JP3565374B2

JP3565374B2 - Current meter

Info

Publication number: JP3565374B2
Application number: JP14287695A
Authority: JP
Inventors: 馨磯本
Original assignee: 石川島播磨重工業株式会社
Priority date: 1995-06-09
Filing date: 1995-06-09
Publication date: 2004-09-15
Anticipated expiration: 2019-09-15
Also published as: JPH08334527A

Description

【０００１】
【産業上の利用分野】
本発明は、流体の速度を計測する流速計に関する。
【０００２】
【従来の技術】
流体の流速を計測する計測器としては、ピトー管が用いられる。ピトー管は前面で静圧と動圧からなる全圧を計測し、側面で静圧を計測して動圧を求め、これより流速を求める。しかし、流速が低いときには動圧が小さいため全圧と静圧との比が小さく測定誤差が大きい。ところで、計器の背面の背圧と全圧との比は流速が小さくても大きな値が得られる。そこで背圧を用いた流速計が用いられている。
【０００３】
図３は全圧と背圧を用いた流速計の一例を示す図である。（Ａ）は縦断面図を示し、（Ｂ）は（Ａ）のＹ−Ｙ断面図である。矢印は流体の流れ方向示す。流速計１の断面は長円形で、長軸を流れに平行に設置する。前面に全圧取入口２が複数あり、後部の同じレベルに背圧取入口３が設けられ、全圧（ＰＴ）、背圧（ＰＢ）の平均値を求め、全圧と背圧の比と他の方法で求めた流速とから較正曲線を作成し、実測した全圧と背圧からこの較正曲線を用いて流速を算出する。これにより、比較的低速度まで精度よく測定することができる。
【０００４】
【発明が解決しようとする課題】
ピトー管や図３に示した全圧と背圧を用いた流速計は、流れの向きを固定とし、この方向に合わせて流速計を設定する。このため、流れの向きが変化する位置では計測できない。図４は図３に示した流速計の較正曲線の一例を示す。縦軸は全圧／背圧比を示し、横軸は流速を示す。流速計の断面は長円形であり、レイノルズ数（主に流速）によって流速計まわりの流れが層流から乱流になるなど流れの性質が急変する値があり、較正曲線に不連続点が発生する。このため限られた範囲のレイノルズ数でしか使用できない。
【０００５】
本発明は上述の問題点に鑑みてなされたもので、流れの向きの変化に対応し精度よく計測できる流速計を提供することを目的とする。また、低流速域まで精度よく計測できる流速計を提供することを目的とする。
【０００６】
【課題を解決するための手段】
上記目的を達成するため、請求項１の発明では、二等辺三角形で二等辺の交点を頂部とし頂部の対辺を底部とするくさび型断面形状を有し頂部で全圧を測定し底部で背圧を測定する測定部と、該測定部をくさび型断面に垂直な軸まわりに回転自在に支持する支持部とからなり、前記測定部の回転中心は測定部の前記垂直な軸に平行な軸まわりの回転モーメントの中心よりも頂部側に設けられることより前記頂部は流体の流れ方向に常に正対するように回転する。
【０００７】
請求項２の発明では、前記測定部には流体の温度を計測する温度センサが設けられている。
【０００８】
請求項３の発明では、前記支持部には前記測定部の回転角度を検出する回転角度検出器が設けられている。
【０００９】
請求項４の発明では、前記支持部には前記測定部で測定した全圧、背圧、温度および較正データから流体の流速を算出する演算部を備えている。
【００１０】
【作用】
請求項１の発明では、くさびの頂部が流れ方向に正対している場合、くさびの頂部の全圧と底部の背圧の比または差はレイノルズ数に対して安定しており、図４で説明したような不連続点は発生しない。背圧はピトー管などで計測される側圧よりも低い値まで計測できるので、この背圧を用いることにより低速でも精度よく計測できる。また、測定部の回転中心は測定部の前記垂直な軸に平行な軸まわりの回転モーメントの中心よりも頂部側に設けられているので、頂部は流れに対して正対するように回転する。これにより流れの方向が変化しても流れに正対して測定部が回転するので常に正確な計測が可能となる。
【００１１】
請求項２の発明では、測定部には流体の温度を計測する温度センサが設けられているので、計測値を温度補正して正確な流速が得られる。
【００１２】
請求項３の発明では、前記支持部には前記測定部の回転角度を検出する回転角度検出器が設けられているので、流れの向きを計測することができる。
【００１３】
請求項４の発明では、前記支持部には前記測定部で測定した全圧、背圧、温度および較正データから流体の流速を算出する演算部を備えているので、流速値が電気信号として出力され、使い易い流速計となっている。
【００１４】
【実施例】
以下、本発明の実施例について図面を参照して説明する。
図１は実施例の構成を示す図で、（Ａ）は平面図、（Ｂ）は（Ａ）のＸ−Ｘ断面図である。流速計１０は流体の全圧と背圧および温度を計測する測定部１１と測定部１１を回転可能に支持する支持部１２からなる。測定部１１は二等辺三角形で二等辺の交点を頂部とし頂部の対辺を底部とするくさび形状をしており、頂部は丸みをおび流体の全圧を測定する全圧取入口１３が設けられ、底部には背圧を測定する背圧取入口１４がくさび中心線Ｃ上に設けられている。くさび形状は二等辺三角形なのでくさび中心線Ｃに対して対称となっている。なお、全圧取入口１３と背圧取入口１４をそれぞれ複数設け、図３と同様に連通させ、平均値を求めるようにしてもよい。全圧取入口１３と背圧取入口１４はそれぞれ圧力センサ１５に導通しており、圧力センサ１５は全圧と背圧を計測する。全圧取入口１３近傍に検出端を有する温度センサ１６が設けられ、流体の温度を測定する。
【００１５】
図１（Ａ）の平面図に垂直方向に設けられた支持軸１７により測定部１１は回転可能に支持される。支持軸１７は測定部１１に固定され一体として回転し、支持部１２に設けられた軸受１８により回転可能に軸支される。なお流体が液体の場合は軸受部はシール構造とする。Ｒは支持軸１７の回転中心を示す。Ｇは測定部１１の支持軸１７に平行な軸まわりの回転モーメントの中心を示す。回転中心Ｒは回転モーメントの中心Ｇよりもくさびの頂部側に設けられている。これにより矢印で示す方向を流れ方向とすると、測定部１１のくさびの頂部は流れの方向に正対するように回転する。これにより流れの方向とくさび中心線Ｃが常に一致するようになる。
【００１６】
支持部１２は円筒形で軸受により支持軸１７を回転可能に軸支する。支持軸１７の回転角度を検出する回転角度検出器１９が設けられ、測定部１１の回転角を検出することにより支持部１２に対する流れの方向を検出することができる。なお、支持軸１７は中空とし圧力センサ１５と温度センサ１６の電線を通過できるようにする。
【００１７】
支持部１２には演算部２０が設けられ、全圧、背圧および温度の計測値と較正データから流体の流速を算出する。較正データは、例えば、図４に示したように全圧／背圧比に対する流速を表す表とする。入出力ライン２１は圧力センサ１５、温度センサ１６、回転角度検出器１９および演算部２０への電源供給と測定値および算出した流速等の出力をする。
【００１８】
図２は断面形状をパラメータとしたレイノルズ数に対する抵抗係数の変化を示す。長方形、くさび、長円および略円形を矢印で示す流れ方向の流体に入れた場合で、長方形とくさびは流速（レイノルズ数は流速に対応）が変化しても抵抗係数はあまり変化しない。一方長円と略円形はある流速を過ぎると抵抗係数が大きく変化する。抵抗係数が大きく変化するのは流れの性質が、例えば、層流から乱流になるというように変化したことを示す。流れの性質が変化すると図４で示したように較正曲線が不連続になる。長方形は抵抗係数の変化は少ないが、抵抗係数が大きい。くさびは流速の変化に対して抵抗係数の変化が少なく、抵抗係数も小さい。このため較正曲線にも不連続点が生ぜず、広い範囲の流速の測定に適した計測部の断面形状であることがわかる。
【００１９】
【発明の効果】
