Apparatus and Method for Characterising Fluid Flow through a Pipe

DESCRIPTION

Background to the Invention

Measuring the flow-rate of a fluid through a pipe is often desirable. For example, it is desirable to monitor the flow of water through mains supply pipelines to ensure that sufficient water is supplied to the customer. Furthermore, as will be readily understood, when a pipeline is leaking the flow-rate through a pipe greatly increases. Therefore, leaks may be detected by monitoring the flow-rate of fluid through a pipe. Preferably the volumetric flow-rate of a pipe, i.e. the volume of fluid flowing through a pipe per unit of time, is monitored.

Generally, flow-rate meters are used to monitor the flow-rate through a pipe. In order to measure flow-rate with a flow-rate meter it is necessary that the meter is installed within the pipeline such that it is situated within the flow of fluid through the pipe. This is because flow-rate meters rely on the flow of the fluid physically acting upon movable components of the meter. For example, flow-rate meters often include one or more rotary blades that are pushed or otherwise propelled by the fluid and thereby drive a rotary potentiometer or other similar flow measuring device. However, as can be appreciated, installing a flow-rate meter within a pipe may be difficult.

Currently preferred methods of installing flow-rate meters and other flow characterising meters within a pipe involve interrupting the flow of fluid through the pipe. Most commonly, the fluid flow will be shut off causing interruption to the supply. Then a U-shaped additional section of the pipe will be joined in fluid communication with the pipe at each end. The U-shaped additional section of the pipe will include a pre-installed flow-rate meter and will be fixed to the pipe in a position such that the meter can be easily read and is serviceable. A valve is then fixed in the main pipeline between the two ends of the U-shaped additional section so that the main pipe may be sealed and such that any fluid flowing through the main pipe will be diverted through the U-shaped additional section and past the meter. Finally, the fluid flow through the pipeline will be restored and the fluid flow may be measured. If fluid is allowed to flow through the pipe during the process of fixing the U-shaped additional section to the main pipe fluid may leak out of the pipe.

Installing flow-rate meters within pressurised mains water pipes in order to measure the flow of water there-through in the manner set out above is particularly troublesome. Shutting off mains water pipes is undesirable as it will interrupt the supply of water to customers. Furthermore, space must be provided for the additional length of pipe to be installed.

Typically, the flow-rate meter installed within a U-shaped additional section of pipe, as described above, will be a helical full-bore meter that extends across substantially the whole cross-section of the additional U-shaped length of pipe. A helical full-bore meter comprises a turbine rotor with a plurality of helically shaped rotor blades rotatably mounted about an axis that is substantially parallel to the flow of fluid through the pipeline and radially central within the pipeline. Typically, the helical full-bore meters have metal turbine blades and are formed by casting. As the meter comprises a turbine rotor the turbine blades rotate in a direction normal to the fluid flow. The helical shape of the blades and the full-bore extent of a helical full bore flow-rate meter mean that such meters provide an accurate measure of flow-rate and are capable of measuring even very low flow-rates. However, helical full bore flow- rate meters are expensive to manufacture. Furthermore, in order to mount such meters within a pipe they must be formed within a separate length of pipe that is subsequently mounted within the existing pipeline, for example the additional U- shaped length of pipe described above. It is not possible to simply mount helical full bore meters within existing lengths of pipe without shutting off the fluid flow through the pipe and adding or replacing a length of pipe.

In order to characterise the fluid flow through a pipe without the need to temporarily shut-off the fluid flow or add additional lengths of pipe various methods of inserting characterising sensors, including flow-rate meters, through the side-wall of pipes have been proposed.

A preferred proposed apparatus for characterising fluid flow through a pipe comprises a saddle member for mounting upon the pipeline and a flow characterising meter. The saddle member has a first passage formed there-through that extends between a radially inner end of the saddle member and a radially outer end. A closure means for sealing the first passage is provided part-way along the passage. The closure means may, for example, be a ball valve or a shut-off plate. The flow characterising meter may be inserted into the outer end of the passage and extend through the length of the passage. A sealing means is disposed on the meter and/or the passage and may sealingly engage the meter with the passage when the meter extends part-way through the passage and the closure means seals the passage. The sealing means may also sealingly engage the meter with the passage when the meter extends through the length of the passage.

The apparatus described above is used in the following manner. First the saddle member is fitted to a pipe, which may be a mains water pipe, using an under pressure collar in a conventional manner. The saddle member is attached such that the radially inner end of the passage is adjacent the outer wall of the pipe. A hole is then provided in the wall of the pipe in correspondence with the passage of the saddle member. Typically, this is achieved by drilling a hole in the pipe through the passage of the saddle member. In order to avoid damage to the closure means it is necessary that the closure means is not sealing the passage when the hole is being drilled. After the hole has been provided the passage of the saddle member is sealed using the closure means in order to prevent fluid escaping from the pipe through the passage. In this manner a sealed access point to the hole in the pipe is provided by the closure means and the saddle member.

A flow characterising device having a flow-rate meter mounted substantially at an inner end is then partially inserted into the passage whilst the closure means keeps the passage sealed. The flow characterising device is inserted such that it is in sealing engagement with the passage. The closure means is then opened and the flow characterising device is fully inserted such that it extends through the passage and the A-

inner end of the flow characterising device extends into the fluid-flow within the pipe and the flow-rate meter is positioned within the pipe. Importantly, after the closure means is opened, the flow characterising device maintains its sealing engagement with the passage to prevent fluid leaking out the pipe through the passage of the saddle member.

The above-process is reversed to remove the flow characterising device from the pipeline. Due to the presence of the closure means, the pipe may be sealed even when no flow characterising meter is present within the passage.

The flow characterising device includes a flow-rate meter or other flow characterising sensor at an inner end. Importantly, any flow-rate meter or sensor must be small enough to pass through the passage of the saddle member. For this reason it is not possible to introduce full-bore flow-rate meters into a pipeline using this apparatus. An example of a flow-rate meter used in the above apparatus is a rotary paddle wheel that is designed to be mounted within the pipeline such that its rotational axis is normal to the flow of fluid within the pipeline. However, such flow-rate meters tend to be inaccurate and are incapable of accurately measuring the low flow-rates such as those found in domestic water mains during off-peak times.

Therefore, there is a need for a flow-rate meter that is accurate and can measure very low flow-rates and that may be inserted into a pipeline through a passage of a saddle member for example when mounted at an inner end of a flow-characterising device.

A further problem with the flow-rate meters that may be inserted into a pipeline through the passage of a saddle member is that it has been very difficult to accurately characterise the volumetric fluid flow through the pipeline from their readings. This is because the flow-rate meter is not a full bore meter and provides a measure of the velocity of the fluid flow only at the point at which it is inserted into the pipeline. There is no simple means or method for automatically converting this data into a volumetric flow-rate without further information. As will be appreciated by the person skilled in the art, in order to calculate the volumetric flow-rate through the pipe using conventional fluid dynamics it is necessary to know at least two further pieces of data. Specifically, the cross-sectional area of the fluid flow within the pipe and the position of the flow-rate meter within the fluid flow must be known or measured in order to calculate a volumetric K Factor that allows a volumetric flow-rate to be calculated from the velocity measured by a flow-rate meter

Currently, the problem of not knowing these further pieces of data is overcome by using estimated values. The as-manufactured inner diameter of any specific pipe is used as a measure of the inner diameter of the pipe. However, this value is often an over-estimate as sediment or build up on the inner walls of the pipe may reduce the inner diameter and introduce errors into the calculation of volumetric flow-rate. The value may also be an over-estimate as liners are often inserted in pipes (for example, in order to seal leaks) and the person monitoring the pipe may not be aware that a liner has been inserted. Furthermore, any particular flow-rate meter may be designed to be inserted within a pipeline a specified distance from the outer surface of the pipeline. The known as-manufactured thickness of the pipe on which the saddle member is installed may then be used to estimate the depth into the fluid flow that the flow-rate meter may be inserted. However, any sediment, build up or deformities within the pipeline will alter the actual depth from this estimated depth, introducing further errors into the volumetric flow-rate.

