CA1259820A - Flow meter for measuring the flow rate of liquid - Google Patents
Flow meter for measuring the flow rate of liquidInfo
- Publication number
- CA1259820A CA1259820A CA000490285A CA490285A CA1259820A CA 1259820 A CA1259820 A CA 1259820A CA 000490285 A CA000490285 A CA 000490285A CA 490285 A CA490285 A CA 490285A CA 1259820 A CA1259820 A CA 1259820A
- Authority
- CA
- Canada
- Prior art keywords
- weir
- flow rate
- liquid level
- liquid
- flow
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Measuring Volume Flow (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A flow meter for measuring the flow rate of a liquid, capable of detecting the liquid level in the upstream space with respect to a weir and determining the flow rate of the liquid on the basis of the relation between the liquid level and the flow rate of the liquid that flows through the weir, wherein the width of the weir is designed so that the ratio of the variation of flow rate caused by a fixed variation of liquid level to the total flow rate at the existing liquid level is constant regardless of the liquid level.
A flow meter for measuring the flow rate of a liquid, capable of detecting the liquid level in the upstream space with respect to a weir and determining the flow rate of the liquid on the basis of the relation between the liquid level and the flow rate of the liquid that flows through the weir, wherein the width of the weir is designed so that the ratio of the variation of flow rate caused by a fixed variation of liquid level to the total flow rate at the existing liquid level is constant regardless of the liquid level.
Description
1~98~() The present invention relates to a flow meter for measuring the flow rate of a liquid. The flow rate of a liquid can be determined by measuring the level of the liquid on the upstream side of a weir, provided that the relation between the liquid level on the upstream side of the weir and the flow rate of the liquid through the weir at the existing li-uid level is known. The present invention relates particularly to the construction of a flow meter equipped with such a weir. Although condensation evaporates again when the pressure changes, condensation flows through the weir without evaporating, because the same pressure prevails in the space before the weir and in the space after the weir. Therefore, the flow meter of the present invention is useful particularly for measuring the condensation in a steam piping.
The applicant of the present application has been engaged in the development of a flow meter employing a so-called proportional weir in which the flow rate of the liquid is proportional to the liquid level on the upstream side of the weir. The interior space of the casing of this flow meter is pàrtitioned by a vertical wall into an-up-stream space having an inlet formed in the upper part of the same and connecting to the measured system, and a downstream space having a liquid discharge port formed in the lower part of the same, the upstream space and the downstream space communicate with each other by means of a space above the partition wall, a float valve capable of automatically dis-charge the liquid is provided at the liquid discharging port, and the liquid level in the upstream space is measured with a float or the like. Since the flow rate of a liquid ;; --1--.
that flows through an orifice is proportional to the square root of the distance from the liquid surface to the orifice, the proportional weir is a vertically elongate slit decreas-ing upward in width.
The flow rate measuring accuracy of the above-mentioned proportional weir reduces with the decrease of the flow rate, because the measuring error in measuring the liquid level in the upstream space is caused by the turbulence of the liquid surface and/or the resistance between the contact surfaces of the sliding members of a mechanism for con-verting the displacement of the float into the correspond-ing electric signal and those factors causative of the measuring error are constant regardless of the liquid level, and hence the de'gree of the influence of those factors causative of the measuring error on the measuring accuracy i6 enhanced as the flow rate decreases.
It is a technical subject of the present invention to provide a so-called constant-accuracy weir in which the ratio of the variation of the flow rate to the variation of the liquid level is reduced as the flow rate decreases and thereby the flow rate can be measured with constant measuring accuracy regardless of the liquid level, by turn-ing into account a fact that the liquid level measuring .; -2-1~59~3;~() error is practically constant regardless of the liquid level.
The technical means of the present invention taken to solve the above-mentioned technical problems comprises a weir of a shape designed so that the ratio of the variation of the flow rate caused by a fixed variation of the liquid level to the total flow rate at the existing liquid level is constant regardless of the liquid level.
