JP3757009B2

JP3757009B2 - Split flow meter

Info

Publication number: JP3757009B2
Application number: JP28342696A
Authority: JP
Inventors: 一平鳥越
Original assignee: 一平鳥越
Priority date: 1996-10-03
Filing date: 1996-10-03
Publication date: 2006-03-22
Anticipated expiration: 2016-10-03
Also published as: JPH10111156A

Description

【０００１】
【産業上の利用分野】
本発明は、管内を流れる流体の流量を測定する装置、とくに主管内の流れを分流管に分流し、分流管を流れる流量と、分流管と主管の接続部の上流側と下流側の間の主管内差圧とから、主管内の流量を推定する分流式流量計に係わる。
【０００２】
【従来の技術】
主管の流れを分流管に分流して、分流管内の流量を測定し、主管内の流量と分流管内の流量の比―分流比を分流管内の流量に乗じて主管内の流量を知る分流式流量計は、主管の管径が大きく流量計を直接取り付けるのが困難である場合や、流量計を主管に直接取り付けると流量計の保守維持が困難になる場合等に有効な流量測定方式である。分流管に分流することにより、測定すべき流量が小さくなって流量計のコストが低くなること、流量計の設置条件の自由度が大きくなること、主管ではなく分流管に流量計を設置することで、主管の圧力損失を小さくできること等の利点も有している。
【０００３】
【発明が解決しようとする課題】
しかしながら、分流式流量計においては、原理上、分流比が既知でなくてはならない。ところが、分流比は、一定ではなく流れの条件によって変化する。一般に、流れの条件が変化した場合、主管と分流管の流体抵抗が異なる変化をするためである。このため、従来の分流式流量計には、流れの条件が予め分かっていて分流比の変化も予め分かっている場合や、流れの条件の変化範囲が小さい場合にしか、正しく流量を測定できないという問題点がある。常に一定の分流比を保つよう工夫をした分流式流量計もあるが、この型の分流式流量計では、主管に絞りを挿入したりフィードバック機構を導入したりしているため、上述の分流式流量計本来の利点を損なうことになる。
【０００４】
【課題を解決するための手段】
分流比が変化しても正しく主管内流量が測定できる分流式流量計を実現するため、本発明においては、主管内の流れを分流管に分流して、分流管と主管の接続部の上流側と下流側の間で主管内差圧を測定し、この差圧出力を用いて分流比を計算し、分流管内の流量に分流比を乗ずることにより主管内の流量を推定する。
【０００５】
【作用】
主管の流れの一部を分流管に分流すると、主管内流量は、分流管の分岐点より下流では上流での流量より減少し、分流管の合流点で再び元の流量に復する。従って、分流管が主管と接続している点を境に、上流と下流とで主管内の流速が変化する。このとき、ベルヌーイの定理から、接続点の上流と下流には静圧差が生じ、その静圧差の大きさは主管内の流量と分流管内の流量の比─分流比に依存する。本発明の流量計においては、この静圧差を測定して分流比を計算し、分流管内の流量に分流比を乗じて主管内の流量を推定している。
【０００６】
分流管の接続点の上下流の差圧には、流体の粘性に起因する圧力降下の項もまた含まれている。ベルヌーイの定理から導出される上述の差圧項が、分流管の分岐点における差圧と合流点における差圧の両者中にノルマルモードの信号として含まれているのに対して、粘性に起因する圧力降下項は、コモンモードの雑音として含まれる。請求項２に記載の流量計においては、上記二つの差圧の差をとることによって、粘性に起因する圧力降下項を相殺し、流体の粘性の影響を受けることなく正確に分流比を計算することができる。
【０００７】
【実施例】
以下、本発明の詳細を実施例に基づいて説明する。図１は本発明の第一実施例である。図１において、１は、体積流量Ｑの流れている断面積Ｓの主管である。２は分流管で、上流側接続部１１および下流側接続部１２において主管１と接続している。３は分流管２に取り付けられた流量計である。４は差圧計で、導圧管６および６’によって導かれた主管内の静圧の差を測定している。導圧管６は、主管１と分流管２の上流側接続部１１より上流側の導圧口１３において、また導圧管６’は上流側接続部１１よりも下流で下流側接続部１２よりも上流の導圧口１４において、主管１に接続されている。８は、信号処理装置で、流量計３の出力および差圧計４の出力から、主管１内の流量を計算して、指示計器９に出力している。
【０００８】
本実施例では、流体が非圧縮・非粘性と近似できる場合を想定している。そこで、流れている流体を密度ρが一定で非粘性の流体と仮定して動作を説明する。分流管に分流している体積流量をｑとすると、主管１内の体積流量は、分流管２の上流側接続部１１より上流ではＱ、上流側接続部１１と下流側接続部１２の間ではＱ−ｑ、下流側接続部１２より下流では再びＱとなる。ここで、主管１の上流から下流に至る流線に沿って、ベルヌーイの定理を適用すれば、導圧口１３の断面における圧力をｐ₁₃、導圧口１４の断面における圧力をｐ₁₄として、
【０００９】
【数１】