以上の説明から明らかなように、本発明は測定部をくさび型としくさびの頂部で全圧を測定し底部で背圧を測定して流速を算出する。背圧はピトー管等で測定する側圧よりも低いため、低速まで精度よく測定することが可能となる。また、くさびに対する流体の流れは流速が変化しても流れの性質が変わらないため、全圧、背圧より流速を算出するとき用いる較正曲線に不連続点が生ぜず、広い範囲の流速を計測することができる。さらに、測定部の回転中心を測定部の回転モーメント中心よりくさびの頂部側に配置することにより、頂部が流体の流れ方向に常に正対するようになる。これにより流れの向きが不明な場所に設置しても常に正しい計測が可能となると共に、流れの方向を測定することができる。
【図面の簡単な説明】
【図１】本発明の実施例の構成を示す図で、（Ａ）は平面図、（Ｂ）は（Ａ）のＸ−Ｘ断面図である。
【図２】測定部の断面形状としてくさび形状が優れていることを示す図である。
【図３】従来の背圧を用いた流速計の構成を示す図で、（Ａ）は縦断面図、（Ｂ）は（Ａ）のＹ−Ｙ断面図である。
【図４】従来の背圧を用いた流速計の較正曲線の一例を示す図である。
【符号の説明】
１０流速計
１１測定部
１２支持部
１３全圧取入口
１４背圧取入口
１５圧力センサ
１６温度センサ
１７支持軸
１８軸受
１９回転角度検出器
２０演算部
２１入出力ライン
Ｒ回転軸心
Ｇ回転モーメント中心[0001]
[Industrial applications]
The present invention relates to a velocity meter for measuring the velocity of a fluid.
[0002]
[Prior art]
A pitot tube is used as a measuring instrument for measuring the flow velocity of the fluid. The pitot tube measures the total pressure consisting of the static pressure and the dynamic pressure on the front surface, and measures the static pressure on the side surface to determine the dynamic pressure, from which the flow velocity is determined. However, when the flow velocity is low, the ratio between the total pressure and the static pressure is small and the measurement error is large because the dynamic pressure is small. By the way, a large value is obtained for the ratio between the back pressure on the back of the instrument and the total pressure even if the flow velocity is small. Therefore, a current meter using a back pressure is used.
[0003]
FIG. 3 is a diagram showing an example of a current meter using a total pressure and a back pressure. (A) shows a longitudinal sectional view, and (B) is a YY sectional view of (A). Arrows indicate the flow direction of the fluid. The cross section of the current meter 1 is oval, and the long axis is set in parallel with the flow. A plurality of total pressure inlets 2 are provided on the front side, and a back pressure inlet 3 is provided at the same level at the rear, and an average value of the total pressure (PT) and the back pressure (PB) is obtained. A calibration curve is created from the flow rate obtained by another method, and the flow rate is calculated from the actually measured total pressure and the back pressure using the calibration curve. As a result, it is possible to measure accurately at a relatively low speed.
[0004]
[Problems to be solved by the invention]
The flowmeter using the pitot tube and the total pressure and the back pressure shown in FIG. 3 fixes the flow direction, and sets the flowmeter in accordance with this direction. Therefore, measurement cannot be performed at a position where the flow direction changes. FIG. 4 shows an example of a calibration curve of the anemometer shown in FIG. The vertical axis indicates the total pressure / back pressure ratio, and the horizontal axis indicates the flow rate. The cross section of the anemometer is elliptical, and there are values where the flow characteristics change suddenly, such as the flow around the anemometer changes from laminar to turbulent depending on the Reynolds number (mainly the flow velocity), and a discontinuity occurs in the calibration curve I do. Therefore, it can be used only in a limited range of Reynolds number.
[0005]
