GB2358064A - Flow meter structure - Google Patents

Abstract

Structures and methods are disclosed for measuring fluid flow in an open channel, such as an irrigation channel. By making use of the measures disclosed, a non-intrusive meter, such as an electromagnetic flow meter may be reliably deployed where conventionally a mechanical meter would have been used. The invention also allows a non-intrusive meter, such as an electromagnetic flow meter to replace an existing mechanical flow meter in an open channel. A metering conduit is located towards the bottom of the novel flow meter structure, and a baffle directs liquid towards the metering conduit. This can reduce variation of the filling level in the conduit. The flow meter structure can be mounted to a sluice, for example slid into a groove for a sluice gate.

Description

2358064 FLOW METER STRUCTURE The present invention relates to a flow meter

for insertion into a channel and for determi g the flow of a liquid through the channel. The present invention relates in particular to flow measurement in a channel in which the liquid level may vary.

In most practical situations the channel will be an open channel (but could also be a closed channel) such as an irrigation channel, or one having at least one open portion along its length. In the following description such a channel will simply be referred to as an "open channeP.

Various flow meter arrangements for measuring the flow of a liquid through an open channel are known. One example of such an arrangement is illustrated in Figure 1. This figure shows a sluice 100 provided with a sluice gate 102 which can be moved up and down in a groove 104 so as to limit the flow of the liquid 106 (in this case water) through the open channel 108 to varying degrees. Situated downstream of the sluice 100 is a flow meter 110 commonly known as a "Deathridge wheel". This mechanical flow meter comprises an undershot wheel 112 with vanes 114 which are moved by water 106 flowing past the flow meter 110, thereby causing the wheel 112 to rotate. The speed of rotation is indicative of the flow rate. A major drawback associated with this type of flow meter is the fact that in particular at low flow rates the relationship between flow and rotation is non-linear. Further, this mechanical flow meter is vulnerable to vandalism and, having exposed moving parts, may also be a danger to children or animals.

Another type of flow meter employs ultrasonic techniques. The speed of the flow of the liquid and also the depth of the liquid are measured to determine the volume flow rate of the liquid. This type of flow meter requires relatively complicated apparatus, in particular because two physical properties have to be measured and processed.

The present invention has been made in view of the above problems associated with conventional flow meters.

2 Accordingly, in one aspect the present invention provides a structure for insertion into a channel and for measuring a flow of a liquid through the channel, the structure comprising a portion of vertically reduced cross section when compared with the overall vertical dimensions of the structure, such that, in use, the liquid flows through the portion of vertically reduced cross section, the structure further comprising a flow meter to measure the flow of the liquid through the portion of vertically reduced cross section. Because the liquid flows through the portion of vertically reduced cross section the problems associated with liquid filling only part of the channel are alleviated. Provided the liquid level is above a predetermined minimum liquid level (only in exceptional conditions such as extreme drought the liquid level might drop below this minimum level) the liquid would be expected always to fill the portion of vertically reduced cross section. Hence, more accurate measurements of the flow of liquid may be obtained without requiring measurement of the depth of the liquid.

Preferably, the flow meter is a non-intrusive flow meter such as an inductive flow meter. The flow area thus is not obstructed and is less susceptible to silting-up because the speed of the flow of the liquid is increased due to the smaller cross sectional area of the portion of vertically reduced cross section (assuming that its width is not increased).

In the most important application the liquid will be water, e.g. for irrigating farm land. The portion of vertically reduced cross section is preferably located towards the bottom of the structure when the structure is deployed.

Preferably, the portion of vertically reduced cross section is of generally rectangular cross section. This is preferred to, for example, a circular cross section, because the measurement and processing of the measured values is simpler with the rectangular cross section when compared with, for example, a circular cross section. In particular, inductive measurement using a rectangular shaped flow-section is independent of flow profile effects and thus partial blockage, for example, is irrelevant. Further, when an inductive flow meter is used, arranging the means for generating the magnetic field and the means for detecting the electric voltage transverse to the magnetic field and the direction of flow is relatively simple. In addition, since many open channels such as irrigation channels are of generally rectangular cross section the structure may be manufactured to suit the dimensions of the channel.