The width of the weir is decided through the following numerical calculations. First, values for the flow rate measuring accuracy and the flow rate at a liquid level cor-responding to the bottom of the weir are specified. Secondly, an orifice which provides the specified flow rate at the liquid level corresponding to the bottom of the weir and a flow rate meas`uring accuracy not greater than the speci-fied value is designed. Thirdly, assuming that the weir consists of a plurality of rectangular orifices each of a fixed minute height piled up one over the other, the res-pective widths of the rectangular orifices are decided so that the ratio of an increment of flow rate given by placing a rectangular orifice to the total flow rate coincides with the specified flow rate measuring accuracy.
1~598c:0 The functions of the above-mentioned technical means are as follows. The liquid flows through the inlet into the upstream space defined by the partition wall, them flows through the orifice and the weir into the downstream space, and then flows outside through the outlet. Since the re-lation between the liquid level in the upstream space and the flow rate at the weir is known, the flow rate at the weir is obtained on the basis of the measured liquid level.
The ratio of the increment or decrement of the flow rate for a fixed variation of the liquid level to the total flow rate is constant and coincides with the specified measuring accuracy, as far as the range of the variation of the liquid level in the upstream space is within the height of the weir. On the other hand, liquid level measuring error is practically constant as in the conventional liquid levei mea~urement, regardless of the liquid level. Accordingly, the flow rate measuring accuracy is constant regardless of the liquid level.
The characteristic effects of the present invention are as follows. Since the flow rate measuring accuracy of the flow meter of the present invention is constant re-gardless of the liquid level, the flow meter of the present invention is capable of accurately measuring the flow rate ~259820 regardless of the flow rate or the variation of the flow rate.
In a constant-accuracy weir employed in the present invention, the flow rate varies as an expo-nential function of the liquid level, therefore, the constant-accuracy weir has a flow rate measuring range far wider than that of a conventional propor-tional weir of the same height.
In the drawings:
Figure 1 is a sectional view of the detect-ing unit of a flow meter, in a preferred embodiment, according to the present invention; and Figure 2 is an end view of an exemplary weir according to the present invention, and a graph showing the relation between the height of the liquid level at the weir and the flow rate.
A preferred embodiment of the above-mentioned technical means will be described hereinafter in con-nection with Figs. 1 and 2.
The detecting unit 10 of a flow meter has a casing consisting of a body 12 and a cover 14 fixed to the body 12 with bolts. A cup-formed partition member 16 is disposed within the casing. The interior of the partition member 16 and a space extending above the partition member 16 form an upstream space 18, while the exterior of the partition member 16 and a space extending below the partition member 16 form a downstream space 20. An inlet 22 to be connected to .~,.;
- ' .
~;98~0 a measured system communicates with the upper part of the upstream space 18 through a cylindrical screen 24, a liquid sump 15 formed by the member 13 and the introducing channel 17. A liquid discharging port 26 is formed in the lower part of the downstream space 20. The liquid discharging - 5a -,~
1~598~0 port 26 communicates with an outlet 28 by means of an up-right passage.
The upstream space 18 and the downstream space 20 communicates by means of a through hole 30 formed in the partition member 16 at the upper end thereof. In use, an automatic discharge valve, such as a float valve, not shown, is provided at the outlet 28 to maintain the downstream space 20 at the same pressure as that of the upstream space 18. The partition member 16 is provided further with an orifice 32 and a weir 34 in the surrounding wall thereof.
The shape of the weir 34 is decided by first speci-fying values for the flow rate measuring accuracy and the flow rate at a liquid level corresponding to the bottom of the weir, secondaly designing an orifice which provides the specified flow rate at a liquid level corresponding to the bottom of the weir and a flow rate measuring accuracy not greater than the specified value, and thirdly, assuming that the weir consists of a plurality of rectangular orifices each of a fixed minute height piled up one over the other, deciding the respective widths of the rectangular orifices so that the ratio of an increment of flow rate given by placing a rectangular orifice to the total flow rate co-incides with the specified flow rate measuring accuracy.