The present invention has been made in view of the above-described problems, and has as its object to provide a current meter that can accurately measure a change in the direction of a flow. It is another object of the present invention to provide a current meter that can measure accurately even in a low flow velocity region.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 has a wedge-shaped cross-sectional shape having an isosceles triangle having an intersection of isosceles as a top and an opposite side of the top as a bottom, and measuring a total pressure at a top and a back pressure at a bottom. Measuring part, and a supporting part that rotatably supports the measuring part around an axis perpendicular to the wedge-shaped cross section, and the rotation center of the measuring part is around an axis parallel to the perpendicular axis of the measuring part. Is provided on the top side with respect to the center of the rotational moment, so that the top rotates so as to always face the flow direction of the fluid .
[0007]
According to the second aspect of the present invention, the measuring section is provided with a temperature sensor for measuring the temperature of the fluid.
[0008]
According to the third aspect of the present invention, the support section is provided with a rotation angle detector for detecting a rotation angle of the measurement section.
[0009]
According to the fourth aspect of the present invention, the support unit includes a calculation unit that calculates the flow velocity of the fluid from the total pressure, back pressure, temperature, and calibration data measured by the measurement unit.
[0010]
[Action]
According to the first aspect of the invention, when the top of the wedge faces the flow direction, the ratio or difference between the total pressure at the top of the wedge and the back pressure at the bottom is stable with respect to the Reynolds number. Such a discontinuous point does not occur. Since the back pressure can be measured to a value lower than the side pressure measured by a pitot tube or the like, accurate measurement can be performed even at a low speed by using this back pressure. Further, since the rotation center of the measuring unit is provided on the top side from the center of the rotational moment about the axis parallel to the vertical axis of the measuring unit, the top rotates so as to face the flow. As a result, even if the direction of the flow changes, the measurement unit rotates facing the flow, so that accurate measurement is always possible.
[0011]
According to the second aspect of the present invention, since the temperature sensor for measuring the temperature of the fluid is provided in the measurement unit, the measured value is temperature-corrected, and an accurate flow velocity can be obtained.
[0012]
According to the third aspect of the present invention, the support section is provided with a rotation angle detector for detecting a rotation angle of the measurement section, so that the direction of the flow can be measured.
[0013]
According to the fourth aspect of the present invention, since the support unit includes a calculation unit that calculates the flow velocity of the fluid from the total pressure, back pressure, temperature, and calibration data measured by the measurement unit, the flow velocity value is output as an electric signal. It is an easy-to-use current meter.
[0014]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A and 1B are diagrams showing a configuration of an embodiment, in which FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along line XX of FIG. The current meter 10 includes a measuring unit 11 for measuring the total pressure, the back pressure, and the temperature of the fluid, and a supporting unit 12 that rotatably supports the measuring unit 11. The measuring unit 11 is an isosceles triangle and has a wedge shape with the intersection of the isosceles at the top and the opposite side of the top as the bottom, and the top is rounded and provided with a