance, than the other wave which generally travels in an upstream direction.

Reference is made to <CIT> and <CIT> which describe clamp-on type ultrasonic flowmeters.

A significant component cost is the cost of the transducers. Typically, the transducers are made from polyetheretherketone (PEEK) and may be enclosed in a stainless-steel housing for protection. Although PEEK has superior mechanical properties for ultrasonic wedges in that it has favourable elasticity and low attenuation, it is expensive in both material and manufacturing costs compared to most other plastics since the starting material is expensive and requires extensive machining starting from a solid bar or block.

Although injection moulding of PEEK is possible, if components are made using PEEK, then they tend to be made using PEEK containing a filler, such as glass fibre. Introducing other materials into PEEK, especially if they introduce inhomogeneities, tends to increase ultrasonic attenuation. Moreover, injection moulding of PEEK tends to require specialist machines, operating at higher pressures and temperatures than is normally required for injection moulding materials, such as ABS. The moulds for injection moulding PEEK also need specific design considerations.

According to a first aspect of the present invention there is provided a clamp-on ultrasonic transducer. The clamp-on ultrasonic transducer comprises an ultrasound-propagating wedge having a first face and a second face which is inclined to the first face. The clamp-on ultrasonic transducer further comprises a first piezoelectric element which is mounted on the second face and which is directed obliquely at the first face. The wedge has a width, w, between first and second side walls, wherein the width, w, is less than or equal to <NUM>. The first face is flat and is a bottom face of the wedge. The second face and a third face, adjacent to the second face, form a top face of the wedge. The third face is parallel to the first face and the second face is inclined relative to the first face. This can help to reduce the cost of manufacture, for example, by allowing the wedge to be made by injection moulding when it might otherwise not be possible to form from injection moulding and/or allow the transducer to be used with pipes of a range of diameters.

The wedge may be injection moulded. The wedge may consist of or essentially consist of polyetheretherketone (PEEK). If the wedge consists of or essentially consists of PEEK, then the wedge is preferably injection moulded and, more preferably, does not contain any filler, such as glass fibre.

The width, w, is preferably between <NUM> and <NUM>.

The clamp-on ultrasonic transducer may comprise a third face which is parallel to the first face, and a second piezoelectric element mounted on the third face and which is directed perpendicularly at the first face. Thus, the second piezoelectric element can be used to send waves perpendicularly through the pipe wall to obtain a value for ultrasound velocity in a fluid in the pipe.

According to a second aspect of the present invention there is provided a clamp-on ultrasonic transducer assembly comprising a pipe clamp comprising first and second parts closeable around a pipe, at least one hinge on a first side of the pipe clamp, at least one closure (for example, a clasp) on a second side (preferably opposite side) of the pipe clamp and at least one slot in the first or second part for receiving at least one sensor such that when the first and second parts are closed around the pipe, the sensor is presented to the pipe, and at least one sensor comprising the clamp-on ultrasonic transducer received in the at least one slot.

According to a third aspect of the present invention is provided a method of using the ultrasonic transducer installed on a pipe through which a fluid flows, the method comprising using a first piezoelectric element for a flow measurement and using the second piezoelectric for obtaining a value for ultrasound velocity in a fluid in the pipe.

According to a fourth aspect of the present invention is provided a computer program comprising instructions to cause the clamp-on ultrasonic transducer installed on a pipe through which a fluid flows, to perform the steps of the method of the third aspect of the present invention.

Referring to <FIG>, a clamp-on ultrasonic transducer assembly <NUM> is shown clamped around a pipe <NUM>. The pipe <NUM> extends along a longitudinal axis <NUM> and comprises a pipe wall <NUM> having an outer surface <NUM>. The clamp-on ultrasonic transducer assembly <NUM> (herein also referred to as a "clamp-on assembly", "clamp-on flow meter" or simply "flow meter") comprises a generally cylindrical, two-piece plastic pipe clamp <NUM> having first and second parts <NUM>, <NUM> (or "halves").

Referring also to <FIG>, the first and second pipe clamp parts <NUM>, <NUM> comprise generally half-cylinder-shaped shells <NUM>, <NUM> held together by a pair of hinges <NUM><NUM>, <NUM><NUM> (mostly obscured in <FIG>) spaced apart along one side of the pipe clamp <NUM> and by a pair of closures <NUM><NUM>, <NUM><NUM> (herein referred to as "clips" or "clasps") spaced apart along the opposite side of the pipe clamp <NUM>.