Therefore, there is a need for a method and system for minimising the errors in calculating the volumetric flow-rate of a pipeline from the velocity measurements of a flow-rate meter.

As explained above, current flow-rate meters are installed such that a reading from the meter can be easily read and is serviceable. That is, the read-out of flow-rate meters are designed to be manually inspected. This is true whether the flow-rate meter is a helical full-bore meter or a flow-rate meter installed in a pipeline through a saddle member. A typical flow characterising device may comprise a flow-rate meter and a data collection means. The data collection means may be a data-logger that logs data indicative of the variations in the flow-rate through the pipeline over time. This data can be collected if and when the flow-rate meter is manually accessed by a service person. However, in order to collect the data, the service person requires equipment capable of synchronising with any specific data logger. Furthermore, the data logger will only log the raw data provided by the flow-rate meter. That is, the velocity of fluid flow within the pipeline as measured by the flow-rate meter at each specific time. The service person will then have to use further pipeline specific data to calculate the actual volumetric flow through the pipeline, as explained above. For example, the cross-sectional area of the pipeline inner diameter and possibly the flow profile position of the flow-rate meter within the pipeline may need to be known.

In light of the above, there is a need for a method and apparatus for measuring the flow-rate of fluid through a pipeline that allows the flow-rate data to be easily calculated and collected without the need for specialist equipment or additional information. Preferably any such method and apparatus should also allow the data to be collected remotely without the need to manually access any flow-rate meter.

Summary of the Invention

The present invention provides a method for monitoring the volumetric flow-rate of a fluid passing through a pipe comprising the steps of:

• providing a saddle member fixed to a pipeline at a measurement site, the saddle member having a linear passage formed there-through extending between a radially outer end and a radially inner end; • providing a hole in the pipe in correspondence with the passage of the saddle member;

• measuring a depth from the radially outer end of the passage to a diametrically opposite inner wall of the pipe;

• measuring an outer diameter of the pipe; • inserting a flow-rate meter for measuring the velocity of the fluid flow through the pipe through the passage to a known depth from the radially outer end of the passage; and

• calculating from the measured depth, the outer diameter of the pipe and the known depth a volumetric K-factor specific to the measurement site for converting the velocity of fluid flow measured by the flow-rate meter to a volumetric flow-rate.

Using the method of the present invention the volumetric flow through substantially any pipe may be simply calculated to a reasonable degree of accuracy from the velocity readings produced by a flow-rate meter. The method of the present invention avoids the need to use inaccurate estimates of various dimensions to calculate a volumetric flow of fluid through a pipe and can be used for substantially any pipe, even when details of the pipe (such as its thickness) are not initially known. The method of the present invention also allows the calculated volumetric flow to take into account any irregularity in the size of the pipe, such as a build-up on the walls of the pipe or corrosion of the walls of the pipe.

The method of the present invention operates in the following manner. As will be understood by the person skilled in the art flow-rate meters provide an output that is indicative of the velocity of the fluid passing through the meter. In order to calculate a volumetric flow from this output conventional fluid dynamic calculations that require values of the cross-sectional area of the fluid flow and the positioning of the flow-rate meter within the fluid flow to be known are used. The method of the present invention provides measures of these values. First, a value for the inner diameter of the pipe is obtained from the measured depth of the radially outer end of the passage to the diametrically opposite inner wall of the pipe and the measured outer diameter of the pipe. The obtained value of the inner diameter can be used to estimate the cross- sectional area of the fluid flow by assuming the inner surface of the pipe is substantially cylindrical or has any other assumed cross-section. Second, as the outer diameter and inner diameter of the pipe are measured and the length of the passage of the saddle member is known it is possible to calculate the position of the flow-rate meter within the fluid flow. Using this information it is possible to calculate a volumetric K-factor for substantially any measurement site of any pipe.

The flow-rate meter used in the method of the present invention may be substantially any meter that can pass through the passage of the saddle member. Preferably the flow-rate meter will be a flow-rate meter as discussed below and as defined in any of claims 12 to 25.

In the method of the present invention the outer diameter of a pipe may be measured using any suitable method that will be apparent to the person skilled in the art. Alternatively, measurement of the outer diameter may be unnecessary because the pipe may be of a standard diameter or one that is known from records.

The saddle member may be a saddle member attached as described in the field of the invention section above and may be attached to the pipe using an under pressure collar in a manner that will be understood by the person skilled in the art. A hole may be provided in the pipe by drilling into the pipe through the passage of the saddle member.

As will be understood, placing a flow-rate meter within a fluid flow will provide a degree of blocking to the flow of fluid. The degree of blocking may be characterised by a blocking factor. In order to improve the accuracy of the K-factor produced by the method of the present invention it is preferable that a flow-rate meter that has a known blocking factor is used. This blocking factor can be incorporated into the calculations used to produce the K-factor in a manner that will be understood by a person skilled in the art and will thereby increase the accuracy of the calculated K- factor.

Preferably, the depth from the radially outer end of the passage to a diametrically opposite inner wall of the pipe is measured using a vernier gauge instrument. The vernier gauge instrument may be marked with a scale to indicate the depth to which it is inserted through the passage. Advantageously, the vernier gauge instrument will be such that it sealingly engages the passage of the saddle member and fluid cannot escape from the pipe out of the passage when the vernier gauge instrument is inserted through the passage. In a simple embodiment the vernier gauge instrument may substantially comprise a seamless metal tube that is marked with a scale point at an outer end.

However, other vernier gauge instruments may be preferred. For example, in order to obtain an accurate measure of the inner diameter of a pipe it may be necessary that the vernier gauge instrument comprises an elongate shaft that is much narrower than the passage of the saddle member. In such cases it is preferable that the elongate shaft is slidingly and sealingly mounted within a locking device that may be locked to and seal the outer end of the passage. This enables the elongate shaft to be inserted through the passage whilst the passage remains sealed by the locking device and the sealing engagement between the elongated shaft and the locking device.

Advantageously, the saddle member used in the method of the present invention further comprises a closure means that may be used to seal the passage part-way along its length and locking means substantially at the radially outer end of the passage. This allows the passage of the saddle member to be closed and prevent fluid from leaking out of the pipe when a flow-rate meter or a vernier gauge instrument is not inserted in the passage. The closure means may comprise a shut-off plate.

If the saddle member does comprise a closure means it is preferable that a flow-rate meter that is mounted upon a flow characterising device that may sealingly engage the outer end of the passage of the saddle member is used. It is also preferable that a vernier gauge instrument that may sealingly engage the outer end of the passage is used to measure the depth from the radially outer end of the passage to the diametrically opposite inner wall of the pipe. This is because using a flow characterising device and a vernier gauge instrument that may sealingly engage the passage allows the method of the present invention to be carried out without fluid leaking out of the pipe. Specifically, the closure means may seal the passage part- way along its length when neither the flow characterising device or vernier gauge instrument are inserted in the passage. The passage may then remain sealed until the either the flow characterising device or vernier gauge instrument are partially inserted within the passage and sealingly engage the outer end of the passage. The closure means may then be opened and the flow characterising device or vernier gauge instrument may be inserted through the passage whilst maintaining their sealing engagement with the outer end of the passage. This process may be reversed to remove either the flow characterising device or vernier gauge instrument from the passage.