An exemplary procedure of designing the weir 34 will be described hereunder. Suppose that the flow rate meas-~Z598~) uring accuracy is 2%, the diameter of the orifice 32 is 5mm,and the distance from the orifice to the lower end of the weir 34 is 12.4mm. Then, water flows out through the orifice 32 at a flow rate of 20.91 kg/hr when the liquid level co-incides with the bottom of the weir 34. The calculated values for the height (mm) of the weir 34 (the height of the liquid level from the bottom of the weir 34), the width (mm) of the weir, and the flow rate (kg/hr) are tabulated in Table 1.
Table 1 Height (mm)Width (mm)Flow rate (kg/hr) 1 0.23 21.75
The applicant of the present application has been engaged in the development of a flow meter employing a so-called proportional weir in which the flow rate of the liquid is proportional to the liquid level on the upstream side of the weir. The interior space of the casing of this flow meter is pàrtitioned by a vertical wall into an-up-stream space having an inlet formed in the upper part of the same and connecting to the measured system, and a downstream space having a liquid discharge port formed in the lower part of the same, the upstream space and the downstream space communicate with each other by means of a space above the partition wall, a float valve capable of automatically dis-charge the liquid is provided at the liquid discharging port, and the liquid level in the upstream space is measured with a float or the like. Since the flow rate of a liquid ;; --1--.
that flows through an orifice is proportional to the square root of the distance from the liquid surface to the orifice, the proportional weir is a vertically elongate slit decreas-ing upward in width.
The flow rate measuring accuracy of the above-mentioned proportional weir reduces with the decrease of the flow rate, because the measuring error in measuring the liquid level in the upstream space is caused by the turbulence of the liquid surface and/or the resistance between the contact surfaces of the sliding members of a mechanism for con-verting the displacement of the float into the correspond-ing electric signal and those factors causative of the measuring error are constant regardless of the liquid level, and hence the de'gree of the influence of those factors causative of the measuring error on the measuring accuracy i6 enhanced as the flow rate decreases.
It is a technical subject of the present invention to provide a so-called constant-accuracy weir in which the ratio of the variation of the flow rate to the variation of the liquid level is reduced as the flow rate decreases and thereby the flow rate can be measured with constant measuring accuracy regardless of the liquid level, by turn-ing into account a fact that the liquid level measuring .; -2-1~59~3;~() error is practically constant regardless of the liquid level.
The technical means of the present invention taken to solve the above-mentioned technical problems comprises a weir of a shape designed so that the ratio of the variation of the flow rate caused by a fixed variation of the liquid level to the total flow rate at the existing liquid level is constant regardless of the liquid level.
The width of the weir is decided through the following numerical calculations. First, values for the flow rate measuring accuracy and the flow rate at a liquid level cor-responding to the bottom of the weir are specified. Secondly, an orifice which provides the specified flow rate at the liquid level corresponding to the bottom of the weir and a flow rate meas`uring accuracy not greater than the speci-fied value is designed. Thirdly, assuming that the weir consists of a plurality of rectangular orifices each of a fixed minute height piled up one over the other, the res-pective widths of the rectangular orifices are decided so that the ratio of an increment of flow rate given by placing a rectangular orifice to the total flow rate coincides with the specified flow rate measuring accuracy.
1~598c:0 The functions of the above-mentioned technical means are as follows. The liquid flows through the inlet into the upstream space defined by the partition wall, them flows through the orifice and the weir into the downstream space, and then flows outside through the outlet. Since the re-lation between the liquid level in the upstream space and the flow rate at the weir is known, the flow rate at the weir is obtained on the basis of the measured liquid level.