The pipe clamp <NUM> holds first and second sensors <NUM>, <NUM><NUM>, <NUM><NUM> in fixed positions in first and second slots <NUM><NUM>, <NUM><NUM> respectively which are spaced apart along the pipe <NUM>. The slots <NUM><NUM>, <NUM><NUM> have dimensions which match those of the sensors <NUM><NUM>, <NUM><NUM> such that the sensors <NUM><NUM>, <NUM><NUM> fit securely in the slots <NUM><NUM>, <NUM><NUM>. Thus, the slots <NUM><NUM>, <NUM><NUM> can be used to locate the sensors <NUM><NUM>, <NUM><NUM> precisely with respect to each other. The pipe clamp <NUM> presses the sensors <NUM><NUM>, <NUM><NUM> against the outer surface <NUM> of the pipe wall <NUM>. A single slot (not shown) or slots <NUM><NUM>, <NUM><NUM> which are longer than the sensors <NUM><NUM>, <NUM><NUM> which can allow the separation of the sensors <NUM><NUM>, <NUM><NUM> to be varied.

The same sensors <NUM>, <NUM><NUM>, <NUM><NUM> can be used with other, pipe clamps (not shown) having generally the same configuration as the pipe clamp <NUM>, but arranged to fit pipes of other, different sizes (i.e. pipes having greater or smaller outer diameter). Thus, identical sensors <NUM> can be produced, while different sizes of the pipe clamps (not shown) can be formed, thereby allowing clamp-on flow meters (not shown) for different sizes of pipes to manufactured easily and/or cheaply.

Referring in particular to <FIG>, the first pipe clamp part <NUM> comprises an elongate, generally half-cylinder-shaped shell <NUM> (or "body") in which the first and second slots <NUM><NUM>, <NUM><NUM> are provided as rectangular through-holes. The first pipe clamp part <NUM> includes first and second first hinge parts <NUM><NUM>, <NUM><NUM> (each first hinge part <NUM><NUM>, <NUM><NUM> forming one half of a hinge <NUM><NUM>, <NUM><NUM>) integrally formed with the shell <NUM>. Each first hinge part <NUM><NUM>, <NUM><NUM> comprises an outwardly- and downwardly-extending arm <NUM><NUM>, <NUM><NUM> supporting a stub or pin <NUM><NUM>, <NUM><NUM>. The first pipe clamp part <NUM> also includes first and second first closure parts <NUM><NUM>, <NUM><NUM> (each first closure part <NUM><NUM>, <NUM><NUM> forming one half of a respective closure <NUM><NUM>, <NUM><NUM>) integrally formed with the body <NUM>. The first closure parts <NUM><NUM>, <NUM><NUM> comprise a flap <NUM><NUM>, <NUM><NUM> having an aperture <NUM><NUM>, <NUM><NUM> having an inner wall <NUM><NUM>, <NUM><NUM> providing a retaining surface.

Referring in particular to <FIG>, the second pipe clamp part <NUM> comprises an elongate, generally half-cylinder-shaped shell <NUM> (or "body"). The second pipe clamp part <NUM> includes first and second second hinge parts <NUM><NUM>, <NUM><NUM> (each second hinge part <NUM><NUM>, <NUM><NUM> forming one half of a hinge <NUM><NUM>, <NUM><NUM>) integrally formed with the shell <NUM>. Each second hinge part <NUM><NUM>, <NUM><NUM> comprises an outwardly-extending arm <NUM><NUM>, <NUM><NUM> supporting a respective half collar <NUM><NUM>, <NUM><NUM> for receiving a respective pin <NUM><NUM>, <NUM><NUM> form the first pipe clamp part <NUM>. The second pipe clamp part <NUM> includes first and second second closure parts <NUM><NUM>, <NUM><NUM> (each second closure part <NUM><NUM>, <NUM><NUM> forming one half of a clasp <NUM><NUM>, <NUM><NUM>) integrally formed with the body <NUM>. The second closure parts <NUM><NUM>, <NUM><NUM> takes the form of a barbed head comprising an inclined leading edge <NUM><NUM>, <NUM><NUM> (or "ramp-like tooth") and a perpendictilar trailing edge <NUM><NUM>, <NUM><NUM> for engaging with the retaining wall <NUM><NUM>, <NUM><NUM>.