Preferably, the structure further comprises fixing means for securing the structure to a retaining formation of a sluice provided in or at the channel. This makes it particularly easy to install the structure in the channel. When the flow meter is intended to replace an existing flow meter situated near a sluice, the existing flow meter may simply be removed, and the structure accommodating the new flow meter may be fixed to the retaining formation of the sluice. The term sluice is used herein broadly to mean any form of moveable gate used to control flow in an open channel.

This concept is a further aspect of the invention. Accordingly, the present invention also provides a structure for insertion into a channel and for measuring a flow of a liquid through the channel, the structure comprising a housing body accommodating a flow meter; and fixing means for securing the structure to a retaining formation of a sluice provided in or at the channel.

Preferably, the fixing means is adapted to be secured to a groove of the sluice, such as found in many types of sluices. The groove is normally intended to receive a sluice gate for controlling the flow of liquid through the channel. If the structure is to be secured to a groove of the sluice, the existing sluice gate is simply taken out of the groove, and the fixing means is secured to the groove.

Preferably, the fixing means comprises at least one flange projecting laterally from the housing body.

Preferably, the flange is adapted to be slid into the groove.

Preferably, the structure further comprises filter means., such as a coarse screen for filtering the liquid. This may alleviate problems of obstruction of the portion of vertically reduced cross section.

Preferably, the structure further comprises a sluice gate. This is advantageous if the structure is mounted to a groove of an existing sluice because in this case the sluice gate of the existing sluice would have been removed.

4 Preferably, the sluice gate is moveable along one or more rail(s).

Preferably, the structure comprises moving means for moving the sluice gate in dependence upon the output of the flow meter. This enables the amount of liquid flowing through the channel to be regulated by closed loop control.

If the flow meter is of a type which requires a power supply to operate (such as magnetic or ultrasonic flow meters) the measuring apparatus preferably further comprises detection means for detecting whether or not any liquid is present in the channel within a predetermined range of the flow meter; and means for interrupting power supply to the flow meter in dependence upon an output of the detection means. This feature can result in reduced power consumption and cost savings. It is of particular advantage if the flow meter is battery powered since the life of the battery can be extended by up to several times.

In an aspect closely related to the first aspect the present invention provides apparatus for measuring liquid flow in a channel in which the liquid level may be subject to variation comprising baffle means for directing liquid flowing through the channel through a metering conduit of predetermined cross sectional area and of a lesser vertical extent than the maximum liquid height in the channel, the baffle being arranged so that, over a range of heights of liquid in the channel, substantially all of the liquid flowing through the channel is directed through the metering conduit and the metering conduit remains filled with liquid, and means for measuring liquid flow in said metering conduit.

In some cases, rather than directing substantially all of the liquid, only a predetermined portion may be arranged to flow through the metering conduit. By metering conduit is preferably meant a closed conduit such as a pipe (preferably of substantially rectangular section) and the means for measuring liquid flow preferably comprises a flowmeter, preferably an electromagnetic (or other non intrusive) flowmeter integrated with the conduit, the conduit preferably defining the metering bore of the flowineter. The length of the conduit need only be sufficient for the purposes of metering and, in the limiting case, may have negligible length in the dimension of the liquid flow. The liquid need not be a pure liquid, but may contain entrapped solids and may be, for example, a slurry or suspension.

Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:Figure 1 shows a schematic side view of a conventional flow meter arrangement; Figure 2 shows a perspective view of an embodiment of the present invention.

Figure 3 shows the measuring section formed by a portion of vertically reduced cross section in an embodiment of the present invention; and Figure 4 shows a partial view of the measuring section shown in Fig. 3.

The conventional flow meter illustrated in Figure 1 has been described above. The following description of a preferred embodiment of the present invention will be made with reference to an open channel through which water flows.