【００１０】
が成り立つ。従って、差圧計４の出力Δｐ₄は
【００１１】
【数２】

【００１２】
となる。数２の両辺をρｑ²／Ｓ²で割って整理すると
【００１３】
【数３】

【００１４】
となる。主管１の断面積Ｓは一定の既知量であり、また密度ρも一定の既知量であるから、差圧計４の出力Δｐ₄と流量計３の出力ｑとが測定されれば、分流比Ｑ／ｑが計算できることが分かる。この分流比を流量計３の出力ｑに乗ずれば、主管１内の体積流量Ｑが知られる。
【００１５】
以上の原理から明らかなように、流量計３は、分流管内の流量を測定できるものであれば、どのような種類のものであっても構わない。また、本実施例においては、分流管２の上流側接続部１１の上流と下流の差圧を測定しているが、下流側接続部１２の上流と下流の差圧を測定しても、差圧の極性が反転する他は何ら原理上の違いは無い。
【００１６】
（第二実施例）第一実施例においては、流体を非粘性であると近似した。粘性の影響が小さい場合は、第一実施例の構成のままで、正確に主管１内流量を推定することができる。しかし、差圧計４の出力には数２の圧力の他に、粘性に起因する主管１内の圧力降下分が含まれるから、圧力降下が大きい場合には、数３で分流比を推定したのでは誤差が出る。この誤差を補正する構成をとったのが図２の第二実施例である。図２において、１は、体積流量Ｑの流れている断面積Ｓの主管である。２は分流管で、上流側接続部１１および下流側接続部１２において主管１と接続している。３は分流管２に取り付けられた流量計である。４は差圧計で、導圧管６および６’によって導かれた主管内の静圧の差を測定している。導圧管６は、主管１と分流管２の上流側接続部１１より上流側の導圧口１３において、また導圧管６’は、上流側接続部１１および下流側接続部１２から等距離にある断面内の導圧口１４において、主管１に接続されている。５は第二の差圧計で、導圧管７および７’によって導かれた主管内の静圧の差を測定している。導圧管７は、導圧管６’と共通の導圧口１４において、また導圧管７’は、下流側接続部１２より下流の導圧口１５において、主管１に接続されている。主管１の管軸に沿って測った、導圧口１３と１４の間の距離と、導圧口１４と１５との間の距離は、等しく作製されている。８は、信号処理装置で、流量計３の出力、差圧計４の出力、第二の差圧計５の出力、および別途測定された流体の密度ρとから、主管１内の流量を計算して、指示計器９に出力している。
【００１７】
分流管に流れている体積流量をｑとすると、主管１内の体積流量は、分流管２の上流側接続部１１より上流ではＱ、上流側接続部１１と下流側接続部１２の間ではＱ−ｑ、下流側接続部１２より下流ではＱとなる。ベルヌーイの定理から、導圧口１３の断面における圧力をｐ₁₃、導圧口１４の断面における圧力をｐ₁₄、導圧口１５の断面における圧力をｐ₁₅として、
【００１８】
【数４】

【００１９】
が成り立つ。差圧計４の出力Δｐ₄と第二の差圧計５の出力Δｐ₅は、数４から計算される差圧の他に、粘性による圧力降下分τ₄およびτ₅がそれぞれ重畳されて、
【００２０】
【数５】

【００２１】
【数６】

【００２２】
となる。本実施例では、導圧口１３と１４の間の距離と、導圧口１４と１５の間の距離が等しくなっており、なおかつ導圧口１４が接続部１１と１２のちょうど中央にあるから、τ₄とτ₅は互いに等しくなる。従って、Δｐ₄とΔｐ₅の差をとってΔｐ₀とすれば
【００２３】
【数７】