The present invention also provides apparatus for monitoring the volumetric flow-rate of a fluid passing through a pipe comprising: a saddle member having a linear passage formed there-through extending between a radially outer end and a radially inner end and a closure means that may seal the passage part-way along its length; a vernier gauge instrument that may sealingly engage the passage; and a flow characterising device that may sealingly engage the passage and has a flow- rate meter mounted at an inner end.

This apparatus may be used to carry out the method of the present invention, as discussed above. The apparatus is particularly advantageous as it may provide an accurate measure of the volumetric flow through a pipe from a flow-rate meter that measures the velocity of fluid flow without the need to interrupt the fluid flow through the pipe. The apparatus is particularly suitable for use with domestic water mains pipes.

Preferably, the flow characterising device of the apparatus comprises a device locking means that may be used to removably lock the device to the radially outer end of the passage and an elongate shaft that is sealingly and slidably mounted within the device locking means and wherein the shaft has an inner end at which the flow-rate meter is mounted and an outer end that may be removably locked to the device locking means.

Preferably, the device locking means comprises an orientation specific locking means such as a bayonet fitting to ensure that the flow characterising device may be locked to the saddle member in only a single orientation. It is further preferable that either the elongate shaft cannot rotate within the device locking and/or the outer end of the flow characterising device may only be locked to the device locking means in a single specific orientation. In this manner it is possible to ensure that when the device locking means is locked to the saddle member and the outer end is locked to the device locking means that the flow-rate meter is oriented in a desired and known orientation within a pipe. For example, it may be possible to position a turbine rotor within a fluid flow such that its axis of rotation is substantially parallel to the flow of fluid through the pipe.

It may also be preferred that the device locking means may be semi-permanently locked to the saddle member. For example, one or more a screw members may be used to lock the device locking means to the saddle member. The, or each, screw member may be used to lock the device locking means to the saddle through a cooperative axially extending passage that is formed through the device locking means and extends into the saddle member. In order to prevent a flow characterising device being tampered with or removed from a saddle member by an unauthorized user it may be preferable that any screw member can only be tightened or loosened using a specific tool.

It may also be preferable that the flow characterising device comprises a pressure release valve. The pressure release valve may be formed such that, when open, it allows fluid communication between the interior of the saddle member and the external environment when the flow characterising device is in position within the saddle member. Such a pressure release valve may be beneficial as it can be used to release any pressure lock that is present and preventing complete removal of a flow characterising device from a saddle member. A pressure release valve may be formed through a device locking means of a characterising device or in any other suitable position as will be readily understood by the person skilled in the art.

It is also preferable that the device locking means of the flow-characterising device comprises a stop plate at a radially outer end. The stop plate will be formed such that when the device locking means is locked to a saddle member it is at a known distance from the radially outer end of the passage of the saddle member and therefore also at a known distance from the outer wall of a pipe upon which the saddle member is mounted. This stop plate thereby provides a reference surface. When inserting a flow- rate meter into a pipe the outer end of the elongate shaft will be slid through the device locking means until it is brought into face-to-face contact with the stop plate. This results in the flow-rate meter being inserted through the linear passage of the saddle member into the pipe a known reference distance.

It is also preferable that the vernier gauge instrument of the apparatus comprises a gauge locking means that may be used to removably lock the gauge to the radially outer end of the passage and an elongate shaft that has an inner end and is sealingly and slidably mounted within the gauge locking means.

It may also be preferable that the vernier gauge instrument comprises a pressure release valve. In the same manner as for the flow characterising device a pressure release valve may allow easy removal of a vernier gauge from a saddle member by releasing a pressure lock. A pressure release valve may be formed through a gauge locking means or in any other suitable position as will be readily understood by the person skilled in the art.

The preferred construction of the flow characterising device and the vernier gauge instrument of an elongate shaft and a locking means is preferable as it facilitates the insertion and removal of the device and/or the instrument through the passage without fluid leaking out of the passage. Specifically, the locking means of either the device or the instrument may be positioned adjacent an inner end of the elongate shaft. The locking means may then be attached to the outer end of the passage thereby sealing the outer end of the passage. The elongate shaft may then be slid through the passage and the locking means until the outer end of the elongate shaft is adjacent the locking means. The locking means and the outer end of the elongate shaft may then be locked together if a flow characterising device is being used. If the vernier gauge instrument is used the elongate shaft may be slid through the locking device until it hits the inner wall of the diametrically opposite side of the pipe and the depth of the pipe may be measured. In both cases the insertion of the elongate shaft is effected whilst the locking device is locked to the outer end of the passage and the passage is sealed by the locking device and the sealing engagement between the elongate shaft and the locking device.

In order that a vernier gauge instrument provides an accurate measure of the length from the radially outer end of the passage of a saddle member to the diametrically opposite inner wall of a pipe it may be preferred that an elongate shaft of the vernier gauge instrument is marked with a scale for measuring the position of the inner end of the shaft relative to the position of the gauge locking means. This scale may be a simple distance scale that indicates the length of the vernier gauge instrument that has been inserted into the passage. Alternatively, it may be preferable that the vernier gauge instrument further comprises an additional elongate scale member that extends radially outwards from an radially outer end of the gauge locking means and the elongate shaft of the vernier guage instrument has an outer end, wherein the position of the outer end of the elongate shaft relative to the elongate scale member provides a measure of the position of the inner end of the shaft relative to the position of the gauge locking means. The present invention also provides a flow-rate meter for removable insertion into a pipeline through a passage formed through the sidewall of the pipeline comprising a housing; an axle rotatably mounted within the housing; and a plurality of rotor blades mounted about the axle; wherein the blades are formed from a single blade piece that is formed from a planar sheet of material and comprises an radially inner annular mounting portion and a plurality of blade portions each connected to the annular mounting portion by a relatively narrow neck portion.

The flow-rate meter of the present invention is suitable for removable insertion into a pipeline through a passage formed through the sidewall of the pipeline. For example, the flow-rate meter may be mounted at the inner end of a flow-characterising device and inserted into a pipeline using a sealable saddle member, as discussed above. If a flow-rate meter according to the present invention is to be used in such a manner it is important that the flow-rate meter is small enough to fit through the passage of a saddle member. However, it may be preferable that the flow-rate meter is of the maximum size that allows it to pass through the passage in order to maximise area of the blades upon which the fluid may act.

The housing of the flow-rate meter provides support to the axle and the blades and allows them to rotate within the housing. Preferably the housing completely contains and protects the axle and the blades and allows substantially unimpeded fluid flow through the flow-rate meter in at least one direction. For example, if the flow-rate meter is a turbine rotor it is advantageous that the housing allows fluid to flow through the flow-rate meter in a direction substantially parallel to a longitudinal axis of the axle. However, it is to be appreciated that the only necessary function of the housing is that it supports the axle of the flow-rate meter, it is not necessary for the blades to be contained within the housing.

In a preferred embodiment of the present invention the housing of the flow-rate meter substantially comprises a cuboid box that is open at a first end and a second end that is opposite the first end and has a first cross-beam that extends across the first end and a second cross-beam that extends across and second end, wherein the axle is rotatably mounted substantially centrally within the housing by first and second cross-beams.