The ratio of the increment or decrement of the flow rate for a fixed variation of the liquid level to the total flow rate is constant and coincides with the specified measuring accuracy, as far as the range of the variation of the liquid level in the upstream space is within the height of the weir. On the other hand, liquid level measuring error is practically constant as in the conventional liquid levei mea~urement, regardless of the liquid level. Accordingly, the flow rate measuring accuracy is constant regardless of the liquid level.
The characteristic effects of the present invention are as follows. Since the flow rate measuring accuracy of the flow meter of the present invention is constant re-gardless of the liquid level, the flow meter of the present invention is capable of accurately measuring the flow rate ~259820 regardless of the flow rate or the variation of the flow rate.
In a constant-accuracy weir employed in the present invention, the flow rate varies as an expo-nential function of the liquid level, therefore, the constant-accuracy weir has a flow rate measuring range far wider than that of a conventional propor-tional weir of the same height.
In the drawings:
Figure 1 is a sectional view of the detect-ing unit of a flow meter, in a preferred embodiment, according to the present invention; and Figure 2 is an end view of an exemplary weir according to the present invention, and a graph showing the relation between the height of the liquid level at the weir and the flow rate.
A preferred embodiment of the above-mentioned technical means will be described hereinafter in con-nection with Figs. 1 and 2.
The detecting unit 10 of a flow meter has a casing consisting of a body 12 and a cover 14 fixed to the body 12 with bolts. A cup-formed partition member 16 is disposed within the casing. The interior of the partition member 16 and a space extending above the partition member 16 form an upstream space 18, while the exterior of the partition member 16 and a space extending below the partition member 16 form a downstream space 20. An inlet 22 to be connected to .~,.;
- ' .
~;98~0 a measured system communicates with the upper part of the upstream space 18 through a cylindrical screen 24, a liquid sump 15 formed by the member 13 and the introducing channel 17. A liquid discharging port 26 is formed in the lower part of the downstream space 20. The liquid discharging - 5a -,~
1~598~0 port 26 communicates with an outlet 28 by means of an up-right passage.
The upstream space 18 and the downstream space 20 communicates by means of a through hole 30 formed in the partition member 16 at the upper end thereof. In use, an automatic discharge valve, such as a float valve, not shown, is provided at the outlet 28 to maintain the downstream space 20 at the same pressure as that of the upstream space 18. The partition member 16 is provided further with an orifice 32 and a weir 34 in the surrounding wall thereof.
The shape of the weir 34 is decided by first speci-fying values for the flow rate measuring accuracy and the flow rate at a liquid level corresponding to the bottom of the weir, secondaly designing an orifice which provides the specified flow rate at a liquid level corresponding to the bottom of the weir and a flow rate measuring accuracy not greater than the specified value, and thirdly, assuming that the weir consists of a plurality of rectangular orifices each of a fixed minute height piled up one over the other, deciding the respective widths of the rectangular orifices so that the ratio of an increment of flow rate given by placing a rectangular orifice to the total flow rate co-incides with the specified flow rate measuring accuracy.
An exemplary procedure of designing the weir 34 will be described hereunder. Suppose that the flow rate meas-~Z598~) uring accuracy is 2%, the diameter of the orifice 32 is 5mm,and the distance from the orifice to the lower end of the weir 34 is 12.4mm. Then, water flows out through the orifice 32 at a flow rate of 20.91 kg/hr when the liquid level co-incides with the bottom of the weir 34. The calculated values for the height (mm) of the weir 34 (the height of the liquid level from the bottom of the weir 34), the width (mm) of the weir, and the flow rate (kg/hr) are tabulated in Table 1.
Table 1 Height (mm)Width (mm)Flow rate (kg/hr) 1 0.23 21.75
2 0.34 22.63
3 0.42 23.55
4 0.49 24.50 0.55 25.49 0.80 31.07 1.30 46.17 1.97 68.60 2.95 101.94 4.40 151.47 6.55 225.08 9.73 334.45 14.47 496.97 1~598~0 21.50 738.48 100 31.95 1097.33 Eig. 2 shows the respective shapes of the orifice 32 and the weir 34 decided on the basis of the data of Table 1, and a graph showing the plot of the data of Table 1 in the relation of the flow rate (Q) to the height ~H) of the weir 34. The referring number 43 shows a connector for wiring.