【００２４】
であり、Δｐ₀を使って、分流比が
【００２５】
【数８】

【００２６】
と計算できる。ここで、粘性による圧力降下の項τ₄およびτ₅は、互いに相殺され、分流比の計算に影響していない。なお、本実施例では、流体密度ρが変化する場合を想定して、密度ρを別途測定して、分流比の計算に用いている。
【００２７】
【発明の効果】
以上説明してきたように、本発明では、主管の流れを分流管に分流して分流流量を測定する他に、分流管と主管の接続部の上流側と下流側の主管内静圧差を測定し、この差圧を用いて分流比を正確に求め、主管内流量を測定する。流れの条件が変化して分流比が変化しても、正確に主管内流量を測定することのできる分流式流量計を実現できることは、本発明の特有の効果である。
【００２８】
また、他の接続部の上流側と下流側の静圧差を測定する差圧計を用いる流量計は、流体の粘性の影響が大きくて主管内に大きな圧力降下がある場合にも、その影響を受けることなく正確に分流比を計算できる。粘性の影響が大きい場合にも分流比を正確に求めることのできる分流式流量計を実現できることも、本発明の特有の効果である。
【図面の簡単な説明】
【図１】本発明の第一実施例である。
【図２】第二の差圧計を用いた、本発明の第二実施例である。
【符号の説明】
１主管
２分流管
３流量計
４差圧計
５第二の差圧計
６、６’ 導圧管
７、７’ 導圧管
８信号処理装置
９指示計器
１１上流側接続部
１２下流側接続部
１３、１４、１５導圧口[0001]
[Industrial application fields]
The present invention relates to an apparatus for measuring the flow rate of a fluid flowing in a pipe, in particular, the flow in the main pipe is divided into the flow dividing pipes, and the flow rate flowing through the flow dividing pipe is between The present invention relates to a shunt flow meter that estimates the flow rate in the main pipe from the differential pressure in the main pipe.
[0002]
[Prior art]
Dividing the main pipe flow into the diversion pipe, measuring the flow rate in the diversion pipe, and dividing the flow rate in the main pipe by multiplying the flow ratio in the diversion pipe by the ratio of the flow rate in the main pipe and the flow rate in the diversion pipe to the flow rate in the diversion pipe The meter is an effective flow measurement method when the main pipe has a large diameter and it is difficult to attach the flow meter directly, or when the flow meter is attached directly to the main pipe, it becomes difficult to maintain and maintain the flow meter. By diverting to the shunt pipe, the flow rate to be measured is reduced and the cost of the flow meter is reduced, the flexibility of installation conditions of the flow meter is increased, and the flow meter is installed in the shunt pipe instead of the main pipe Thus, there is an advantage that the pressure loss of the main pipe can be reduced.
[0003]
[Problems to be solved by the invention]
However, in a shunt flow meter, in principle, the shunt ratio must be known. However, the diversion ratio is not constant but varies depending on the flow conditions. In general, when the flow condition changes, the fluid resistance of the main pipe and the shunt pipe changes differently. For this reason, the conventional shunt flow meter can measure the flow rate correctly only when the flow conditions are known in advance and the change in the diversion ratio is also known in advance, or when the change range of the flow conditions is small. There is a problem. Although there is a shunt flow meter that is devised to always maintain a constant shunt ratio, this type of shunt flow meter inserts a throttle in the main pipe or introduces a feedback mechanism. The inherent advantages of the flow meter will be impaired.
[0004]
[Means for Solving the Problems]
In order to realize a shunt flow meter that can correctly measure the flow rate in the main pipe even if the shunt ratio changes, in the present invention, the flow in the main pipe is shunted into the shunt pipe, and the upstream side of the connection between the shunt pipe and the main pipe The flow rate in the main pipe is estimated by measuring the differential pressure in the main pipe between the downstream and the downstream side, calculating the diversion ratio using this differential pressure output, and multiplying the flow rate in the diversion pipe by the diversion ratio.
[0005]
[Action]
When a part of the flow of the main pipe is divided into the branch pipe, the flow rate in the main pipe decreases from the upstream flow rate downstream from the branch point of the split pipe, and returns to the original flow rate again at the junction point of the split pipe. Therefore, the flow velocity in the main pipe changes upstream and downstream at the point where the shunt pipe is connected to the main pipe. At this time, from Bernoulli's theorem, there is a static pressure difference upstream and downstream of the connection point, and the magnitude of the static pressure difference depends on the ratio of the flow rate in the main pipe to the flow rate in the shunt pipe. In the flowmeter of the present invention, this static pressure difference is measured to calculate the diversion ratio, and the flow rate in the main pipe is estimated by multiplying the flow rate in the diversion pipe by the diversion ratio.
[0006]
The differential pressure upstream and downstream of the junction of the shunt pipe also includes a pressure drop term due to fluid viscosity. The above-mentioned differential pressure term derived from Bernoulli's theorem is included as a normal mode signal in both the differential pressure at the branch point of the diversion pipe and the differential pressure at the confluence. The pressure drop term is included as common mode noise. In the flowmeter according to claim 2, by taking the difference between the two differential pressures, the pressure drop term due to the viscosity is canceled out, and the shunt ratio is accurately calculated without being affected by the viscosity of the fluid. be able to.
[0007]
【Example】
Hereinafter, details of the present invention will be described based on examples. FIG. 1 shows a first embodiment of the present invention. In FIG. 1, 1 is a main pipe having a cross-sectional area S in which a volume flow rate Q flows. Reference numeral 2 denotes a shunt pipe, which is connected to the main pipe 1 at the upstream connection portion 11 and the downstream connection portion 12. Reference numeral 3 denotes a flow meter attached to the shunt pipe 2. A differential pressure gauge 4 measures the difference in static pressure in the main pipe guided by the pressure guiding pipes 6 and 6 '. The pressure guiding pipe 6 is at a pressure guiding port 13 upstream of the upstream connecting portion 11 of the main pipe 1 and the branch pipe 2, and the pressure guiding pipe 6 ′ is downstream of the upstream connecting portion 11 and upstream of the downstream connecting portion 12. The pressure guiding port 14 is connected to the main pipe 1. A signal processing device 8 calculates the flow rate in the main pipe 1 from the output of the flow meter 3 and the output of the differential pressure meter 4 and outputs the flow rate to the indicating instrument 9.
[0008]
In this embodiment, it is assumed that the fluid can be approximated to non-compressed and non-viscous. Therefore, the operation will be described assuming that the flowing fluid is a non-viscous fluid with a constant density ρ. If the volume flow rate divided into the flow dividing pipe is q, the volume flow rate in the main pipe 1 is Q upstream of the upstream connection portion 11 of the flow dividing pipe 2 and between the upstream connection portion 11 and the downstream connection portion 12. Q-q is again Q downstream from the downstream connection portion 12. Here, along the flow line leading from upstream to downstream of the main pipe 1, by applying the Bernoulli's principle, the pressure in the cross section of the guide pressure port 13 a pressure in p _13, conductive pressure port 14 of the cross-section as p _14,
[0009]
[Expression 1]