The structure 1 shown in Figure 2 has a generally cuboid shape with parallel side walls 2 for insertion into an open channel such that the side walls are oriented parallel to the longitudinal dimension of the channel. At the upstream end 3 thereof the side walls 2 are linked by a coarse screen 4 formed with parallel vertical bars 5. Alternatively, a coarse mesh extending between the side walls 2 could be used. The coarse screen 4 acts as a filter to prevent large items such as driftwood from flowing into or through the structure 1. Towards the other (downstream) longitudinal end 6 the side walls 2 are connected by a vertical end wall 7 which extends from the top of the structure - 1 - (at -the same height as the top of the side walls 2) to a height spaced from the bottom of the structure. Located at a level below the vertical end wall 7 and joining onto this vertical end wall 7 is an undershot measurement por-tion 8 incorporating an inductive flow meter described hereafter. The vertical extent of the portion 8 is smaller than the overall vertical dimensions of the structure 1 as defined by the vertical dimensions of the side walls 2. The measuring portion 8 shown in Fig. 2 is a conduit of generally rectangular cross section, having the same width as the spacing between the vertical 6 side walls 2. As shown in Fig. 2, the sides 9 of the measurement portion 8 are formed by extensions 9 of the side walls 2. The height and also the width of the measurement portion 8 should be selected to suit the range of flow rates for which the meter 1 will be used. In prototypes good results have been achieved using heights less than 20cm.

A pair of flanges 10 are provided on the side walls 2 at the upstream end 3. These flanges 10 can be separately attached to the side walls 2, e.g. by welding, or they can be formed by outward bending of a portion of the side walls 2.

A pair of vertically extending rails or runners 11 (only one being shown in Fig. 2; the other is located opposite the first) is mounted to the inside of the side walls 2 downstream of the screen 4.

Replacing an existing measurement arrangement as the one shown in Fig. 1 by one according to the present invention is as follows. The existing mechanical flow meter 110 is removed, and the existing sluice gate 102 is taken out of the grooves 104 of the sluice 100. The flanges 10 of the structure 1 shown in Fig. 2 are slid into the grooves 104 of the existing sluice 100. The structure is hence secured to the channel 108. A new sluice gate (not shown) is then slid into the rails 11.

Operation of the arrangement so far described is as follows. Water enters the structure 1 through the screen 4 at the end 3 and flows towards the end 6. The flow of water (indicated by arrow 12) can be limited by operating the new sluice gate. In the case shown in Fig. 2 this would be achieved by raising or lowering the sluice gate. It will be appreciated that other types of sluice gates such as pivotable sluice gates may be used in combination with appropriate mountings such as hinges. The water which has passed the sluice gate is constrained by the vertical end wall 7 to flow through the measurement portion 8, where measurement of the flow takes place. The water then leaves the structure 1 via the downstream end 6.

From the foregoing description it will be appreciated that the measurement portion 8 is always entirely filled with water provided the water level does not drop below the top edge

7 of the measurement portion 8.

The measurement portion 8 will now be described in more detail with reference to Figs. 3 and 4. A magnetic (or inductive) flow meter is shown as installed around the measurement portion 8. Reference numerals 13, 14 and 9 respectively denote top and bottom walls and the left side wall of the measurement portion 8 (only the left hand side is shown in Fig. 4; the right hand side has a corresponding configuration). An electromagnet with laminated magnetic circuit 16 and top and bottom coils 17 and 18 (as shown in Figs. 3 and 4 alternatively a permanent magnet could be used) is situated at the measurement portion 8 near the top and bottom walls 13 and 14 and extends over a substantial part thereof. The electromagnet powered together with a controller/processor 20 by a battery, generator, solar panel or mains connection, generates a magnetic field across the measurement portion 8, in the case shown in a vertical direction. Electrodes 19 are provided at the side walls 9 of the measurement portion 8, at least one at each side wall 9.

As shown in Fig. 3, water enters the measurement portion 8 at the right hand part of the figure, the bottom end of the vertical end wall 7 joining onto the measurement portion at the top right hand corner. A voltage horizontally across the measurement portion 8 is generated due to the flow of the water (arrow 12) through the magnetic field, as known per se. This voltage is detected via the electrodes 19 provided at the sides 9 of the measurement portion 8. The voltage is a function of the flow velocity and is communicated to a central controller 20 (shown in Fig. 2 only). The controller 20 includes means for processing the detected voltage, for example a storage device for recording the voltage (as indicative of flow rate) and the time of the measurement, and/or integrating it to record the total volume which has passed-through the meter, or a smoothed value indicative of average flow rate. The value of the detected volt e andlor derived data may be stored in the controller 20 or an external storage medium connected to the controller 20. In one embodiment the controller 20 includes or is connected to a transmitter for transmitting the data to a satellite. This is particularly advantageous because it enables the flow of water, i.e. water consumption, to be monitored at a remote location, and because the installation costs of this flow meter arrangement could be lower when compared with a connection by land line.

