FR2776379A1 - Dust filter for gas meter having up- and downstream ultrasonic transducers - Google Patents

Abstract

Gas meter has two ultrasonic transducers (22,24) arranged at either end of a measurement conduit (20). Each of the transducers is held in an assembly (30,32) of cross section larger that the transducer cross-section. At least the downstream transducer (24) has a filter (46) placed within its mounting assembly (32), so that it extends over the whole transducer cross section. The filter is an effective dust trap, but still allows the passage of ultrasonic waves.

Description

The present invention relates to a gas meter comprising, an ultrasonic measurement conduit with a longitudinal axis comprising an internal part in which the gas flows and at least two ultrasonic transducers spaced along the longitudinal axis.

It is known that the gases whose flow rate is sought to transport various quantities of dust which are far from negligible.

Over time, dust eventually settles in different parts of the gas meter which are not always intended to receive it.

It therefore frequently happens that dust is deposited on the ultrasonic transducers, which has the effect of disturbing their operation and therefore of affecting the linearity of the ultrasonic measurements carried out.

To reduce the volume of dust conveyed by the flow of gas, it is known to provide in this type of meters, upstream of the ultrasonic measurement conduit, dust traps.

However, these dust traps are not always effective because they still allow lighter dust which can settle later on one and / or the other of the transducers.

It would therefore be interesting to find an effective solution to the dust problem.

The subject of the invention is therefore a gas meter comprising, an ultrasonic measurement conduit with a longitudinal axis comprising an internal part in which the gas flows at least two ultrasonic transducers spaced along the longitudinal axis, characterized in that said counter comprises between each transducer and said internal part of the measurement conduit an enlarged portion with respect to the dimensions of the active surface of said transducer said counter further comprising at least one element placed in at least one of said enlarged portions and extending over the entire internal width thereof so as to form a filter screen against the dust carried by the az said element being traversed by the ultrasonic waves emitted by the transducers over at least part of its width which is greater than dimensions of the active surface of said transducer.

By having in front of one and / or the other of the transducers an element forming a screen filtering the dust and which has a surface in contact with the flow of gas, offered to ultrasonic waves and whose width is greater than the dimensions of the active surface of the transducers the volume of dust is distributed over a larger surface than if said filter element had the same dimensions as the active surface of the transducers. Such a filter element is therefore unlikely to be obstructed over time.

According to one embodiment of the invention, said at least one element forming a filter screen is placed against the transducer.

According to another embodiment of the invention, said at least one element forming a filter screen is placed at a distance from the transducer.

Said at least one element forming a filter screen can be placed in front of the upstream transducer and / or in front of the downstream transducer depending on the configuration of the counter and, more particularly of the measurement conduit, of the enlarged portions and of the transducers.

Advantageously, the meter can comprise at least one obstacle positioned longitudinally in the internal part of the measurement conduit so as to form at least one annular passage for the flow of gas.

Preferably. the measurement conduit comprises an inlet and an outlet for the flow of gases which are respectively arranged between one of the enlarged portions and said measurement conduit.

The gas inlet and outlet each have, at the place where the gas flow, respectively, enters and leaves the measurement duct, a passage section offered to the gas whose normal is inclined relative to the axis longitudinal at an angle other than 90 "or may also be equal to 90
This orientation of the gas inlet and outlet makes it possible to better channel the gas flow than in the prior art and thereby the dust transported by this flow.

So. the dust is less directed towards the transducers than in the prior art.

When the meter provided with these oriented inlet and outlet also includes an obstacle such as that defined above, the flow is further channeled and the dust which is also channeled with the flow is kept away from the transducers, thereby reducing even the risks of contamination of said transducers.

The filter screen element is made of a material composed of metallic or synthetic fibers
The material can be of the type in which the fibers form a sieve or of the type in which the fibers are intertwined and distributed in a volume
The measurement conduit may for example take the form of an ellipsoid of revolution, of a tube or else have a rectangular cross section.

Other characteristics and advantages will appear during the description which follows, given solely by way of example and made with reference to the appended drawings in which - FIG. 1 is a schematic longitudinal view of an ultrasonic gas meter according to the invention. invention, - Figure 2 is an enlarged longitudinal view of the measurement conduit and the ultrasonic transducers shown in Figure 1 according to a first embodiment, - Figure 3 is an enlarged longitudinal view of the measurement conduit and the ultrasonic transducers shown in FIG. 1 according to a second embodiment, - FIG. 4 is an enlarged longitudinal view of the measurement conduit and of the ultrasonic transducers represented in FIG. 1 according to a third embodiment, - FIG. 5 is a partial enlarged view of the enlarged portion 50 shown in Figure 4, - Figure 6 shows an alternative embodiment of the enlarged portion 50 of Figure 4, - Figure 7 is a longitudinal view of an alternative embodiment of the measurement conduit shown in Figures 1 to 4, - Figure S is an enlarged view of the enlarged portion in which is placed screen element according an alternative embodiment of that shown in Figure 7, - Figure 9 is a longitudinal view of a second alternative embodiment of the measurement conduit shown in Figures 1 to 7, - Figure 10 is a longitudinal view of a third alternative embodiment of the measurement conduit shown in FIGS. 1 to 9, - FIG. 11 is a view of the cross section of the measurement conduit shown in FIG. 10.

FIG. 12 is a longitudinal view of a fourth alternative embodiment of the measurement conduit shown in FIGS. 1 to 9.

As shown in FIG. 1 and designated by the general reference noted 10, an ultrasonic gas meter comprises a housing 12 to which an inlet opening 14 for the gas flow is connected as well as an outlet opening 16.

An ultrasonic measurement block 18 is housed inside the bolt bowl 12 and comprises a measurement conduit 20 of longitudinal axis XX ′, for example produced in the form of a tube, at the ends of which two ultrasonic transducers 22,24 are positioned along said longitudinal axis.

The gas flow (indicated by arrows in the figures) enters through the opening 14 inside the housing 12, splits up on the wall of the ultrasonic measurement block 18 situated opposite said opening and is distributed in the interior volume compns between said housing and said ultrasonic measurement block.

The gas flow is directed towards the bassc part of the housing and rushes through an opening 26 made in the measuring block inside the latter.

The downward movement then the elbow effected by the flow going up towards the opening 26 allows said flow to get rid of a large part of the heavy dust which it conveys.

The flow then enters the internal part of the measurement conduit 20, in which the ultrasonic measurements of the gas flow will be carried out, by a supply 27 produced in the form of an annular opening, and escapes from said conduit by an outlet 28 also produced in the form of an annular opening.

The annular inlet and outlet openings have a gas flow section whose normal is inclined relative to the longitudinal axis at an angle which is substantially equal to zero in the example shown in Figures 1 and 2 .

The flow comes out of the measuring block 18 by going up through a chimney 29 which is arranged perpendicular to said measuring block and which communicates with the outlet opening 16 of the meter.

As shown in FIG. 1 and in more detail in FIGS. 2 to 4, the counter comprises, between each ultrasonic transducer 22, 24 and the internal part of the measurement conduit 20 in which the gas flows, a portion 30, 32 which forms a housing and a support for said corresponding transducer.

So. each of the annular inlet 27 and outlet 28 openings is arranged between one of said enlarged portions and the measurement conduit 20.

Each of the portions 30, 32 possible an enlarged transverse dimension with respect to the transverse dimensions of the active surface of the transducers.

Each portion has for example a generally cylindrical external shape which has an internal recess 34, 36 also of cylindrical shape and in which the corresponding transducer is mounted.

 Each of the portions has a peripheral flange 38, 40 extending the general cylindrical shape and which provides before each transducer a free space of cylindrical shape 42, 44 which has an enlarged transverse dimension relative to the transverse dimensions of the active surface of the transducers.

Taking into account the configuration of the measurement conduit and the direction of flow in the internal part of the measurement conduit which entrains the dust directly on the active surface of the transducer 24 it is preferable to place an element 46 at least in the free space 44 located in front of the downstream transducer 24 (fig. 2).

The element 46 is disposed against the transducer and extends transversely over the entire internal transverse dimension or width of said free space so as to form in front of said transducer a screen which acts as a filter preventing the dust transported by the gas d '' reach the transducer.

The filtering element is for example fixed by gluing on the annular part 32a of the portion 32 situated at the bottom of the free space and surrounding the transducer 24.

 The filtering material is also made of a material which is formed from metallic or synthetic fibers.

Each fiber constitutes an obstacle for the dust particles whose trajectory crosses this fiber.

In order to ensure correct filtration, a sufficient quantity of fibers should be provided.

The filter can be of the type while, that is to say that the dust particles are distributed over the almost flat surface of said filter.

The material is, for example, a stainless steel cloth, the diameter of the metallic fibers of which is 25 m and that of the interstices of 16 μm.

However. if it is desired to further increase the efficiency of the invention, it is preferable to provide a material making it possible to have a filter in which the dust particles are distributed in a volume.

Thus, with a material in which the fibers are entwined the filter is able to accumulate a greater quantity of dust than the filter of the sieve type before becoming clogged.

Such a material is for example cotton or fleece.

More specifically, the material is for example the product sold by the company 3M under the brand "FILTRETE 50g"
The density of fibers in the material is for example between 10 and 500 g / m2 and is for example of the order of 50 g / m2 and its thickness is equal to timm.

If the density of fibers in the material is less than 10 g / m2 then it is found that a very large thickness of filter is necessary to obtain sufficient filtering.

On the contrary, if the density of fibers in the material is greater than 500 g / m2 then it can be seen that the acoustic signal from the transducers is greatly attenuated which is unacceptable.

The size of the fibers is also an important parameter and it is preferable to have fine fibers for the same interstice between the fibers because the porosity of the filter will be higher.

The cone inside which the ultrasonic waves emitted by the transducer 24 are contained is indicated in dotted lines and designated by the reference noted 47 in FIG. 2.

The transverse dimension of the filter element surface 46 is greater than that of the active surface of the transducer and the filter element is, on the one hand, made of a material transparent to ultrasonic waves and, on the other hand, is placed in an area where the ultrasonic waves emitted by the transducer 24 pass through it over a part of its transverse dimension which is greater than the transverse dimension of the active surface of the transducer.

Consequently, when a given volume of dust particles is deposited on the filter element and partially obstructs it, the free part that the latter offers to the ultrasonic waves remains sufficient to allow their passage without too much attenuation.

However, when the filter element is placed against the transducer (fiL.3) and the material of the filter element is of the type in which the dust is distributed in a volume, it is possible to increase the thickness or dimension longitudinal of the material while reducing its density so that the ultrasonic waves are not too attenuated in the case where the quantities of dust are very high.

In fact, for the same quantity of dust, the volume of the material in which the ultrasonic waves propagate and in which the dust is deposited is enlarged and the fibers are also more widely spaced than before, which will cause a "dilution" effect. "dust and will allow the ultrasonic waves to propagate more freely in the material than with a reduced thickness.

The efficiency of filtration remains essentially the same.

It should be noted that if the thickness of the material is increased while maintaining the same density, the filtration efficiency will be increased, but the ultrasonic waves will be more attenuated.

In the case where the configuration of the measurement conduit and / or of the enlarged portion and / or of the filter element is such that in the absence of dust the filter element is traversed by the ultrasonic waves only on a part of its transverse dimension equal to the transverse dimension of the active surface of the transducer then, for the same volume of dust as that mentioned above, the filter element would be very strongly obstructed in its part traversed by the ultrasonic waves, this which would considerably affect their attenuation and therefore the flow measurement.

Advantageously, the filter element 46 placed in front of the transducer 24 makes it possible to eliminate the turbulences present in the flow which, if they occurred in front of said transducer, would affect the linearity of the measurements.

As shown in FIG. 3 in another embodiment, a filter element 48 similar to element 46 is placed in the free space 42 of the enlarged portion 30, 32 so as to also protect the transducer 22 against dust.

This precaution can be useful when the meter must be subjected to severe dusting tests or when it is planned to use it for the counting of gases deemed to be particularly loaded with dust.

According to a third particularly advantageous embodiment shown in FIG. A, each of the enlarged portions 50, 52 of generally cylindrical shape includes a peripheral flange 54, 56 extending said generally cylindrical shape and which provides a free space of cylindrical shape in front of each transducer 5S , 60.

The longitudinal dimensions of the flanges 54, 56 and the free spaces 58, 60 are respectively greater than those of the flanges 38, 40 and the free spaces 42, 44 of FIG. 2.

Thus the extension of the internal free spaces to the enlarged portions 50 52 makes it possible to position each filter element 62 64 at a distance from the corresponding transducer 22 24, thus leaving an area of the free space between the filter element and its corresponding transducer is at rest.

It would be possible to have in the free space 58 and / or 60 several filter elements of the screen type, offset along the longitudinal axis and the fibers and interstices of which are offset transversely between two consecutive filter elements in order to trap more large amount of dust than with a single filter of this type.

In such a configuration, it would be very advantageous to combine the two types of filter element by placing a "volume" filter (of the type in which the dust particles are distributed in a volume) distant from the transducer and a filter of the sieve type. between them to improve the reliability of the filtering. In fact, if a dust particle is not stopped by the filter
"volume" it would be definitively stopped by the sieve filter.

It could even be envisaged to fill the free space in front of the transducer with a single filter element of great thickness.

Figure 5 is an enlarged partial view of the portion 50 shown in Figure 4 which shows part of this portion, the other part being obtained by symmetry with respect to the longitudinal axis XX '.

In this figure, the filter element 62 is pinched between one end of the collar 54 which forms a shoulder 55 and a washer 57 which is secured to said end of the collar, for example by ultrasonic welding.

FIG. 6 represents an alternative embodiment of the enlarged portion 50 of FIG. 4 in which the flange 66 extends the cylindrical part of the enlarged portion 68 so as to give the free space 70 internal to said enlarged portion a bowl shape gradually flared in the opposite direction to the transducer.

The filter element 62 is positioned at a distance from the transducer in this flared shape space.

FIG. 7 illustrates an alternative embodiment of the measurement conduit shown in FIGS. 1 to 4 which here takes the form of an ellipsoid of revolution 72 as described in French patent 2,683,046.

The ellipsoid of FIG. 7 has a structural difference with that of French patent 2,688,046: the flow of fluid is produced by openings made in the wall of the conduit 72 and not around the transducers.

Two enlarged portions 74, 76 serving as housings for the ultrasonic transducers 7S, 80 each have an internal free space 82, 84 of gradually flared shape in which is placed a filter element 86, SS similar to those described with reference to FIGS. 4 and 6.

Two annular openings 90, 92 serving respectively as an inlet and an outlet for the flow of gas in the internal part of the measurement conduit 72 are arranged between each enlarged portion 74, 76 and said measurement conduit.

These openings each have at the place where the gas flow respectively, enters and leaves the measurement conduit 72, a passage section offered to the gas whose normal N is inclined relative to the longitudinal axis XX 'at an angle has different from 90.

For example, the tilt angle a is 45 ".

Furthermore, an elongated obstacle 94 having for example a general shape of a warhead is positioned on the longitudinal axis XX '.

This obstacle defines with the internal wall of the measurement conduit an annular passage 96.

Thanks to the annular shape of the passage 96 and the orientation of the normal N to the passage sections offered to the gas at the place where the gas flow, respectively, enters and leaves the measurement conduit 72, said gas flow is channeled which keeps the dust it carries on a path away from the transducers 78, 80.

With such a configuration, the filter element 86 placed in front of the upstream transducer 78 is not very dusty, while on the filter element 88 placed in front of the downstream transducer 80 there is a distribution of dust 98 at the periphery of said filter element as indicated in figure 7.

FIG. 8 shows another possible variant of an enlarged portion 100 usable with the measurement conduit 72 of FIG. 7 in which the free space 102 takes the form of a cylindrical space at the bottom of which the filter element 86 is placed against the transducer 78.

FIG. 9 illustrates another configuration of ultrasonic counter 110 in which only the measuring block 112 (housed inside an external housing) has been represented and which is described in patent application EP 0 682 773.

This measurement block includes a tubular measurement conduit 114 provided with inlet 116 and discharge 118 openings, normal to the passage section offered to the gas at the place where the gas flow, respectively, enters and comes out of the measurement conduit 114 forms with the longitudinal axis X, X 'an angle of 90 ".

An improvement compared to this configuration could consist in arranging the openings 116 and 118 according to an inclination forming with the longitudinal axis XX 'an angle less than 90 "in order to distance the flow and therefore the dust particles from the zone where are located the transducers.

An elongated obstacle 120 is positioned along the longitudinal axis inside the measurement conduit 114 to form an annular passage 122 in which the gas flows.

Two enlarged portions 124, 126 form an angle of 90 "with the longitudinal axis XX 'and thus allow the ultrasonic transducers 128, 130 housed in these portions to be offset.

The ultrasonic waves emitted by these transducers are reflected by the walls 132, 134 in the annular passage 122.

Two filter elements 136, 138 conforming to the description which has been made with reference to the preceding figures are mounted on the two ends of the obstacle 120.

 It would also have been possible to arrange these filter elements in the part of the enlarged portions 124, 126 where the transducers are located, in a position located 90 "from that shown in FIG. 9.

The gas meter 140 partially shown in longitudinal view in FIG. 10 comprises a measurement duct 142 of longitudinal axis XX ′, the cross section of which is shown in FIG. 11 is rectangular.

Two portions 144, 146 enlarged relative to the dimensions of the ultrasonic transducers 148, 150 are arranged on one 142a of the walls of the measurement conduit at an inclination relative to the longitudinal axis XX '.

The transducers 148, 150 are mounted at the bottom of the enlarged portions 144, 146 which serve as their housings and the filter elements 152, i 54 conforming to those described with reference to FIG. 4 are positioned at a distance from said transducers in the corresponding cylindrical free spaces 156, 15S.

The ultrasonic waves emitted by one of the transducers propagate along a V or W-shaped path.

The operation of such a counter where the path of the ultrasonic waves has a W shape is for example explained in the document EP 0591 855.

It should be noted that the two transducers could also be arranged on the opposite wall 142b of the measurement conduit or else one of the transducers can remain on the wall 142a and the other be mounted opposite on the opposite wall 142b of so that the two transducers are connected by a fictitious straight line YY 'perpendicular to their active surfaces and which cuts the longitudinal axis at an angle of inclination less than') () (Fi.19).

 It is also possible to use this configuration of conduit of rectangular cross section with the enlarged portions containing the ultrasonic transducers arranged at the opposite ends of said conduit.

Claims (12)

CLAIMS 1. Gas meter comprising, an ultrasonic measurement conduit (20; 72; 114; 142) of longitudinal axis (XX ') comprising an internal part in which the gas flows, at least two ultrasonic transducers (22, 24, 78, 80, 128, 130 148, 150) spaced along the longitudinal axis, characterized in that said counter comprises between each transducer and said internal part of the measurement conduit an enlarged portion (30, 32; 50, 52; 68; 74, 76) relative to the dimensions of the active surface of said transducer, said counter further comprising at least one element (46, 48; 62, 64; 86, 88; 136, 138; 152, 154) placed in at at least one of said enlarged portions and extending over the entire internal width of the latter so as to form a filtering screen with respect to the dust carried by the gas, said element being traversed by the ultrasonic waves emitted by the transducers over at least part of its width which is greater e to the dimensions of the active surface of said transducer. 2. Gas meter according to claim 1, wherein said at least one element (46, 48) forming a filter screen is placed against the transducer.  3. Gas meter according to claim 1, wherein said at least one element (62, 64; 86, 88; 136, 138; 152, 154) forming a filter screen is placed at a distance from the transducer. 4. Gas meter according to one of claims 1 to 3, wherein said at least one element (48; 69; 86; 136; 152) forming a filter screen is placed in front of the upstream transducer. 5. Gas meter according to one of claims 1 to 3, wherein said at least one element (46; 64; 88; 138, 154) forming a filter screen is placed in front of the downstream transducer. 6. Gas meter according to one of claims 1 to 5, comprising at least one obstacle (94; 120) positioned longitudinally in the internal part of the measurement conduit so as to form at least one annular passage for the gas flow. and to channel the dust flow away from the ultrasonic transducers. 7. Gas meter according to one of claims I to 6, wherein the measuring conduit comprises a supply (27; 90; 116) and an outlet (28; 92; 118) for the flow of gases which are respectively arranged between one of the enlarged portions and said measurement conduit. 8. A gas meter according to claim 7, in which the gas inlet and outlet each have at the place where the gas flow, respectively, enters and leaves the measurement conduit, a passage section offered to the gases whose normal is inclined with respect to the longitudinal axis at an angle other than 90. 9. A gas meter according to claim 7, in which the gas supply and discharge each have, at the place where the gas flow, respectively, enters and leaves the measurement conduit, a passage section offered to the gases whose normal is inclined with respect to the longitudinal axis at an angle equal to 90. 10. Gas meter according to one of claims 1 to 9, wherein said at least one element forming a filter screen is made of a material composed of metallic or synthetic fibers.  He. A meter according to claim 10, wherein the material is of the type in which the fibers form a screen. 12. Counter according to claim 10, in which the material is of the type in which the fibers are interlaced and are distributed in a volume. 13. Gas meter according to one of claims I to 12, wherein the measurement conduit is an ellipsoid of revolution (72). 14. Gas meter according to one of claims 1 to 12, wherein the measurement conduit is a tube (20; 114). 15. Gas meter according to one of claims I to 12, wherein the measurement conduit (142) has a rectangular cross section.