Referring to <FIG>, the sensors <NUM> take the form of ultrasonic transducers comprises an ultrasound-propagating element <NUM> (or "wedge") made from polyetheretherketone (PEEK). The wedge <NUM> is sufficiently narrow that it allows the wedge <NUM> to be formed by injection moulding, in particular at lower pressures and temperatures than normal. The wedge <NUM> does not include a filler, such as glass fibre, to reinforce and/or to facilitate manufacture. The wedge <NUM> is also sufficiently narrow that is can be used on a variety of pipe diameter, for example, from <NUM> to <NUM> or more.

The wedge <NUM> generally takes the form of a rectangular prism having a chamfer. The wedge <NUM> comprises a first face <NUM> (herein referred to as a "bottom face"), and second and third faces <NUM>, <NUM> (herein referred to as a "first top face" and "second top face" respectively) opposite the first face <NUM>. The bottom face <NUM> is flat and is in direct contact with the outer surface <NUM> of the pipe wall <NUM>.

The first top face <NUM> is inclined to the bottom face <NUM>. The second top face <NUM> lies parallel to the bottom face <NUM>. The normal <NUM> of the bottom face <NUM> and the normal <NUM> of the first top face <NUM> subtend an angle <NUM>.

The wedge <NUM> also includes fourth and fifth opposite faces <NUM>, <NUM> (herein referred to as "first side" and "second side" respectively). The bottom face <NUM> of the wedge <NUM> has a width, w, which is equal to or less than <NUM>, preferably between <NUM> and <NUM> and more preferably <NUM>. The bottom face <NUM> is preferably the narrowest part of the wedge <NUM>. The wedge <NUM> also includes sixth and seventh opposite faces <NUM>, <NUM> (herein referred to as "first end" and "second end" respectively). The bottom face <NUM> of the wedge <NUM> has a length, l, between the first and second ends <NUM>, <NUM>. The length, l, is greater than the width, w, and is less than <NUM>. The wedge <NUM> has a height, h, between the bottom face <NUM> and the second top face <NUM>, which is between about <NUM> and <NUM>.

The sensor <NUM> includes a first piezoelectric element <NUM> which is mounted on the first top face <NUM> and which is directed obliquely at the bottom face <NUM>. The sensor <NUM> also includes a second piezoelectric element <NUM> which is mounted on the second top face <NUM> and is directed perpendicularly to the bottom face <NUM>.

Referring also to <FIG>, when the sensor <NUM> is in contact with a pipe wall <NUM>, the area of contact is a narrow rectangular region having width less than the width, w. This is because the bottom face <NUM> is flat and the pipe wall <NUM> is curved. The wedge <NUM> is narrower compared to conventional wedges. By making the wedge <NUM> narrower, not only are material costs reduced, but also the volume of the wedge <NUM> is reduced to a size where it can be more easily injection moulded.

The bottom face <NUM> of the wedge <NUM> may be moulded so that it is cylindrically concave (i.e., transversely concave and longitudinally straight) thereby helping to increase the area of contact. Alternatively, the bottom face <NUM> of the wedge <NUM> may be machined after moulding so that it is cylindrically concave. Even if such a wedge <NUM> is machined after moulding, there can still be a significant cost saving in the quantity of material used and the amount of machining required, and potentially increase manufacturing rate.

As hereinbefore described, the sensor <NUM> can be used on any diameter of pipe <NUM> and can take the form of an insert in a pipe clamp <NUM> (<FIG>). The pipe clamp <NUM> (<FIG>) can be configured for use with any size of pipe <NUM>. Thus, a faulty or damaged sensor <NUM> can be easily replaced by slotting a replacement sensor <NUM> into an appropriate slot <NUM><NUM>, <NUM><NUM> (<FIG>).

