JP3998295B2 - Mass flow meter - Google Patents

Description

ここで、ｆ（Ｑｍ）は質量流量Ｑｍの関数を意味する。
【００４４】
コイル(8)の電圧Ｅｓから流体(1)の質量流量Ｑｍを測定する場合は、先述のように電圧Ｅ_Sが周囲温度Ｔａにより影響を受けないようにΔＴをＴａの関数として制御するが、そのΔＴとＴａとの関係を求める。
【００４５】
コイル(8)の抵抗値をＲｓとすると、
Ｐ＝Ｅｓ²／Ｒｓ
となり、抵抗の温度係数をα、基準抵抗をＲｓoとすると、
Ｒｓ＝Ｒｓo（１＋αＴｓ）
であるので、上記の式(1)は
Ｅｓ²＝｛Ｒｓo（１＋αＴｓ）（Ｔｓ−Ｔａ）｝Θ・ｆ（Ｑｍ） （式２）
と書き換えることができる。
【００４６】
次に、（式２）からＴａの影響を除去して流量を算出できる条件を求める。周囲温度Ｔａの基準温度をＴａoとし（Ｔａoは適宜定めればよく、例えば２５℃等と定めることができる）、そのときのコイル(8)の温度をＴｓoとすると、
（１＋αＴｓ）（Ｔｓ−Ｔａ）＝（１＋αＴｓ）ΔＴ＝Ｃ
＝（１＋αＴｓo）（Ｔｓo−Ｔａo） （式３）
となり（Ｃは定数）、ΔＴ＝Ｔｓ−Ｔａ、すなわちＴｓ＝ΔＴ＋Ｔａであるので、
（１＋αΔＴ＋αΔＴａ）ΔＴ−Ｃ＝０
これを整理すると、α・ΔＴ²＋（１＋αＴａ）ΔＴ−Ｃ＝０ （式４）
となる。
【００４７】
（式４）の解を求め、２α・Ｃ／（１＋αＴａ）＜１のときの近似式は、
ΔＴ≒Ｃ／（１＋αＴａ）
となり（式３）の関係から、
ΔＴ≒（Ｔｓo−Ｔａo）（１＋αＴｓo）（１−αＴａ） （式５）
となる。
【００４８】
したがって、（式５）に従ってΔＴをＴａの関数として変化させることによって、出力電圧Ｅｓは、周囲温度Ｔａの影響を受けることなく極めて安定な値が得られる。
【００４９】
尚、本発明は実用上分流を必要としていた従来の質量流量計の弊害を解消し、大きな流量を正確に計測可能とすることを目的とするので、基本的に分流は設けない。しかしながら、特に流量が多い場合には分流を設けることによって対応することができる。この場合、分流を設けたことによる悪影響は生じるが、従来のものに比べて分流素子を構成する細管の数を大幅に少なくすることができ（例えば数本以下）、コストが低減できるほか、分流による悪影響も格段に少なく抑えることができる。
【００５０】
又、本実施例では計測後の流体(1)を再度ボディ(3)内を通して流体出口(7)に導いているが、ボディ(3)の熱容量は十分に大きいため、加熱された計測後の流体の温度によりボディ(3)の流体入口(2)の温度が上昇してしまうようなことはない。必要であれば、計測後の流体(1)を再度ボディ(3)内を通すことなく質量流量計外に導くような構成としてもよい。
【００５１】
［比較試験］
周囲温度Ｔａがコイル(8)の電圧Ｅｓに与える影響を確認するために、ΔＴを一定とした場合と、ΔＴを（式５）にしたがって周囲温度Ｔａに対応して変化させた場合について、電圧Ｅｓの偏差を調べた。
【００５２】
図４はΔＴを１０℃に固定した場合を示した図であり、(A)は周囲温度ＴａとΔＴとの関係を示し、(B)は電圧Ｅｓの２５℃の値に対する偏差を示している。図から電圧Ｅｓは周囲温度Ｔａの変化とともに変化していることがわかる。
【００５３】
図５はΔＴを周囲温度Ｔａに対応して変化させた場合を示した図であり、(A)は周囲温度ＴａとΔＴとの関係を示し、(B)は電圧Ｅｓの２５℃の値に対する偏差を示している。図から電圧Ｅｓは周囲温度Ｔａが変化してもほとんど変化していない。したがって、コイル(8)の電圧Ｅｓに基づいて流量を算出する場合には、ΔＴを周囲温度Ｔａの関数として制御することにより、流量の測定がより正確になることがわかる。
【００５４】
［実施例２］
図６は本実施例の構成の概要を示した図である。基本構成は図１に示した実施例１と同様であるが、加熱・感熱コイルが２本(81),(82)並列に接続されている点が異なる。この場合でも実施例１と同様の効果が得られる。又、同様にして加熱・感熱コイルを３本以上並列に接続してもよい。
【００５５】
【発明の効果】
以上述べたように、本発明によりバイパスの存在に基づく弊害を解消し、大きな流量でも計測でき、周囲温度の影響による誤差を生じにくく、しかも安全性が高く安価な質量流量計を提供することができた。
【図面の簡単な説明】
【図１】実施例１の構成の概要を示した図。
【図２】実施例の温度分布を示した図。
【図３】電子回路の構成の概要を示した図。
【図４】ΔＴ一定の場合の電圧Ｅｓの偏差を示した図。
【図５】ΔＴを周囲温度Ｔａに対応して変化させた場合の電圧Ｅｓの偏差を示した図。
【図６】実施例２の構成の概要を示した図。
【図７】従来の分流式の質量流量計の構成の概要を示した図。
【符号の説明】
(1) 流体
(2) 流体入口
(3) ボディ（伝熱ブロック）
(4) 導管
(5) フランジ
(6) マスフローセンサ管
(7) 流体出口
(8) 加熱・感熱コイル
(9) 周囲温度センサ
(10) 埋設穴
(11) 熱伝導性樹脂
(12) シール材
(13) 蓋体
(14) 断熱材
(15) 電子回路基板
(16) 周囲温度変換回路
(17) コイル温度検出回路
(18) コイル加熱回路
(19) 流量演算回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mass flow meter, and more particularly, to a mass flow meter capable of measuring a large flow rate without a shunt (bypass).
[0002]
[Prior art]