The flow-rate meter of the present invention may allow particularly low flow-rates to be measured. This is particularly true if the planar blade piece is thin and the volume per unit area of, and therefore the weight of, the blades is minimised thereby reducing the force required to drive the rotation of the flow-rate meter. Furthermore, forming the blades of the flow-rate meter from a single planar blade piece avoids casting deficiencies that might otherwise unbalance the rotor and thereby introduce inaccuracies in the measurement of the flow-rate.

Preferably, the blade piece, and therefore the blades, of the flow-rate meter are formed of stainless steel. In a preferred embodiment the blade piece is formed from plate of stainless steel that is less than 2mm thick. More preferably the stainless steel sheet is lmm thick. Advantageously, the thickness of the steel plate (or other material that forms the blade piece) is reduced to the minimum that is required to provide sufficient structural rigidity to the flow-rate meter within engineering tolerances. If the flow-rate meter is intended to be used in domestic a water supply it is important that a material suitable for use within drinking water, such as stainless steel, is used.

The blade piece may be formed from a sheet material using any suitable shaping method. However, it may be advantageous that the blade piece is formed using photo- etching. Photo-etching is preferred as it allows very thin sheet materials to be shaped accurately.

In order to form the flow-rate meter from the blade piece the annular mounting portion is mounted upon the axle and the blades are twisted into the correct orientation relative to the blade portion. The blades may be twisted into the correct orientation before or after the blade piece is mounted upon the axle. As the neck portions of the blade piece are relatively narrow compared to the blades, when twisting the blades into the correct orientation the blades and the mounting portion of the blade piece will remain substantially planar and undeformed and only the neck portions will undergo twisting deformation. The annular mounting portion of the blade piece is preferably mounted upon the axle such that it is normal to a longitudinal axis of the axle. As will be appreciated, the neck portions of the blade piece should be sufficiently narrow to allow the blades to be easily twisted into the correct orientation without undergoing significant deformation but must also be sufficiently broad to allow the blades to properly supported and maintained in position about the axle. Therefore, the relative circumferential angular width of the blades and the neck portions will be dependent upon the specific size and design of the flow-rate meter. Preferably the neck portions of the blade piece are no more than 50% of the angular width of the blades and more preferably will be less than 20% of the angular width of the blade pieces.

Preferably the blades are twisted such that they are each oriented at an acute angle to the longitudinal axis of the axle. In this manner the flow-rate meter of the present invention may operate as a turbine rotor that operates optimally when the flow of fluid through the meter is substantially parallel to a longitudinal axis of the axle.

It is particularly, advantageous that each blade is oriented at the same acute angle to the longitudinal axis of the axle in order to maximise the efficiency of the meter. Preferably the blades will be oriented at 45° to a longitudinal axis of the axle. However, it is important that the flow-rate meter is small enough to pass through the passage of the saddle member to be inserted into a pipeline; and increasing the angle of the blades increases the overall thickness of the rotor. Therefore the optimum angle of 45° may not be achievable and a different orientation may have to be used to reduce the size of the flow-rate meter.

Preferably, the blade piece and the flow-rate meter will be formed such that the blades are equally spaced around the axle. A preferred embodiment of a flow-rate meter comprises six blades although it is to be understood that flow-rate meters may have substantially any number of blades. For example flow-rate meters with twelve, eight or four blades would function appropriately.

When the flow-rate meter is positioned within a flowing fluid the rate of rotation of the flow-rate meter corresponds to the velocity of the fluid passing through the flow- rate meter. The rate of rotation of the blades may be detected using an induction pickup arrangement. In order for an induction pickup to be able to detect the rotation of the blades it is necessary that the blades of the flow-rate meter act as a magnetic pole.

In order to form a magnetic pole at each of the blades it is preferable that the blade piece is formed from a ferromagnetic material and the flow-rate meter further comprises a permanent magnet mounted upon the axle and in substantially uninterrupted magnetic communication with the blades through a ferromagnetic material. Advantageously, a flow-rate meter according to the present invention may include a permanent magnet that is substantially annular and mounted about the axle in a rotationally symmetric manner. It is further advantageous that an annular face of the permanent magnet may be held against the annular portion of the blade piece to allow magnetic communication between the permanent magnet and the blades. The field through the permanent magnet is preferably oriented such that it is substantially parallel to a longitudinal axis of the axle. In this manner each of the blades of the rotor may act magnetically as a pole of the permanent magnet and the space between adjacent blades will have a magnetic field of weaker magnitude. As the flow-rate meter rotates adjacent to a pickup arrangement, an alternating current may be thereby induced in the induction pickup arrangement as a flow-rate meter constructed in this manner rotates. The frequency of the induced current will be equal to the rotational frequency of the flow-rate meter multiplied by the number of blades of the meter.

In an exemplary embodiment of the present invention an annular permanent magnet is attached to the axle of the flow-rate meter in contact with the mounting portion of the blade piece such that a north pole of the magnet is in contact with the mounting portion. This will cause each blade of the flow-rate meter to be polarised as a north pole.

Mounting a permanent magnet annularly upon the axle of the flow-rate meter has been found to be particularly advantageous as it minimises the resistance to rotation that is caused when an induction pickup arrangement is used to detect the rotation of a flow-rate meter. Furthermore, this mounting provides the best rotational and dynamic balance to the flow-rate meter. Permanent magnets often contain materials that are not safe for long-term exposure to drinking water supplies. Therefore, it may be preferable that if the flow-rate meter of the present invention includes a permanent magnet and is intended for use within a domestic water supply the permanent magnet is totally enclosed by one or more enclosing bodies to prevent the magnet being brought into contact with a fluid flowing through the flow-rate meter. For example, it may be preferable that the permanent magnet is enclosed within a plastic enclosing body except for where it is in direct contact with the blade piece and thereby completely protected from contact with fluid flowing through the flow-rate meter.

Advantageously, the blade piece may be mounted upon the axle of the flow-rate meter by means of substantially annular clamping bodies also mounted upon the axle. For example, a first clamping body may be mounted upon the axle at a first side of the blade piece and a second clamping body may be mounted upon the axle at a second side of the blade piece. The first and second clamping piece may then be joined to one another through the gaps between the neck portions of the blade piece in such a manner that the blade piece is securely attached to the axle and the annular mounting portion of the blade piece is completely enclosed by the first and second clamping piece. If the flow-rate meter includes a permanent magnet in the manner described above the permanent magnet may also be enclosed within the clamping bodies and held against the blade piece by the clamping bodies.

If the flow-rate meter does comprise annular clamping bodies and the flow-rate meter is intended for use within a domestic water supply it is preferable that said bodies are made of non-toxic material, for example a polymer, that is suitable for exposure to a domestic water supply.

In order to allow the flow-rate meter of the present invention to accurately measure even very low flow-rates (i.e. flow-rates of 0.5 ms ^" or less) it is necessary to minimise the frictional forces that oppose rotation of the axle within the housing. Furthermore, in order to maximise the lifespan of the flow-rate meter of the present invention it is necessary to rotatably mount the axle within hard-wearing bearings. Therefore, in a preferred embodiment of the present invention the axle is mounted within the housing by means of a jewel bearing.