full pressure inlet 13 for measuring the total pressure of the fluid, A back pressure inlet 14 for measuring back pressure is provided at the bottom on the wedge center line C. Since the wedge shape is an isosceles triangle, it is symmetric with respect to the wedge center line C. Note that a plurality of total pressure inlets 13 and a plurality of back pressure inlets 14 may be provided and communicate with each other as in FIG. The total pressure inlet 13 and the back pressure inlet 14 are each connected to a pressure sensor 15, and the pressure sensor 15 measures the total pressure and the back pressure. A temperature sensor 16 having a detection end near the total pressure inlet 13 is provided, and measures the temperature of the fluid.
[0015]
The measurement unit 11 is rotatably supported by a support shaft 17 provided in a vertical direction in the plan view of FIG. The support shaft 17 is fixed to the measurement unit 11, rotates integrally, and is rotatably supported by a bearing 18 provided on the support unit 12. When the fluid is a liquid, the bearing has a sealed structure. R indicates the rotation center of the support shaft 17. G indicates the center of the rotational moment about an axis parallel to the support shaft 17 of the measuring unit 11. The rotation center R is provided closer to the top of the wedge than the center G of the rotation moment. Accordingly, when the direction indicated by the arrow is the flow direction, the top of the wedge of the measuring unit 11 rotates so as to face the flow direction. As a result, the direction of the flow always coincides with the center line C of the wedge.
[0016]
The support portion 12 is cylindrical and rotatably supports the support shaft 17 by a bearing. A rotation angle detector 19 that detects the rotation angle of the support shaft 17 is provided. By detecting the rotation angle of the measurement unit 11, the direction of the flow with respect to the support unit 12 can be detected. The support shaft 17 is hollow so that the wires of the pressure sensor 15 and the temperature sensor 16 can pass through.
[0017]
The support unit 12 is provided with a calculation unit 20 for calculating the flow velocity of the fluid from the measured values of the total pressure, the back pressure and the temperature and the calibration data. The calibration data is, for example, a table showing the flow rate with respect to the total pressure / back pressure ratio as shown in FIG. The input / output line 21 supplies power to the pressure sensor 15, the temperature sensor 16, the rotation angle detector 19, and the calculation unit 20, and outputs a measured value, a calculated flow rate, and the like.
[0018]
FIG. 2 shows a change in the resistance coefficient with respect to the Reynolds number using the cross-sectional shape as a parameter. When a rectangle, a wedge, an ellipse, and a substantially circle are put in the fluid in the flow direction indicated by the arrow, the drag coefficient of the rectangle and the wedge does not change much even if the flow velocity (the Reynolds number corresponds to the flow velocity) changes. On the other hand, the resistance coefficient of an ellipse and a substantially circle changes greatly after a certain flow velocity. A large change in the coefficient of resistance indicates that the nature of the flow has changed, for example, from laminar to turbulent. When the nature of the flow changes, the calibration curve becomes discontinuous as shown in FIG. The rectangle has a small change in the resistance coefficient, but has a large resistance coefficient. The wedge has a small change in the resistance coefficient with respect to the change in the flow velocity, and has a small resistance coefficient. For this reason, no discontinuity point occurs in the calibration curve, and it can be seen that the cross-sectional shape of the measuring unit is suitable for measuring the flow velocity in a wide range.
[0019]
【The invention's effect】
As is clear from the above description, the present invention calculates the flow rate by measuring the total pressure at the top of the wedge and measuring the back pressure at the bottom of the wedge. Since the back pressure is lower than the side pressure measured with a pitot tube or the like, it is possible to measure accurately at low speeds. Also, since the flow of the fluid to the wedge does not change even if the flow velocity changes, the calibration curve used to calculate the flow velocity from the total pressure and back pressure does not have a discontinuity point, and a wide range of flow velocity is measured. can do. Further, by disposing the rotation center of the measurement unit on the top side of the wedge from the rotation moment center of the measurement unit, the top always faces the fluid flow direction. Thus, even when the apparatus is installed in a place where the direction of the flow is unknown, correct measurement can always be performed, and the direction of the flow can be measured.
[Brief description of the drawings]
1A and 1B are diagrams showing a configuration of an embodiment of the present invention, wherein FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along line XX of FIG.
FIG. 2 is a diagram showing that a wedge shape is excellent as a cross-sectional shape of a measurement unit.
3A and 3B are diagrams showing a configuration of a conventional anemometer using a back pressure, wherein FIG. 3A is a longitudinal sectional view, and FIG. 3B is a sectional view taken along line YY of FIG.
FIG. 4 is a diagram showing an example of a calibration curve of a conventional anemometer using a back pressure.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Current meter 11 Measurement part 12 Support part 13 Full pressure inlet 14 Back pressure inlet 15 Pressure sensor 16 Temperature sensor 17 Support shaft 18 Bearing 19 Rotation angle detector 20 Operation part 21 Input / output line R Rotation axis G Rotation moment center

Claims

A measuring section for measuring the total pressure at the top and measuring the back pressure at the bottom with a wedge-shaped cross-section having an isosceles triangle with the intersection of the isosceles as the top and the opposite side of the top as the bottom, and a wedge-shaped cross-section And a support portion rotatably supported around an axis perpendicular to the axis, wherein the rotation center of the measurement section is provided on the top side with respect to the center of the rotational moment about an axis parallel to the vertical axis of the measurement section. The anemometer characterized in that the top rotates so as to always face the fluid flow direction .

The current meter according to claim 1, wherein the measuring unit is provided with a temperature sensor for measuring a temperature of the fluid.

The current meter according to claim 1, wherein a rotation angle detector that detects a rotation angle of the measurement unit is provided on the support unit.

The flow meter according to claim 2, wherein the support unit includes a calculation unit that calculates a fluid flow velocity from the total pressure, back pressure, temperature, and calibration data measured by the measurement unit.