A mass flow meter (mass flow meter) is used to measure a mass flow rate of a gas or a liquid in a manufacturing process of a semiconductor such as a VLSI or a manufacturing process in various industries.
[0003]
The basic principle of the thermal mass flowmeter is that the fluid (gas or liquid) to be measured is flowed into the conduit, and the fluid in the conduit is heated directly or indirectly with a heater, and the difference between the ambient temperature and the coil temperature upstream. And detecting the difference between the ambient temperature and the coil temperature downstream (or detecting the difference between the amount of heat deprived upstream and the amount of heat deprived upstream) to determine the flow rate. ing.
[0004]
However, with this method, the amount of change in the amount of heat that the fluid takes from the coil decreases rapidly with an increase in flow rate, so when the flow rate of the fluid to be measured is large, the difference between upstream and downstream decreases, and the accurate mass It becomes difficult to measure the flow rate. Therefore, it can be applied only to the measurement of minute flow rate.
[0005]
Therefore, in recent years, a partial flow (bypass) is provided to divide a part of the fluid flowing through the conduit at a predetermined rate, measure the mass flow rate of the minute fluid passing through the mass flow sensor tube, and calculate based on the measurement result. In addition, a shunt-type mass flow meter that calculates the mass flow rate of the entire amount by performing correction and conversion is widely used.
[0006]
FIG. 7 is a diagram showing an outline of the configuration of a shunt-type mass flow meter. In order to make the flow rate of the fluid passing through the mass flow sensor pipe (23) and the fluid passing through the branch flow (20) a predetermined ratio, the branch flow (20) is provided with a bypass element (22). The bypass element (22) generally has a structure in which several to several thousand thin tubes (21) having the same or similar diameter as the mass flow sensor tube (23) are bundled.
[0007]
Since a current is passed through the thermal element, it also serves as a heater, so two thermal elements (24) and (25), one upstream and one downstream, are used. Today, this is the basic and standard configuration of mass flow meters.
[0008]
However, the presence of the bypass element tends to cause a flow rate error due to a difference in size and structure between the mass flow sensor tube and the bypass element, and is easily influenced by a flow rate value due to a difference in ambient temperature or fluid temperature.