The flow-rate meter of said preferred embodiment is mounted within the housing such that the axle is allowed a small degree of sliding movement in a direction parallel to the longitudinal axis of the axle within the housing but the axle is prevented from sliding out of the housing. Advantageously, the axle of this embodiment has a pointed first end that is mounted within the housing substantially against a bearing plate. The first end of the axle is positioned such that axial thrust applied to the rotor by fluid flowing through the flow-rate meter drives the first end of the axle into the bearing plate. In this manner the bearing plate opposes the axial thrust applied to the axle and blades and, as the axle is pointed at the first end, the bearing plate minimises frictional forces that are generated by the axial thrust and that oppose rotation of the flow-rate meter. In order to minimise said frictional forces and to maximise the lifespan of the flow-rate meter the bearing plate is preferably made of a low-friction hard wearing material such as a synthetic jewel material, e.g. sapphire.

To further minimise frictional forces that oppose rotation of the axle within the housing it is preferable that the axle is mounted within the housing within annular bearings near the first end of the axle and near, or at, a second end of the axle. These bearings may also be made of a synthetic jewel material, such as sapphire.

As described above, the flow-rate meter of the present invention is preferably used with a flow characterising device that may be inserted into and extend through a passage formed through a saddle member and comprises a shaft having an inner end ^■ and an outer end. The flow rate meter may be mounted substantially at the inner end of such a flow characterising device and a locking means may be provided at substantially at the outer end of the shaft for removably locking the device in position within a saddle member.

Preferably the locking means is an orientation specific locking means, such as a bayonet fitting, and the flow-rate meter is mounted on the flow characterising device in a specific orientation relative to the locking means. By forming a flow characterising device in this manner it is possible to ensure that a flow-rate meter is always mounted in a specific orientation within a pipeline. For example, it is possible to ensure that the flow-rate meter is mounted within a pipeline such that the axle of the flow-rate meter is substantially parallel to the direction of fluid flow within the pipeline. It is even possible to ensure the flow-rate meter is oriented within a pipeline such that the fluid flows through the flow-rate meter in a direction from a second end of the axle to the first end of the axle.

As set out above, the rotation of the blades of the flow-rate meter of the present invention may be detected by a pick-up arrangement mounted adjacent an outer radial edge of the blades. Therefore, if the flow-rate meter is mounted substantially at an inner end of a flow characterising device it may be preferable that a pickup arrangement is formed within the flow characterising device adjacent its inner end and the flow-rate meter. The pickup arrangement may comprise at least one fixed search coil for inducing an electronic current in the presence of a varying magnetic field. Preferably, in order to amplify the current induced within the pickup by rotation of the blades adjacent the pickup, the pickup may further comprise an intensifer mounted within the shaft substantially at the inner end of the shaft of the device between the flow-rate meter and the search coil. Any such intensifier will act to enhance the magnetic flux produced when the blades of the flow-rate meter are rotated. The pickup arrangement may also comprise an amplifier for amplifying the output signal from the, or each, search coil. A head amplifier may be used, which will increase the output signal from the, or each, search coil and convert said output into a voltage square wave pulse.

Preferably the amplifier is a head amplifier that contains a micropower IC and a high- gain low-pass filter and the amplifier has a low offset voltage and a low gain bandwith product. Using a head amplifier within the flow characterising device of the present invention results in a high level of signal amplification with excellent immunity to noise and interference.

In an embodiment of the present invention where each blade of the flow-rate meter is polarised as a north pole of a permanent magnet as the blades of the flow-rate meter rotate adjacent to the pickup arrangement the magnetic flux will be intensified by any intensifier and may then generate an alternating current within the, or each, search coil. Finally, the output signal from the, or each, search coil will be amplified by an amplifier and converted into a voltage square wave pulse.

The magnetised blades of a flow-rate meter will have some attraction to any amplifier or intensifier and to the search coil of any pickup arrangement. This attraction will create a force opposing the rotation of the blades. Therefore, in order that very low flow rates can be accurately measured by the flow-rate meter, it is desirable to minimise this attraction. This can be done by utilising a very low level of magnetic flux. However, minimising the magnetic flux consequently reduces the voltage generated within the, or each, search coil. Therefore, as will be understood by the person skilled in the art, a balance between these two considerations is required. In a preferred embodiment of the present invention voltages of 0.3mV have been generated in a search coil by a rotating flow-rate meter.

A flow characterising device of the present invention may additionally comprise further sensors for monitoring the conditions within the pipeline. For example, a flow characterising device may further comprise a temperature sensor for measuring the temperature of any fluid within a pipeline and/or a pressure sensor for measuring the pressure of fluid within a pipeline. As will be understood, a flow characterising device may comprise any other suitable sensor. A sensor may be positioned in any suitable position on a flow characterising device. It may be preferable that a sensor is positioned within the fluid flow within a pipeline. In such situations that sensor may be positioned upon the housing of the flow-rate meter. Additionally or alternatively a sensor may be positioned on any suitable part of a flow characterising device that is substantially in contact with the fluid when the flow characterising device is positioned within the pipeline.

An intelligent cable may be used for providing an interface between a flow-rate meter and a data access point. A suitable intelligent cable comprises transmission means for transmitting a signal from the flow-rate meter to a data access point, an integral power supply and a programmable integrated circuit.

The intelligent cable operates in the following manner. A first end of the cable is provided with a signal produced by a flow-rate meter that is indicative of the velocity of fluid flowing through the flow-rate meter. The signal may be provided in any manner apparent to a person skilled in the art. For example, the signal may be provided from a pickup arrangement located adjacent the blades of a flow-rate meter. Preferably the intelligent cable is electronically connected to a pickup arrangement such that the pickup arrangement provides the intelligent cable with an amplified voltage that has a frequency that is indicative of the rate of rotation of the blades of the flow-rate meter.

The programmable integrated circuit (PIC) may be programmed with data specific to the flow-rate meter, the pipe in which the flow-rate meter is located and the location of the flow-rate meter within the pipeline. Using this information the flow-rate meter may convert the signal from the flow-rate meter into a signal indicative of the volumetric flow of fluid through the pipe. In particular, the PIC may be programmed with a volumetric K-factor that is calculated using the method of the present invention. The PIC may be additionally programmed with a linearisation program specific to the flow-rate meter.

The PIC may be programmed by connecting a programming device, such as a laptop to a connector of the intelligent cable. Alternatively, it may be necessary to directly access the PIC of the intelligent cable in order to program the PIC.

A suitable linearisation program for a specific type of flow-rate meter may be experimentally determined on a test-rig. In particular, a flow-rate meter may be calibrated to determine its linear flow factors for substantially any flow-rate using a test rig. These linear flow factors may then be converted to a known volumetric value based on a known relationship between the measured linear value and corresponding volumetric values determined using various standard pipe sizes on a traceable UKAS flow rig. In this manner, when the volumetric K-factor of a site installation is calculated a linear conversion factor can be determined for any signal produced by the flow-rate meter in order to convert the signal into a volumetric flow rate through the pipe. Therefore, by programming the PIC with the volumetric K-factor of the site installation and the linear flow factors of the flow-rate meter a volumetric reading may be accurately produced from a signal from a flow-rate meter by the PIC applying a suitable pulse density correction to the signal. A volume per pulse figure may be programmed within the PIC such that the signal output by the intelligent cable is in suitable units. For example, the PIC may be suitably programmed to provide an output pulse every time a predefined volume of fluid has passed through the pipe being monitored. For example, for a flow-rate meter installed within a domestic water mains pipe the intelligent cable may produce a pulse for every 100 litres of water that pass through the pipe.

Any suitable flow-rate meter may be used with an intelligent cable of the present invention. However, it is preferable to use a flow-rate meter according to any of claims 12 to 25, as discussed above.