Referring in particular to <FIG>, the piezoelectric elements <NUM>, <NUM> adapted for a given frequency of operation can be can easily be replaced with ones operating at a different frequency. The sensor <NUM> may also be used in a sealed unit (not shown). The ultrasonic sensor <NUM> has two piezoelectric elements <NUM>, <NUM>. However, only one in a pair of sensors <NUM> may use both piezoelectric elements <NUM>, <NUM>, although each sensor <NUM> in the pair may include two piezoelectric elements <NUM>, <NUM> (with one element <NUM>, <NUM> in one sensor <NUM> being redundant) for efficient manufacturing.

Referring to <FIG> and <FIG>, a bracket <NUM> used for holding electrical connectors <NUM>, <NUM> (not shown in <FIG>) and loading screws <NUM>, <NUM> can also be adapted to hold the piezoelectric elements <NUM>, <NUM> in position. The piezoelectric elements <NUM>, <NUM> can have a wrap-around electrode (not shown) or be provided with electrodes (not shown) on both sides, if a shallow channel (not shown) is machined into the wedge <NUM> to accept a soldered wire <NUM>, <NUM> (not shown in <FIG>).

In the illustrated embodiment, the piezoelectric elements <NUM>, <NUM> are shown held in by a clamping arrangement using loading plates <NUM>, <NUM>. However, the piezoelectric elements <NUM>, <NUM> can be glued into position using a layer of adhesive (not shown) between a piezoelectric element <NUM>, <NUM> and the wedge <NUM>. The piezoelectric elements <NUM>, <NUM> can be coupled to the wedge <NUM> via a thin layer of grease (not shown) or elastomeric material (no shown). Preferably, a jig (not shown) is used to glue the elements <NUM>, <NUM> to help ensure accurate and reproducible placement.

Referring in particular to <FIG>, when excited, the first piezoelectric element <NUM> emits an ultrasonic wave <NUM> along a path <NUM>. When excited, the second piezoelectric element <NUM> can send an ultrasonic wave <NUM> along a path <NUM> into the pipe <NUM> and through the liquid <NUM> so that, knowing the pipe material and dimensions, the ultrasonic velocity in the liquid <NUM> can be measured and used in the calculation of the flow velocity, or used to calculate the temperature of the liquid <NUM>.

Other measurements methods can be used. For example, if the internal diameter of the pipe <NUM> is known, then a signal processor (for example, in the form of a microcontroller or a computer) can determine the speed of sound in the liquid <NUM> without further information (e.g. without information about material properties). Alternatively, if the outside diameter of the pipe <NUM> is known and information about the pipe material are known, then the signal processor can determine the speed of sound in the liquid <NUM>.

Referring also to <FIG>, a measurement system (not shown) can perform a measurement of flow rate of the fluid <NUM> through the pipe <NUM>.

The measurement system (not shown) uses a first piezoelectric element <NUM> of, for example, the first sensor <NUM><NUM> (together with a first piezoelectric element <NUM> of the second sensor <NUM><NUM>) to perform a flow measurement (step S1). The measurement system (not shown) uses the second piezoelectric element <NUM> of the first or second sensor <NUM><NUM>, <NUM><NUM> to obtain a value for ultrasound velocity in a fluid in the pipe (step S2). The measurement system (not shown) uses the measured value of ultrasonic wave velocity to calculate the flow rate (step S3).

First and second transverse through-holes <NUM>, <NUM> pass between the first and second sides <NUM>, <NUM>, proximate to the first and second ends <NUM>, <NUM>. The through-holes <NUM>, <NUM> can be used to receive a rod or bar (not shown) for locating the wedge <NUM> in the clamp <NUM> (<FIG>) and for providing a point from which a spring (not shown) can urge the wedge <NUM> against the pipe <NUM>.

Claim 1:
A clamp-on ultrasonic transducer comprising:
an ultrasound-propagating wedge (<NUM>) having:
a first face (<NUM>) ; and
a second face (<NUM>) which is inclined to the first face; and
a first piezoelectric element (<NUM>) which is mounted on the second face and which is directed obliquely at the first face;
wherein the wedge has a width, w, between first and second side walls (<NUM>, <NUM>), the width, w, is less than or equal to <NUM>
characterised in that
the first face is flat
the first face is a bottom face of the wedge,
the second face and a third face, adjacent to the second face, form a top face of the wedge, and
the third face is parallel to the first face and the second face is inclined relative to the first face.