8 The electrodes 19 are fixed to the wall of the conduit 8 by suitable means such as a bolt 21 passing through the wall. Electrical connections also pass through the wall at this point. In the preferred embodiment the joint is therefore sealed by an 0-ring 22. Also in the preferred embodiment a tamper-proof cover 23 sealed by an 0-ring 24 gives access for servicing the electrode 19. Since the inductive flow meter forms a substantially sealed unit the risk of vandalism is reduced. Further, having no moving parts the structure 1 represents a smaller risk to children and animals than the mechanical flow meter 110 shown in Fig. 1.

The structure 1 may include an actuator (not shown) for operating the sluice gate. Any suitable actuator can be used, for example a chain driven by a reversible electric motor and connected to a rack and pinion on the sluice gate. This actuator can be controlled to operate in dependence upon an output of the flow meter by the controller 20. Thus the flow of water can be controlled to a required value.

The controller 20 is connected to a suitable detector (not shown) provided at or near the flow meter. The detector delivers an output to the controller 20 and, if this output indicates that no water is present or the depth (and thus the flow) is less than a minimum amount the controller 20 interrupts the power supply to the flow meter and switches to a stand-by mode. The detector monitors the presence of water either continuously or at intervals. When subsequently the output from the detector indicates that water is present power is again supplied to the flow meter.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed andlor illustrated features.

9

Claims (14)

CLAIMS:

1. A structure for insertion into a channel and for measuring a flow of a liquid through the channel, the structure comprising a portion of vertically reduced cross section when compared with the overall vertical dimensions of the structure, such that, in use, the liquid flows through the portion of vertically reduced cross section, the structure further comprising a flow meter to measure the flow of the liquid through the portion of vertically reduced cross section.

2. A structure according to Claim 1, wherein the flow meter is an inductive flow meter.

3. A structure according to Claim 1 or Claim 2, wherein, when the structure is installed, the portion of vertically reduced cross section is located towards the bottom of the structure.

4. A structure according to any preceding claim, wherein the portion of vertically reduced cross section is of generally rectangular cross section.

5. A structure according to any preceding claim, further comprising fixing means for securing the structure to a retaining formation of a sluice provided in or at the channel.

6. A structure for insertion into a channel and for measuring a flow of a liquid through the channel, the structure comprising:

a housing body accommodating a flow meter; and, fixing means for securing the structure to a retaining formation of a sluice provided in-or at the channel.

7, A structure according to Claim 5 or Claim 6, wherein the fixing means is adapted to be secured to a groove of the sluice.

8. A structure according to any of Claims 5 to 7, wherein the fixing means comprises at least one flange projecting laterally from the housing body and adapted to be received into the groove.

9. A structure according to any preceding claim, further comprising a debris screen as filter.

10. A structure according to any preceding claim, further comprising a sluice gate.

11. A structure according to Claim 10, further comprising moving means for moving the sluice gate in dependence upon an output of the flow meter.

12. A structure according to any preceding claim, wherein the flow meter is powered by a power supply, the structure further comprising detection means for detecting whether the flow of liquid in the channel is less than a predetermined amount, and means for interrupting power supply to the flow meter in dependence upon an output of the detection means.

13. Apparatus for measuring liquid flow in a channel in which the liquid level may be subject to variation comprising baffle means for directing liquid flowing through the channel through a metering conduit of predetermined cross sectional area and of a lesser vertical extent than the maximum liquid height in the channel, the baffle being arranged so that, over a range of heights of liquid in the channel, substantially all of the liquid flowing through the channel is directed through the metering conduit and the metering conduit remains filled with liquid, and means for measuring liquid flow in said metering conduit.

14. A structure substantially as herein described with reference to or as illustrated in Figures 2 to 4 of the accompanying drawings.