Preferably the intelligent cable of the present invention further comprises a data logger for logging the signal from the flow-rate meter. This avoids the need to constantly monitor the flow-rate of a pipeline. The data-logger may be periodically accessed to obtain an analysis of the flow-rate of the fluid through a pipe over a period of time. The data-logger may continually log data from a flow-rate meter or may log the data over predefined time periods. Alternatively, the data logger may sample the flow-rate at predetermined intervals.

Advantageously, the intelligent cable of the present invention includes a conventional output adaptor. For example, the intelligent cable may a conventional 9-pin or USB output connector to allow the cable to be attached to a laptop or other computer. However, it is to be appreciated that substantially any output connector for connecting to a computer or other electronic analysis tool may be provided with an intelligent cable according to the present invention.

Alternatively or additionally, the intelligent cable may include wireless output means to enable an output signal of the data logger to be accesses remotely using a wireless enabled device. Any wireless output means may enable a data logger of the intelligent cable to be accessed wirelessly. This is particularly beneficial as it may allow the data from a flow-rate meter that is installed within an underground pipe to be accessed remotely without the need to manually inspect the pipe or flow-rate meter. Wireless access is advantageous when the flow through a domestic water pipe is being monitored. As will be understood, it may be preferable that the connectors of the intelligent cable and the intelligent cable itself are substantially waterproof. This is particularly important if the intelligent cable is to be used in sites where it may come into contact with water. For example, this may be particularly important if the intelligent cable is being used in connection with a flow-rate meter that is installed in a water mains pipe.

In these and other situations where waterproofing is necessary the connectors of the intelligent cable may comprise any conventional waterproof electronic connector.

Similarly, in order to waterproof the PIC it may be contained within a waterproof housing.

An apparatus for monitoring the volumetric flow rate of fluid flowing through a pipe: may comprise a flow characterising device according to any of claims 26 to 30 and an intelligent cable as discussed above. This apparatus is particularly advantageous as it allows the volumetric flow-rate of fluid flowing through a pipe to be simply and accurately monitored without the need for interruption to the supply of fluid through the pipe.

Further features and advantages of the apparatus and method of the present invention will be apparent from the preferred embodiments of the invention shown in the drawings and described below.

Drawings

Figure 1 is cross-sectional side view of a preferred embodiment of a flow-rate meter according to the present invention;

Figure 2 is a front view of the flow-rate meter of Figure 1 ;

Figure 3 is a cross-section of an apparatus for monitoring fluid flow through a pipeline comprising a saddle member and a flow characterising device, wherein the flow characterising device has a flow-rate meter according to Figures 1 and 2 mounted at an inner end;

Figure 3 a is a cross-section of an alternative embodiment of the apparatus of Figure 3 wherein the flow characterising device further comprises a pressure release valve;

Figures 4a to 4c are schematic diagrams showing the stages of inserting a flow characterising device of Figure 3 into the saddle member; Figure 5 is a side-view the flow characterising device of Figure 3 without the saddle member;

Figure 6 is a side-view of a preferred embodiment of a vernier gauge instrument that forms part of the apparatus of claims 26 to 30 and is suitable for use with the method of the present invention; and

Figure 7 is a side view of an intelligent cable that may form part of a preferred embodiment of the the present invention.

A preferred embodiment of a flow-rate meter 50 according to the present invention is shown in Figure 1. The flow-rate meter 50 is mounted at the sensor portion of a flow characterising device 2 as shown in Figure 4. The flow-rate meter is a turbine rotor and comprises an axle 57 that is rotatably mounted within a housing 51. Six turbine blades 52 are mounted and equally spaced about the axle 57.

The blades 52 of the turbine rotor 50 are formed from a single sheet of lmm thick stainless steel by photo-etching. After photo-etching the sheet of stainless steel a flat substantially blade piece is formed. This piece comprises a radially inner annular mounting portion to which six identical planar blades 52 are each attached by a narrow neck portion 64. The six blades 52 are substantially equally spaced around the blade piece. The central annular ring portion of the blade piece is held in position around the axle 57 by means of the clamping bodies 53 that are either side of the blade piece and completely enclose the mounting portion of the blade piece. Each blade 52 is twisted away from its initial coplanar orientation with the annular ring portion. After twisting the blades 52 are oriented such that the efficiency of the turbine rotor 50 is maximised for fluid flowing through the rotor in a direction parallel to the to the longitudinal axis of the axle 57 and the blades 52 do not protrude out of the housing 51. In particular, each blade 52 is oriented at the same angle to the longitudinal axis of the axle 57. In the illustrated embodiment of the invention each blade 52 is oriented at an angle of 50° to the longitudinal axis of the axle 57. As will be understood by the person skilled in the art the blades 52 are all twisted in the same direction relative to a radial direction of the axle 57 such that when fluid flows through the rotor in a direction parallel to the longitudinal axis of the axle 57 all of the blades 52 drive the rotor 50 to rotate in the same direction and a turbine rotor is formed. Furthermore, after twisting of the blades 52 from their initial coplanar orieήtation with the radially-inner annular portion each blade 52 remains substantially planar and undeformed. Instead, it is the material of the neck portions 64 that undergoes twisting deformation.

The axle 57 is slidably mounted within the housing 51 by means of a jewel bearing arrangement 54, 55, 56 which minimises the frictional forces opposing rotation of the axle 57. The axle 57 is mounted within the housing 51 at a second end within a second annular sapphire bearing 56 and is mounted near a first end within a first annular sapphire bearing 55. Furthermore, beyond the mounting of the axle 57 within the second annular sapphire bearing 55, a first end of the axle 57 is pointed. The pointed end of the axle 57 rests against a sapphire bearing plate 54. The first and second annular sapphire bearings 56, 55 are slidably mounted but contained within the housing 51. It is not possible for the axle 57 to slide out of the housing 51. As a result, when fluid flows through the turbine rotor 50 in a direction parallel to the longitudinal axis of the axle 57 and from the second of the axle to the first end the linear thrust applied to the axle 57 and blades 52 as a result of the fluid acting upon the rotational blades is substantially solely opposed by the sapphire bearing plate 54 acting upon the first end of the axle 57. As the bearing plate 54 is hard and the first end of the axle 57 is pointed the frictional force that is generated by the linear thrust and that opposes rotation of the axle 57 is minimised.

As set out above, the blades 52 are held in position around the axle by means of the annular clamping bodies 53. The annular clamping bodies are made of a non-toxic polymer material. The clamping bodies 53 also enclose an annular permanent magnet 58 that is held against the annular ring portion of the blade piece in such a manner that one of its annular faces of the permanent magnet 58 is held in contact with a face of the blade piece. The magnet 58 is aligned such that the magnetic field within the magnet 58 extends in an axial direction parallel to the axle 57.

As the magnetic permeability of the stainless steel blades 52 is greater than the magnetic permeability of a fluid flowing between the blades 52, the permanent magnet 58 results in each blade 52 becoming an effective magnetic pole with the gaps between each blade 52 acting as an opposing pole. Thus, when the flow-rate meter rotates any fixed point adjacent flow-rate meter and adjacent the radially outer edge of the rotating blades 52 will experience a magnetic flux that alternates polarity at a rate six times the rotational frequency of the axle 57.