[0009]
In addition, there is a problem that gas adsorption to the bypass element and the accompanying residual gas cause contamination of the semiconductor manufacturing process, and that the apparatus causes a solid difference in flow rate value due to assembly errors and dimensional errors in bypass manufacturing. In addition, the structure is complicated and the cost is increased.
[0010]
There are other negative effects of the bypass element.
Since the sensitivity of each fluid with respect to the mass flow sensor has a different value, it is most desirable to actually use various fluids when manufacturing the mass flow meter in order to maintain accuracy and eliminate solid differences.
[0011]
However, if an actual gas or the like is allowed to flow, a part of the product will remain inside and lead to contamination of the semiconductor manufacturing process at the sales destination. Further, since actual gases are highly reactive and many are toxic, it is problematic in terms of safety to always store them during production. Furthermore, it causes a significant cost increase.
[0012]
Therefore, it is common to calibrate products here using nitrogen gas instead of actual gas. Therefore, prior to calibration, the sensitivity ratio of the mass flow sensor between various gases and nitrogen gas is measured and managed as numerical data. This numerical value is called a conversion coefficient (conversion factor: hereinafter abbreviated as “CF”). In manufacturing, the nitrogen gas is flowed and the flow rate is calibrated using the CF for each gas. In the inspection stage after calibration, whether or not the flow rate is accurately calibrated is measured. At this time, nitrogen gas is also used.
[0013]
After such a configuration and inspection, it is delivered to the customer as a passing product and installed, but at the stage of acceptance inspection and device start-up by the customer, the measurement flow rate is not accurate or there is a difference in individual device May be found. This is because nitrogen gas is used for conversion with CF and calibration is performed, and no actual gas is used. In other words, the CF is not accurate, is different between models and device solids, and is caused by the difference in flow rate.
[0014]
Further, the flow rate output from the mass flow sensor is generally affected by changes in ambient temperature. Therefore, a temperature compensation circuit that electrically corrects the temperature effect is often provided in the electric circuit. To compensate for temperature, the product is set in a thermostatic chamber, the temperature is changed while flowing calibration nitrogen gas, and calibration is performed using a mass flow meter as a reference.
[0015]
At that time, the temperature characteristics differ depending on the flow rate due to differences in the shape, material, structure, dimensions, etc. of the bypass element and the mass flow sensor. Therefore, an accurate flow rate calibration value cannot be obtained simply by correcting using the CF value as data. Therefore, the flow rate error at the delivery destination may be a problem.
[0016]
Since such a problem is caused by providing a shunt provided with a bypass element, it is desirable not to provide a shunt if possible. As a method that does not use a diversion, there is a calorimeter mass flow meter with a uniformly heated conduit. In this method, an alternating current is directly applied to a metal conduit to heat the conduit uniformly.
[0017]
This method does not cause the above-mentioned inconvenience due to the presence of the shunt current, but it is rarely adopted because there is a risk of ignition due to sparks due to the current flowing directly through the tube, especially focusing on safety. The possibility of being adopted in the semiconductor field is extremely low.
[0018]
And if the flow rate is large, the temperature change of the fluid due to heating becomes minute and difficult to detect, so the conventional fundamental problem that the flow rate that can be measured is small has not been solved.
[0019]
[Problems to be solved by the invention]
Therefore, in order to eliminate the flow measurement error due to the presence of the bypass, it is basically a structure that does not have a bypass, it can measure even a large flow rate, hardly causes an error due to the influence of the ambient temperature, and is safe and inexpensive. A total is required.
[0020]
[Means for Solving the Problems]
In the mass flow meter according to claim 1 of the present invention, one coil (8) serving both for heating and temperature detection is wound around the mass flow sensor tube (6), and before the fluid to be measured (1) is heated. In the mass flowmeter that calculates the flow rate from the temperature difference between the ambient temperature and the coil temperature substantially the same as the temperature, and the power or voltage supplied to the coil (8), the temperature difference changes as a function of the ambient temperature, and the coil The coil temperature is controlled so that the voltage supplied to is not affected by the ambient temperature .