[0010]
Holds. Therefore, the output Δp ₄ of the differential pressure gauge 4 is
[Expression 2]

[0012]
It becomes. When dividing both sides of Equation ² by ρq ² / S ² ,
[Equation 3]

[0014]
It becomes. Since the cross-sectional area S of the main pipe 1 is a constant known amount and the density ρ is also a constant known amount, if the output Δp ₄ of the differential pressure gauge ₄ and the output q of the flow meter 3 are measured, the flow dividing ratio Q It can be seen that / q can be calculated. If this diversion ratio is multiplied by the output q of the flow meter 3, the volume flow rate Q in the main pipe 1 is known.
[0015]
As is apparent from the above principle, the flow meter 3 may be of any type as long as it can measure the flow rate in the shunt pipe. In this embodiment, the differential pressure upstream and downstream of the upstream connection portion 11 of the flow dividing pipe 2 is measured. However, even if the differential pressure upstream and downstream of the downstream connection portion 12 is measured, the differential pressure is different. There is no difference in principle except that the polarity of the pressure is reversed.
[0016]
(Second Embodiment) In the first embodiment, the fluid was approximated to be non-viscous. When the influence of the viscosity is small, the flow rate in the main pipe 1 can be accurately estimated with the configuration of the first embodiment. However, since the output of the differential pressure gauge 4 includes the pressure drop in the main pipe 1 due to viscosity in addition to the pressure of Formula 2, when the pressure drop is large, the shunt ratio was estimated by Formula 3. Then there is an error. The second embodiment of FIG. 2 adopts a configuration for correcting this error. In FIG. 2, reference numeral 1 denotes a main pipe having a cross-sectional area S in which a volume flow rate Q flows. Reference numeral 2 denotes a shunt pipe, which is connected to the main pipe 1 at the upstream connection portion 11 and the downstream connection portion 12. Reference numeral 3 denotes a flow meter attached to the shunt pipe 2. A differential pressure gauge 4 measures the difference in static pressure in the main pipe guided by the pressure guiding pipes 6 and 6 '. The pressure guiding pipe 6 is at a pressure guiding port 13 upstream of the upstream connecting portion 11 of the main pipe 1 and the flow dividing pipe 2, and the pressure guiding tube 6 ′ is equidistant from the upstream connecting portion 11 and the downstream connecting portion 12. The pressure guide port 14 in the cross section is connected to the main pipe 1. A second differential pressure gauge 5 measures the difference in static pressure in the main pipe guided by the pressure guiding pipes 7 and 7 '. The pressure guiding tube 7 is connected to the main tube 1 at a pressure guiding port 14 common to the pressure guiding tube 6 ′, and the pressure guiding tube 7 ′ is connected to the pressure guiding port 15 downstream from the downstream side connecting portion 12. The distance between the