A pickup arrangement is mounted adjacent the radially outer edge of the blades 52, as shown in Figures 1 and 2. The pick up arrangement substantially comprises an intensifier 62, a search coil 61 and an amplifier 60. The intensifier 62 is located closest to the blades 52 and operates to intensify the alternating magnetic field produced by the blades 52 as they rotate past the intensifier. This intensified magnetic field then induces an alternating electrical current within the search coil 61. The frequency of the induced alternating current is six times the frequency of rotation of the flow-rate meter 50 as the flow-rate meter has six blades 52. The induced alternating current is amplified by the amplifier 60, which also transforms it into a pulsed square wave voltage. This signal may then be transmitted to a processing unit or data logger and used to analyse the flow-rate of the fluid within a pipe.

A cross-section of an apparatus for monitoring fluid flow through a pipeline is shown in Figure 3. The apparatus substantially consists of a saddle member 1 and a flow characterising device 2. The saddle member 1 is attached to a pipeline 7 in a conventional manner by means of an under pressure collar (not shown). The saddle member 1 includes a shut-off gate 8 that may be used to seal a central passage 9 formed within the saddle member when the flow characterising device 2 is removed from the portion of the passage adjacent the gate. A hole is provided in the pipeline 7 through which the flow characterising device 2 protrudes into the fluid 10 within the pipeline.

As shown in Figure 5, the flow characterising device comprises an elongated shaft 30 having a sensor portion at an inner end and an end portion 32 at an outer end. The elongated shaft 30 is substantially cylindrical and the sensor portion is substantially cuboid. The sensor portion comprises a flow-rate meter 50 according to the present invention, as shown in Figures 1 and 2. The flow-rate meter has a back face 40 and the flow-rate meter 50 and the back face 40 extend radially beyond the central portion of the elongated shaft 30. The central portion of the elongated shaft 30 is sealingly and slidably mounted within a passage 20 formed through a casing 27. The elongated shaft 30 is maintained in sealing engagement with the passage 20 by two annular sealing rings 41 mounted substantially at either end of the passage. The sliding of the elongated shaft 30 through the casing 27 is limited by the sensor portion and the end portion 32. The flow-rate meter 50 comprises a housing 51 within which a six blade 52 turbine rotor is mounted.

The flow characterising device 2 may be releasably and sealingly engaged with the saddle member 1 by means of cooperating bayonet fitting portions 34 formed at an outer end of the saddle member and on the casing 27. Two annular rubber seals 35 formed around a first end of the casing 27 ensure the sealing engagement of the casing with the saddle member 1. The end portion 32 of the flow characterising device 2 may be releasably engaged with an outer end of the casing 27, as shown in Figure 3. The end portion 32 and the casing 27 are coupled by means of cooperating bayonet fitting portions 36 formed thereon. The bayonet fitting portions 36 ensures that the flow characterising device 2 can only be fixed within the saddle member 1 in a specific orientation relative to the flow of fluid 10 through the pipeline 7. In this manner it is ensured that the flow-rate meter 50 is always correctly aligned within the pipe 7.

The casing 27 of the flow characterising device 2 further comprises a stop plate 82 that acts as a depth stop. When the end portion 32 and the casing 27 of the flow characterising device are coupled the end portion 32 is in face-to-face contact with the stop plate 82, as shown in Figure 5. In this position the flow-rate meter 50 is a known reference distance from a radially outer face of the stop plate 82. Thus when the flow characterising device 2 is inserted through and coupled with a saddle member 1, as shown in Figure 3, and the end portion 32 of the flow characterising device 2 is in face-to-face contact with the stop plate 82 the distance of the flow-rate meter 50 from the stop-plate is known. Therefore, as the distance from the radially outer face of the stop plate 82 to the outer surface of the pipe 7 may also be known, or may be calculated it is simple to calculate the distance the flow-rate meter 50 has been inserted into the pipe 7.

A pickup arrangement is provided within the shaft 30 of the flow characterising device 2 adjacent the flow-rate meter 50. The pickup arrangement comprises an intensifier 62 a search coil 61 and an amplifier 60, as shown in Figures 1 and 2. The pickup arrangement acts to convert the rotation of the blades 52 of the flow-rate meter 50 into an electronic signal having a frequency proportional to the rate of rotation of the blades 52 of the flow-rate meter 50.

The flow characterising device 2 has a three-pin male connector 80 formed at its outer end. The male connector 80 is mounted on and extends from a connector plate 81. The three-pin male connector 80 is connected to the pickup arrangement by a cable (not shown) that passes through the length of the elongated shaft 30 such that the signal generated by the pickup arrangement is communicated to the male connector 80. The male connector 80 can then be connected to a suitable external electronic device (not shown) to obtain the signal produced by the flow-rate meter 50. For example, the male connector 80 may be connected to the intelligent cable 90 shown in Figure 7 and described below.

Figure 3a shows an alternative embodiment of a flow characterising device 2'. The flow characterising device 2' is substantially the same as the flow characterising device 2 of Figure 3 and Figure 5 except that it further comprises a pressure release valve 12. The pressure release valve 12 allows fluid communication between an outer side of the casing 27 of the flow characterising device 2' and the central passage 9 of a saddle member 1 when the flow characterising device is positioned within the saddle member by means of a fluid passage 13 formed therebetween. When the pressure release valve 12 is opened fluid is allowed to flow through the fluid passage 13.

The apparatus of Figure 3 is used in the following manner. First the saddle member 1 is attached to the pipeline 7 using the under pressure collar. The pipeline may, for example, be a 6 inch (0.152m) water mains pipe. The hole is then drilled in the pipeline 7 in correspondence with the passage 9 through the saddle member 1 using a drill (not shown) extending through the passage 9. During the drilling the shut-off gage 8 is withdrawn from the passage 9 to allow a drill bit to pass through uninhibited. The drill is then withdrawn from the passage 9 and the passage is sealed using the shut-off gate 8. In this manner a sealable access hole is provided in the pipeline 7. Figures 4a, 4b and 4c show the stages of inserting the flow characterising device 2 into a saddle member 1. The initial position is shown in Figure 4a. The passage 9 of the saddle member 1 is sealed by the shut-off gate 8 and the elongated shaft 30 is slidably positioned within the casing 27 such that the casing is as close to the flow- rate meter as possible.

The casing 27 of the flow characterising device 2 is then coupled to the saddle member 1 by means of the cooperating bayonet fitting portions 34 formed on the casing 27 and the saddle member 1, as shown in Figure 4b. The annular rubber seals 35 ensure the flow characterising device 2 is sealingly engaged with the saddle member 1. In this position the flow-rate meter 50 is within the passage 9 of the saddle member 1 but is also substantially adjacent to the casing 27 such that the passage 9 may remain sealed from a pipeline by the shut-off gate 8.

The shut-off gate 8 is then removed and the elongated shaft is slid through the casing 27 until the end portion 32 is in contact with the casing, as shown in Figure 4c. The end portion 32 is then releasably coupled with the casing 27 using the cooperating bayonet fitting portions 36. In this position the flow-rate meter may extend out of the saddle member 1 and into fluid flowing through a pipeline. The bayonet fitting portions 36 and the cooperating bayonet fitting portions 34 ensure that the flow-rate meter 50 is always correctly aligned within the pipe.

The force required to slide the flow-rate meter into a pressurised pipeline is minimised in this apparatus. This is a result of the shape of the flow-rate meter and the elongated shaft 30 of the flow characterising device. Both are small enough to pass through the passage 9 of the saddle member 1. As a result, when the flow-rate meter 50 and the elongated shaft 30 are contained within the passage 9 there is a gap between the walls of the passage and the flow-rate meter 50 and between the walls of the passage and the elongated shaft 30. However, the elongated shaft 30 has a substantially smaller cross-sectional area than the flow-rate meter 50 such that, when the flow characterising device 2 is positioned within the saddle member 1, an intermediate volume 38 may be formed between the saddle member, elongated shaft and flow-rate meter 2. When the shut-off gate 8 is removed fluid may flow (e.g. from the pipeline 7) between the flow-rate meter 50 and the saddle member 1 into the intermediate volume 38 formed between the elongated shaft 30 and the saddle member. This is particularly beneficial if the fluid within the pipeline pressurised, as pressurised fluid within the intermediate volume 38 will provide a force upon the back face 40 of the flow-rate meter 50 acting to push it into the pipeline. In this manner the action of pressurised fluid within the intermediate volume 38 may at least partially counteract the effect of pressurised fluid within the pipeline 7, which will act upon a front face of the flow- rate meter 50 to push it out of the pipeline. The force required to slide the flow-rate meter 50 into a pipeline 7 is thereby reduced. In order to increase this effect the back face 40 of the flow rate meter may be substantially circular and have an area that is just less than the minimum cross-sectional area of the passage 9. Forming the back face 9 in this manner will maximise the area upon which the pressurised fluid within the intermediate volume 38 will provide a force.

A flow characterising device 2 may be removed from a saddle member 1 by reversing the above process. In particular, first the end portion 32 is uncoupled from the casing 27 and the pulled back to the position shown in Figure 4b. The shut-off gate 8 is then reinserted to seal the central passage 9 from the fluid within the pipeline 7. Finally, the casing 27 is uncoupled from the saddle member 1 and the flow characterising device is removed.

If the flow characterising device 2' comprises a pressure release valve 12 and fluid passage 13 these features can be used to facilitate the removal of the flow characterising device 2' from a pipeline 10. In particular, when a flow characterising device 2' is being removed from a pipeline in the manner set out above and the shut- off gate 8 has been reinserted a pressure lock may be formed in the intermediate volume 38. This pressure lock can make the removal of the flow characterising device 2 from the saddle member 1 difficult, even after the casing 27 has been uncoupled from the saddle member 1. Opening the pressure release valve 12 at this point releases any pressure lock and makes the removal of the flow characterising device 2' much easier.

Figure 6 is a side view of a preferred embodiment of a vernier gauge instrument 70 that forms part of the apparatus of claims 26 to 30 and is suitable for use with the method of the present invention. The vernier gauge instrument 70 comprises a gauge locking means 73, an elongate shaft 71 and an additional elongate scale member 72 extending from a radially outer end of the gauge locking means 73. The gauge locking means 73 has a cylindrical central passage 75 formed there-through extending from an inner end to an outer end. The elongate shaft 71 is formed from a seamless metal tube and has a diameter substantially the same as the central passage 76. In this manner the elongate shaft 71 is shaped to sealingly engage and be passed through the passage 75 of the locking means 73. A rubber o-ring 78 is mounted within the passage 75 adjacent the outer end of the locking means 73 to sealingly engage the elongate shaft 71 with the passage 75. The elongate shaft 71 has a pointed inner end 77.

The elongate shaft 71 has a zero mark substantially at its outer end. The elongate scale member 72 has a corresponding distance scale marked on its lower edge. The position of the zero mark of the elongate shaft 71 on the distance scale of the elongate scale member 72 indicates the depth the inner end 77 has been inserted through the passage 75 of the locking means 73 past a known initial reference depth. At the initial reference depth an outer end of the elongate shaft 71 rests against a radially extending reference portion of the scale member 72.

The vernier gauge 70 may be used to measure the depth of a space that may only be accessed through a small hole. For example, the vernier gauge 70 can be used to measure the inner diameter of a pipe. When used with the method of the present invention the locking means 72 of the vernier gauge is locked to an outer end of a passage 9 of a saddle member 1 , for example a saddle member as shown in Figure 1. The locking means 73 comprises a cooperative bayonet fitting that allows it to be locked to a saddle member 1. Two rubber o-rings 74 are provided at the inner end of the locking means 73 to ensure that the locking means 73 is locked to a saddle member 1 in a watertight manner. The known initial reference depth of the vernier gauge 70 is at a known distance from the outer end of a passage 9 formed through a cooperating saddle member 1 when the locking means 73 is locked to the saddle member.

After the locking means 73 is locked to a saddle member 1 mounted upon a pipe. The elongate shaft 72 is passed through the passage 75 until the inner end 77 of the shaft 72 becomes incident upon a diametrically opposed inner surface of the pipe. The position of the zero mark of the elongate shaft 71 relative to the distance scale of the elongate scale member 72 may then be used to measure the distance of the inner surface of the pipe from the outer edge of the locking means 73. The thickness and inner diameter of the pipe may then be found using simple arithmetic as the outer diameter of the pipe may be measured and the length of the locking means 73 and saddle member 1 are known.

An intelligent cable 90 that may form part of a preferred embodiment of the present invention is shown in Figure 7. The intelligent cable 90 substantially comprises a central inline housing 91 that is connected a first end to a three-pin female connector

93 by a length of cable 92 and that is connected at a second end to a 9-pin connector

94 by another length of cable 92. The central inline housing 91 of the intelligent cable 90 is waterproof.

The three-pin female connector 93 allows the intelligent cable 90 to be connected to the flow characterising device 2 of Figures 3 and 5. Specifically, the female three-pin connector 93 of the intelligent cable 90 may be attached to the three-pin male connector 80 of the flow characterising device 2 such that signal produced by the pickup arrangement as a result of the rotation of the blades 52 of the flow-rate meter 50 is transmitted to the intelligent cable 90. A connection formed between the female connector 93 of the intelligent cable 90 and the male connector 80 of the flow characterising device 2 is substantially waterproof.

A signal input into the intelligent cable 90 from a flow-rate meter 50 will be transmitted to the inline housing 91. The inline housing 91 contains a programmable integrated circuit (PIC) (not shown). The PIC of the inline housing 91 is programmed to convert an input signal from a specific flow-rate meter 50 at a specific site location into an output signal that is indicative of the volumetric flow-rate of fluid through the pipe in which the flow-rate meter 50 is mounted. In particular, the PIC is programmed to convert the input signal into a volumetric signal on the basis of a volumetric K- factor for the site location and the linear flow factors of the specific flow-rate meter 50. The volumetric K-factor of the site location may be calculated using the method of the present invention. The volumetric signal produced by the PIC may provide a pulse for each unit of volume that passes through the pipe at the site location. For example, the signal produced by the PIC may provided a pulse for every 100 litres of fluid that flow through the pipe.

After the input signal has been converted by the PIC it is transmitted through a length of cable 92 to the 9-pin connector 94. The 9-pin connector 94 may then be connected to a computer (not shown) to access the volumetric signal and/or a data logger (not shown) for logging the signal produced by the PIC. The data logger may be capable of being wirelessly accessed such that it is not necessary to physically access the intelligent cable 90 to monitor the signal produced by the PIC. The PIC may be suitably programmed when a computer is attached to the intelligent cable 90. In particular, a computer may be used to programme the PIC with the volumetric K- factor for the specific site location and with the linear flow factors of the flow-rate meter 50.

Currently, the PIC of the preferred embodiment of the intelligent cable 90 is programmed by opening the inline housing 91 and directly accessing the PIC. However, it is to be appreciated that in other embodiments of the intelligent cable, a PIC may be programmed by connecting a suitable programming device (not shown), for example a computer, to either the 9-pin connector 94 or the three-pin female connector 93.