[0021]
In the mass flow meter according to claim 2, one coil (8) serving both for heating and temperature detection is wound around the mass flow sensor tube (6), and is approximately equal to the temperature before heating of the fluid to be measured (1). A temperature sensor (9) for detecting the same ambient temperature, an ambient temperature detection circuit (16) connected to the temperature sensor (9), a coil temperature detection circuit (17) for detecting the coil temperature, and a coil temperature The coil heating circuit (18) to be controlled and the flow rate calculation circuit (19) have a flow rate based on the temperature difference between the ambient temperature and the coil temperature and the power or voltage supplied to the coil (8). In the mass flowmeter that calculates the temperature, the temperature difference changes as a function of the ambient temperature, and the coil temperature is controlled so that the voltage supplied to the coil is not affected by the ambient temperature .
[0022]
In the mass flow meter according to claim 3 of the present invention, a plurality of coils (81), (82) connected in parallel for both heating and temperature detection are wound around the mass flow sensor tube (6). In the mass flowmeter that calculates the flow rate from the temperature difference between the ambient temperature and the coil temperature that is substantially the same as the temperature before heating the measurement fluid (1), and the power or voltage supplied to the coil (8), the temperature difference is: The coil temperature is controlled so as to change as a function of the ambient temperature and the voltage supplied to the coil is not affected by the ambient temperature .
[0023]
In the mass flow meter of claim 4, a plurality of coils (81), (82) connected in parallel for both heating and temperature detection are wound around the mass flow sensor tube (6), and the fluid to be measured ( A temperature sensor (9) that detects the ambient temperature substantially the same as the temperature before heating in 1), an ambient temperature detection circuit (16) connected to the temperature sensor (9), and a coil temperature detection that detects the coil temperature A circuit (17), a coil heating circuit (18) for controlling the coil temperature, and a flow rate calculation circuit (19). The flow rate calculation circuit includes a temperature difference between the ambient temperature and the coil temperature, and a coil (8). In mass flowmeters that calculate flow rate based on supplied power or voltage, coil temperature is controlled so that the temperature difference changes as a function of ambient temperature and the voltage supplied to the coil is not affected by ambient temperature It is characterized by being.
[0024]
The mass flow meter according to claim 5 is the mass flow meter according to any one of claims 1 to 4, wherein the temperature sensor (9) for detecting the ambient temperature is substantially the same as the temperature of the fluid to be measured (1) before heating. It is attached to the heat transfer block (3) which becomes temperature.
[0027]
The mass flow meter according to claim 6 is the mass flow meter according to any one of claims 1 to 5, wherein a relationship between a temperature difference between the coil temperature and the ambient temperature and the ambient temperature is ΔT = (Tso−Tao) ( 1 + αTso) (1-αTa)
It is controlled to become. In the above equation, ΔT is the temperature difference between the coil temperature and the ambient temperature, Ta is the ambient temperature, Tao is the reference ambient temperature, Tso is the temperature of the heating / thermal coil when Tao, and α is the temperature of the coil resistance. Is the temperature coefficient.
[0028]
A mass flow meter according to claim 7 is the mass flow meter according to any one of claims 1 to 6, wherein the mass flow meter does not have a shunt.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to preferred embodiments.
[Example 1]
FIG. 1 is a diagram showing a configuration of a main part of the present embodiment.
[0030]
(1) is a fluid to be measured, and flows through the mass flow sensor pipe (6) from the fluid inlet (2) toward the fluid outlet (7). A heating / heat-sensitive coil (hereinafter simply referred to as “coil”) (8) is uniformly wound around the mass flow sensor tube (6) over a predetermined length.
[0031]
(3) is a body composed of a heat transfer block, (4) is a conduit provided in the body (3), and is a passage for guiding the fluid (1) to the mass flow sensor pipe (6). (5) is a flange, and (13) is a lid. (12) is a sealing material arranged at the contact portion between the body (3) and the flange (5), and (14) is arranged around the mass flow sensor pipe (6) in the space inside the flange (5). It is a heat insulating material.
[0032]
(9) is an ambient temperature sensor, which is embedded in an embedded hole (10) provided in the body (3), and is filled with a heat conductive resin (11). The temperature (ambient temperature) Ta of the body (3) detected by the ambient temperature sensor (9) is high in the thermal conductivity of the body (3) and the thermally conductive resin (11). It can be approximated to be approximately equal to the temperature of the fluid (1) passing through 4). The ambient temperature sensor (9) is not necessarily embedded in the body (3), and may be attached to the body (3), for example.
[0033]
(15) is an electronic circuit board. The configuration of the electronic circuit of the electronic circuit board (15) is shown in FIG. (16) is an ambient temperature conversion circuit which is connected to the ambient temperature sensor (9) and transmits data detected at the fluid inlet (2) of the fluid (1) to a coil heating circuit (18) described later.
[0034]
(17) is a coil temperature detection circuit, which detects the voltage Es and current Is of the coil (8), calculates and calculates the resistance value Rs and coil temperature Ts of the coil (8), and supplies it to the coil heating circuit (18). To transmit.
[0035]
(18) is a coil heating circuit, which calculates a temperature difference ΔT between the coil temperature Ts and the ambient temperature Ta, and controls and supplies the voltage Es of the coil (8) so that the value becomes a desired value.
[0036]
(19) is a flow rate calculation circuit, which performs processing such as linearization processing and flow rate configuration based on the detected coil voltage Es and current Is to convert it into a signal proportional to the mass flow rate of the fluid.
[0037]
Since there is no split flow, the entire amount of the fluid (1) flows into the mass flow sensor pipe (6) and is heated by the heating / heat sensitive coil (8).
The mass flow rate Qm of the fluid (1), the measured value of the power P or the voltage E _S is supplied to the coil (8) is calculated based on the temperature difference [Delta] T.
[0038]
In the case of calculating on the basis of the voltage E _S supplied to the coil (8), the resistance value Rs of the coil (8) is changed by the influence of the ambient temperature Ta, the voltage E _S influenced by the ambient temperature Ta become. Therefore, it is desirable that the voltage E _S to prevent the influence of the ambient temperature Ta.
[0039]
FIG. 2 is a diagram showing a temperature distribution of a fluid for flow rate measurement. If the coil temperature Ts is Ts1 when the ambient temperature Ta is Ta1, Ts1 is controlled so that ΔT1 = Ts1−Ta1 when the temperature difference ΔT between the temperature Ts of the coil (8) and the ambient temperature Ta is ΔT1. To do. If the coil temperature is Ts2 when the ambient temperature Ta reaches Ta2, Ts2 is controlled so that ΔT2 = Ts2−Ta2. As described above, the temperature difference ΔT between the temperature Ts of the coil (8) and the ambient temperature Ta is not constant, but may be changed according to the change of the ambient temperature Ta. That is, by controlling the ΔT as a function of Ta, it can be the voltage E _S to be unaffected by the ambient temperature Ta. Conditions for this will be described later.
[0040]
The mass flowmeter of the present invention is not based on the comparison between upstream and downstream as in the prior art, but is calculated based on the measured value at one place, so that it can sufficiently measure even when the flow rate is large.
[0041]
The coil (8) part of the mass flow sensor tube (6) is approximately an isothermal wall, and the change in temperature of the fluid (1) in the mass flow sensor tube (6) is approximately the laminar boundary on the isothermal wall. It takes the form of a temperature distribution of the fluid in the bed.
[0042]
While the fluid (1) passes through the mass flow sensor tube (6), the amount of heat absorbed from the heating / heat sensitive coil (8) is equal to the power consumption P of the coil (8), and the axial direction x of the mass flow sensor tube (6) The difference ΔT (x) between the temperature Ts (x) of the coil (8) and the boundary layer temperature (approximate to the ambient temperature) Ta (x) of the coil (8) in each minute portion dx of the fluid (1) and the coil ( It is the distance integral value of the coil length of the value Θ (x) · ΔT (x) multiplied by the thermal conductivity Θ between (8) and expressed by the following (Equation 1).
[0043]
[Expression 1]

Here, f (Qm) means a function of the mass flow rate Qm.
[0044]
When measuring the mass flow rate Qm of the fluid (1) from the voltage Es of the coil (8) is a voltage E _S as previously described to control the ΔT so as not to be affected by the ambient temperature Ta as a function of Ta, The relationship between ΔT and Ta is obtained.
[0045]
When the resistance value of the coil (8) is Rs,
P = Es ² / Rs
When the temperature coefficient of resistance is α and the reference resistance is Rso,
Rs = Rso (1 + αTs)
Therefore, the above equation (1) can be expressed as Es ² = {Rso (1 + αTs) (Ts−Ta)} Θ · f (Qm) (equation 2)
Can be rewritten.
[0046]
Next, a condition for removing the influence of Ta from (Equation 2) and calculating the flow rate is obtained. If the reference temperature of the ambient temperature Ta is Tao (Tao may be determined as appropriate, for example, 25 ° C. or the like), and the temperature of the coil (8) at that time is Tso,
(1 + αTs) (Ts−Ta) = (1 + αTs) ΔT = C
= (1 + αTso) (Tso−Tao) (Formula 3)
(C is a constant) and ΔT = Ts−Ta, that is, Ts = ΔT + Ta.
(1 + αΔT + αΔTa) ΔT−C = 0
To summarize this, α · ΔT ² + (1 + αTa) ΔT−C = 0 (Formula 4)
It becomes.
[0047]
Obtaining the solution of (Expression 4), the approximate expression when 2α · C / (1 + αTa) <1 is
ΔT ≒ C / (1 + αTa)
From the relationship of (Equation 3),
ΔT≈ (Tso−Tao) (1 + αTso) (1−αTa) (Formula 5)
It becomes.
[0048]
Therefore, by changing ΔT as a function of Ta according to (Equation 5), the output voltage Es can be obtained as an extremely stable value without being affected by the ambient temperature Ta.
[0049]
The present invention aims to eliminate the disadvantages of the conventional mass flow meter that required a diversion in practice and to enable a large flow rate to be measured accurately, so that no diversion is basically provided. However, in particular, when the flow rate is large, it can be dealt with by providing a diversion. In this case, there is an adverse effect due to the provision of the diversion, but the number of narrow tubes constituting the diversion element can be significantly reduced compared to the conventional one (for example, several or less), the cost can be reduced, and the diversion The adverse effects due to can be significantly reduced.
[0050]
Further, in this embodiment, the measured fluid (1) is again guided to the fluid outlet (7) through the body (3), but since the heat capacity of the body (3) is sufficiently large, The temperature of the fluid inlet (2) of the body (3) does not increase due to the temperature of the fluid. If necessary, the configuration may be such that the measured fluid (1) is guided out of the mass flowmeter without passing through the body (3) again.
[0051]
[Comparison test]
In order to confirm the influence of the ambient temperature Ta on the voltage Es of the coil (8), voltage ΔT is constant and voltage ΔT is changed according to the ambient temperature Ta according to (Equation 5). The deviation of Es was examined.
[0052]
FIG. 4 is a diagram showing a case where ΔT is fixed at 10 ° C., (A) shows the relationship between the ambient temperature Ta and ΔT, and (B) shows the deviation of the voltage Es from the value of 25 ° C. . It can be seen from the figure that the voltage Es changes with changes in the ambient temperature Ta.
[0053]
FIG. 5 is a diagram showing a case where ΔT is changed corresponding to the ambient temperature Ta, (A) shows the relationship between the ambient temperature Ta and ΔT, and (B) shows the voltage Es with respect to a value of 25 ° C. The deviation is shown. From the figure, the voltage Es hardly changes even when the ambient temperature Ta changes. Therefore, when the flow rate is calculated based on the voltage Es of the coil (8), it is understood that the flow rate can be measured more accurately by controlling ΔT as a function of the ambient temperature Ta.
[0054]
[Example 2]
FIG. 6 is a diagram showing an outline of the configuration of this embodiment. The basic configuration is the same as that of the first embodiment shown in FIG. 1 except that two heating and thermal coils (81) and (82) are connected in parallel. Even in this case, the same effect as in the first embodiment can be obtained. Similarly, three or more heating / thermal coils may be connected in parallel.
[0055]
【The invention's effect】
As described above, the present invention eliminates the adverse effects due to the presence of the bypass, and can provide a mass flow meter that can be measured even at a large flow rate, is less likely to cause an error due to the influence of the ambient temperature, and is highly safe and inexpensive. did it.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of a configuration of a first embodiment.
FIG. 2 is a diagram showing a temperature distribution of an example.
FIG. 3 is a diagram showing an outline of a configuration of an electronic circuit.
FIG. 4 is a diagram showing a deviation of voltage Es when ΔT is constant.
FIG. 5 is a diagram showing a deviation of voltage Es when ΔT is changed corresponding to ambient temperature Ta.
6 is a diagram showing an outline of the configuration of Embodiment 2. FIG.
FIG. 7 is a diagram showing an outline of the configuration of a conventional shunt-type mass flow meter.
[Explanation of symbols]
(1) Fluid
(2) Fluid inlet
(3) Body (heat transfer block)
(4) Conduit
(5) Flange
(6) Mass flow sensor tube
(7) Fluid outlet
(8) Heating / thermal coil
(9) Ambient temperature sensor
(10) Buried hole
(11) Thermally conductive resin
(12) Seal material
(13) Lid
(14) Insulation
(15) Electronic circuit board
(16) Ambient temperature conversion circuit
(17) Coil temperature detection circuit
(18) Coil heating circuit
(19) Flow rate calculation circuit

Claims (7)

A coil for both heating and temperature detection is wound around the mass flow sensor tube. The temperature difference between the ambient temperature and the coil temperature is approximately the same as the temperature before heating of the fluid to be measured, and the power supplied to the coil. Or in a mass flow meter that calculates flow rate from voltage,
The mass flowmeter, wherein the temperature difference changes as a function of the ambient temperature, and the coil temperature is controlled so that the voltage supplied to the coil is not affected by the ambient temperature . A coil for both heating and temperature detection is wound around the mass flow sensor tube, and a temperature sensor for detecting an ambient temperature substantially the same as the temperature of the fluid to be measured before heating is connected to the temperature sensor. An ambient temperature detection circuit; a coil temperature detection circuit for detecting a coil temperature; a coil heating circuit for controlling the coil temperature; and a flow rate calculation circuit, wherein the flow rate calculation circuit includes a temperature difference between the ambient temperature and the coil temperature; In a mass flow meter that calculates the flow rate based on the power or voltage supplied to the coil,
The mass flowmeter, wherein the temperature difference changes as a function of the ambient temperature, and the coil temperature is controlled so that the voltage supplied to the coil is not affected by the ambient temperature . Around the mass flow sensor tube, a plurality of coils connected in parallel for both heating and temperature detection are wound. The temperature difference between the ambient temperature and the coil temperature, which is substantially the same as the temperature before heating the fluid to be measured, and the coil In the mass flow meter that calculates the flow rate from the power or voltage supplied to the
The mass flowmeter, wherein the temperature difference changes as a function of the ambient temperature, and the coil temperature is controlled so that the voltage supplied to the coil is not affected by the ambient temperature . Around the mass flow sensor tube, a plurality of coils connected in parallel for both heating and temperature detection are wound, and a temperature sensor for detecting an ambient temperature substantially the same as the temperature before heating of the fluid to be measured, and the temperature sensor An ambient temperature detection circuit connected to the coil, a coil temperature detection circuit for detecting the coil temperature, a coil heating circuit for controlling the coil temperature, and a flow rate calculation circuit, wherein the flow rate calculation circuit calculates the ambient temperature and the coil temperature. In the mass flowmeter that calculates the flow rate based on the temperature difference and the power or voltage supplied to the coil,
The mass flowmeter, wherein the temperature difference changes as a function of the ambient temperature, and the coil temperature is controlled so that the voltage supplied to the coil is not affected by the ambient temperature .   5. The mass flow rate according to claim 1, wherein the temperature sensor that detects the ambient temperature is attached to a heat transfer block that has substantially the same temperature as the temperature of the fluid to be measured before heating. Total. 6. The relationship between the temperature difference and the ambient temperature is controlled so that ΔT = (Tso−Tao) (1 + αTso) (1−αTa). Mass flow meter.
In the above equation, ΔT is the temperature difference between the coil temperature and the ambient temperature, Ta is the ambient temperature, Tao is the reference ambient temperature, Tso is the temperature of the heating / thermal coil when Tao, α is the coil Is the temperature coefficient of the temperature of the resistance.   The mass flow meter according to any one of claims 1 to 6, wherein the mass flow meter does not have a diverted flow.

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