pressure inlets

13 and 14 and the distance between the

pressure inlets

14 and 15 measured along the tube axis of the main pipe 1 are made equal. 8 is a signal processing device that calculates the flow rate in the main pipe 1 from the output of the flow meter 3, the output of the differential pressure meter 4, the output of the second differential pressure meter 5, and the separately measured fluid density ρ. Is output to the indicating instrument 9.
[0017]
Assuming that the volume flow rate flowing in the shunt pipe is q, the volume flow rate in the main pipe 1 is Q upstream of the upstream connection portion 11 of the shunt pipe 2 and Q between the upstream connection portion 11 and the downstream connection portion 12. −q, Q downstream from the downstream side connection portion 12 From Bernoulli's theorem, the pressure in the cross section of the pressure inlet 13 is p ₁₃ , the pressure in the cross section of the pressure inlet 14 is p ₁₄ , and the pressure in the cross section of the pressure inlet 15 is p ₁₅ ,
[0018]
[Expression 4]

[0019]
Holds. An output Delta] p ₄ of the differential pressure gauge 4 outputs Delta] p ₅ of the second differential pressure gauge 5, in addition to the differential pressure is calculated from Equation 4, the pressure drop tau ₄ and tau ₅ due to viscosity is superimposed respectively,
[0020]
[Equation 5]

[0021]
[Formula 6]

[0022]
It becomes. In this embodiment, the distance between the

pressure inlets

13 and 14 and the distance between the

pressure inlets

14 and 15 are equal, and the pressure inlet 14 is just in the center of the connecting

portions

11 and 12. , Τ ₄ and τ ₅ are equal to each other. Therefore, if the difference between Δp ₄ and Δp ₅ is taken as Δp ₀ ,
[Expression 7]

[0024]
Using Δp ₀ , the shunt ratio is
[Equation 8]

[0026]
Can be calculated. Here, the pressure drop terms τ ₄ and τ ₅ due to viscosity cancel each other and do not affect the calculation of the diversion ratio. In the present embodiment, assuming that the fluid density ρ changes, the density ρ is separately measured and used for the calculation of the diversion ratio.
[0027]
【The invention's effect】
As described above, in the present invention, the flow of the main pipe is divided into the diversion pipes to measure the diversion flow rate, and the static pressure difference in the main pipe at the upstream side and the downstream side of the connection portion between the diversion pipe and the main pipe is measured. Using this differential pressure, the flow ratio is accurately determined and the flow rate in the main pipe is measured. It is a unique effect of the present invention that a shunt flow meter that can accurately measure the flow rate in the main pipe can be realized even if the shunt ratio changes due to changes in the flow conditions.
[0028]
In addition, a flow meter that uses a differential pressure gauge that measures the difference in static pressure between the upstream side and the downstream side of other connections is also affected when there is a large pressure drop in the main pipe due to the effect of fluid viscosity. The shunt ratio can be calculated accurately without any problem. It is a unique effect of the present invention that a shunt flow meter capable of accurately obtaining a shunt ratio even when the influence of viscosity is large can be realized.
[Brief description of the drawings]
FIG. 1 is a first embodiment of the present invention.
FIG. 2 is a second embodiment of the present invention using a second differential pressure gauge.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Main pipe 2 Dividing pipe 3 Flowmeter 4 Differential pressure gauge 5 Second differential pressure gauge 6, 6 'Pressure guiding pipe 7, 7' Pressure guiding pipe 8 Signal processing device 9 Indicator meter 11 Upstream side connection part 12 Downstream

side connection parts

13, 14 15 Pressure inlet

Claims

In a flow dividing type flow meter for diverting the flow of the main pipe (1) to the diversion pipe (2) and estimating the flow rate in the main pipe from the flow rate in the diversion pipe, one connection part (11) between the diversion pipe and the main pipe A differential pressure gauge (4) for measuring the difference in static pressure in the main pipe between the upstream side and the downstream side of the pipe, and the flow rate in the main pipe is estimated from the static pressure difference obtained from the differential pressure gauge and the flow rate in the shunt pipe A shunt flow meter characterized by

Another connecting part (12) of the main pipe (1) and the flow dividing pipe (2) and a differential pressure gauge (5) for measuring the static pressure difference in the main pipe between the upstream side and the downstream side of the connecting part (12) The shunt flow meter according to claim 1, wherein the error is corrected by using the output of the differential pressure gauge (5).