An insulation plate 36, supporting member 38 and 40 are mounted on top of the cover 14. A potentiometer 42 is disposed at the center of the supooting member 40. The potentiometer 42 is covered with a protective cap 44. Elec-tric wiring and terminals, not shown, are provided within the protective cap 44.
A pipe 46 of a thin wall is extended downward from the potentiometer so as to penetrate through the cover 14 hermetically and reach to the central part of the bottom of the partition member 16. A pipe 50 penetrating through and fixed to a hollow spherical float 48 is fitted slidably on the pipe 46. Magnets 52 and 56 are attached to the pipe 50 of the float 48 and the actuator rod 54 of the potentio-meter 42 respectively.
The float 48 is provided with vanes 49. An inverted U-tube 51 is arranged at the liquid sump 15, extending ~X59820 downward. One end of the U-tube 53 reaches the level of the vanes 49, when the float 48 rests at the bottom, being directed tangentially.
The liquid level is measured in the following manner.
The float 48 rises and falls according to the variation of the liquid level in the upstream space 18. Then, the actuator rod 54 is displaced according to the movement of the float 48 by the interactions of the magnets 52 and 56. The dis-placement of the actuator rod 54 is converted into the corresponding electric signal by the potentiometer 42.
Thus the liquid level in the upstream space 18 is indicated by an electric signal.
If the flow rate is small, liquid from the inlet 22 is accumulated in the sump 15, flows down intermittently through the inverted U-tube 51 and strikes the vanes 49 to rotate the float 48. If the flow rate is large, liquid flows through the introducing channel 17 too and into the upstream space 18 tangentially around the float 48 to rotate the liquid therein. Since the float 48 accordingly rotates, the float 48 can move up and down smoothly depending upon the liquid level.
The flow meter needs parts for calculating the flow rate on the basis of the liquid level detected in the above-mentioned manner and for displaying the calculated result, however, since those parts are those of well-known techniques, the description thereof will be omitted.
; _9_ 1;~598~0 Figure 1 is a sectional view of the detecting unit of a flow meter, in a preferred embodiment, according to the present invention; and Figure 2 is an end view of an exemplary weir according to the present invention, and a graph showing the relation between the height of the liquid level at the weir and the flow rate.
An insulation plate 36, supporting member 38 and 40 are mounted on top of the cover 14. A potentiometer 42 is disposed at the center of the supooting member 40. The potentiometer 42 is covered with a protective cap 44. Elec-tric wiring and terminals, not shown, are provided within the protective cap 44.
A pipe 46 of a thin wall is extended downward from the potentiometer so as to penetrate through the cover 14 hermetically and reach to the central part of the bottom of the partition member 16. A pipe 50 penetrating through and fixed to a hollow spherical float 48 is fitted slidably on the pipe 46. Magnets 52 and 56 are attached to the pipe 50 of the float 48 and the actuator rod 54 of the potentio-meter 42 respectively.
The float 48 is provided with vanes 49. An inverted U-tube 51 is arranged at the liquid sump 15, extending ~X59820 downward. One end of the U-tube 53 reaches the level of the vanes 49, when the float 48 rests at the bottom, being directed tangentially.
The liquid level is measured in the following manner.
The float 48 rises and falls according to the variation of the liquid level in the upstream space 18. Then, the actuator rod 54 is displaced according to the movement of the float 48 by the interactions of the magnets 52 and 56. The dis-placement of the actuator rod 54 is converted into the corresponding electric signal by the potentiometer 42.
Thus the liquid level in the upstream space 18 is indicated by an electric signal.
If the flow rate is small, liquid from the inlet 22 is accumulated in the sump 15, flows down intermittently through the inverted U-tube 51 and strikes the vanes 49 to rotate the float 48. If the flow rate is large, liquid flows through the introducing channel 17 too and into the upstream space 18 tangentially around the float 48 to rotate the liquid therein. Since the float 48 accordingly rotates, the float 48 can move up and down smoothly depending upon the liquid level.
The flow meter needs parts for calculating the flow rate on the basis of the liquid level detected in the above-mentioned manner and for displaying the calculated result, however, since those parts are those of well-known techniques, the description thereof will be omitted.
; _9_ 1;~598~0 Figure 1 is a sectional view of the detecting unit of a flow meter, in a preferred embodiment, according to the present invention; and Figure 2 is an end view of an exemplary weir according to the present invention, and a graph showing the relation between the height of the liquid level at the weir and the flow rate.
Claims (6)
1. A flow meter for measuring the flow rate of a liquid comprising a vertically elongated slit weir arranged to have said liquid flow therethrough and defining an upstream space on one side thereof, said flow meter being capable of detecting the liquid level in said upstream space with respect to said weir and determining the flow rate of the liquid on the basis of the relationship between said liquid level and the flow rate of the liquid that flows through the weir, wherein a width of said weir is designed so that a constant percentage variation in total flow rate causes a constant variation in liquid level at any liquid level.
2. A flow meter according to Claim 1, wherein said weir comprises a vertically elongated slit upwardly increasing in width.
3. A flow meter according to Claim 2, wherein said weir has a lower section tapering to a lower end at which flow through said weir terminates and wherein said flow meter further comprises an orifice through which liquid flow occurs, said orifice having a predetermined diameter and being spaced a predeter-mined distance from said lower end of said weir, said predetermined distance and said predetermined diameter being determined to provide a desired flow rate when the liquid level in said upstream space is at or below said lower end of said weir.
4. A flow meter according to claim 3 having a flow rate measuring accuracy of 2%, wherein said predetermined diameter of said orifice is 5 mm, where-in said predetermined distance is 12.4 mm and wherein the flow rate through said orifice is 20.91 kg/hr when the liquid level coincides with said lower end of said weir.
5. A flow meter according to claim 3, wherein said weir comprises a specific width dimension at each level of height above said lower end thereof, in accordance with the following table wherein Column 1 sets forth each height dimension and Column II sets forth the corresponding width dimension with the flow rate for a liquid level at each of the height dimen-sions set forth in Column 1 being indicated in Column III
6. A method for forming the shape of a weir in a flow meter for measuring the flow rate of a liquid having said weir arranged therein and defining an upstream space on one side of said weir, said weir being shaped as a vertically elongated slit having a lower section tapering to a lower end to which flow through said weir terminates, with said flow meter further comprising an orifice through which liquid flow occurs, said orifice having a predetermined diameter and being spaced a predetermined distance from said lower end of said weir, said method com-prising the steps of specifying values for the flow rate measuring accuracy of said meter and the flow rate at a liquid level corresponding to said lower end of said weir, designing said orifice to provide said specified flow rate at a liquid level corres-ponding to said lower end of said weir and a flow rate measuring accuracy not greater than said speci-fied value and, assuming that said weir consists of a plurality of rectangular orifices, each of a fixed minute height arranged one over the other, determining the respective widths of said rectangular orifices so that a given ratio of an incremental change of flow rate to the total flow rate produces a constant change in level at any liquid level.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000490285A CA1259820A (en) | 1985-09-10 | 1985-09-10 | Flow meter for measuring the flow rate of liquid |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000490285A CA1259820A (en) | 1985-09-10 | 1985-09-10 | Flow meter for measuring the flow rate of liquid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1259820A true CA1259820A (en) | 1989-09-26 |
Family
ID=4131350
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000490285A Expired CA1259820A (en) | 1985-09-10 | 1985-09-10 | Flow meter for measuring the flow rate of liquid |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1259820A (en) |
-
1985
- 1985-09-10 CA CA000490285A patent/CA1259820A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |