JP2965464B2 - Flowmeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow meter for measuring a flow rate of a fluid such as a gas.

[0002]

2. Description of the Related Art As a flow meter used in a gas meter or the like, a flow meter using a hot wire anemometer is known. The hot-wire anemometer obtains the flow velocity by utilizing the fact that the cooling rate of the hot-wire arranged in the pipe becomes a function of the flow velocity of the fluid flowing in the pipe, and in the flow meter using this hot-wire anemometer, The flow rate is calculated from the flow velocity and is displayed.

FIG. 5 shows an example of a configuration of a flow meter using a conventional hot-wire anemometer. This flow meter is connected to piping 1
For example, a flow rate sensor 102 is provided in the center of the device 01. The flow rate sensor 102 has a heating wire 103, and the heating wire 103 has a resistor 10 connected in series.
4, a DC power supply 105 is connected. An arithmetic circuit 106 for calculating the flow rate is provided at both ends of the resistor 104.
Is connected to the arithmetic circuit 106, and a display unit 107 for displaying the flow rate is connected.

Here, the supply voltage of the power supply 105 is V ₀ , the resistance of the heating wire 103 is r ₀ , the resistance of the resistor 104 is R ₀ , and the current flowing through the heating wire 103 and the resistor 104 is i.
_{Assuming 0} , there is a relationship of the following equation (1).

[0005]

I ₀ = V ₀ / (R ₀ + r ₀ ) (1)

Here, if r ₀ >> R ₀ , equation (1) is approximated as equation (2) below.

[0007]

I ₀ = V ₀ / r ₀ (2)

Since the resistance value r ₀ of the heating wire 103 changes with the flow velocity, when the voltage V ₀ is constant, the current i ₀ also changes with the flow velocity according to the equation (2). Therefore, the flow rate Q ₀ corresponding to the flow velocity is a function of the current i ₀ and can be expressed as in the following equation (3).

[0009]

## EQU3 ## Q ₀ = K ₀ × (i ₀ −i ₀₀ ) (3)

In the equation (3), K ₀ is a coefficient corresponding to a pipe or the like, and i ₀₀ is a current flowing through the heating wire 103 and the resistor 104 when the flow rate Q ₀ = 0.

The current i ₀ in equation (3) is
When 4 of the ends of the voltage is v _0, Motomari as _{i 0 = v 0 / R 0} , the arithmetic circuit 106 in FIG. 5 calculates the flow rate Q _0, based on the equation (3). The calculated flow rate Q
₀ is displayed on the display unit 107.

[0012]

However, the piping 1
In the flow velocity 01, the flow velocity distribution on the same cross section varies depending on the difference in the pipe shape, the presence of a bent portion, a branch portion, or the like, or the magnitude of the flow rate. Further, in the pipe 101, the range of the measurement place where the change in the flow velocity is proportional to the change in the flow rate is narrow. Therefore, with a conventional flow meter in which the flow velocity sensor 102 is disposed at one location in the pipe 101, only the flow velocity at one location in the pipe 101 can be determined, and thus the flow rate can be accurately determined in a wide flow rate measurement range. There was a problem that it was not possible.

In order to cope with this, a flow rate sensor is arranged at each of a plurality of positions in a pipe, and an average value of flow rates at a plurality of positions in the pipe is calculated based on output signals of the plurality of flow rate sensors. Can be considered. However, in this case, if the flow velocity is calculated based on the output signals of the plurality of flow velocity sensors, and the average value is further calculated, the configuration of the flow meter becomes complicated.

The present invention has been made in view of the above problems, and has as its object to provide a flow meter which has a simple structure and can accurately measure the flow rate regardless of the flow velocity distribution in the piping. To provide.

[0015]

The flowmeters according to the present invention are each heated by an electric current and respond to a temperature.
Has a heating element whose resistance value changes, and in the piping,
Positions in the direction perpendicular to the longitudinal direction of
Flow sensors arranged at a plurality of positions
Speed sensor heating element connected in parallel to a common constant voltage power supply
And the sum of the currents flowing through each of these heating elements
A flow velocity detection circuit that outputs a corresponding value, and the flow velocity detection circuit
Calculates the flow rate of the fluid flowing in the pipe based on the output of the road
And a flow rate calculating means.

In this flow meter, each flow rate sensor is
The temperature and resistance of the heating element change, and as a result,
The total current flowing through the heating element changes. Flow velocity detection circuit
The value corresponding to the sum of this current is distributed by each flow sensor.
The parameter that depends on the average value of the flow velocity at the set position
Output as data. Based on the output from this flow rate detection circuit
The flow rate of the fluid flowing through the piping
The quantity is calculated.

[0017]

[0018]

[0019]

[0020]

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a schematic cross-sectional structure of a flow meter according to a first embodiment of the present invention, and FIG. 2 shows a cross-sectional structure in the direction of arrows AA in FIG. The flow meter according to the present embodiment includes a cylindrical sensor unit 13 disposed at a predetermined position in a pipe 11 through which a fluid a such as a gas passes so as to be orthogonal to the flow direction of the fluid a. Sensor unit 1
Four fluid passing holes 13 ₁ along the flow direction of the fluid a is 3, 13 _2, 13 _3, 13 ₄ are provided. In the sensor unit 13, these fluid passage holes 13 _{1 to} 13 _{1
4 A} plurality of, for example, four flow velocity sensors 1 at positions facing each
2 _1, 12 _2, 12 _3, 12 ₄ are disposed. That is, in the flow meter of the present embodiment, in the pipe 11, a plurality of positions in the direction orthogonal to the longitudinal direction of the pipe 11 are different from each other, particularly, a plurality of positions different from each other on the same cross section in the pipe 11. , four flow sensors 12 ₁ to 12
₄ are arranged in a vertical line.

FIG. 3 is a circuit diagram showing a circuit configuration of the flow meter according to this embodiment. Hereinafter, for generalization of the description, the number of flow velocity sensors is assumed to be N. As shown in FIG. 3, in the flow meter of the present embodiment, each of the flow rate sensors 12 ₁ ,
12 _2, 12 _3, ..., 12 _N is heated by the current, hot wire 15 ₁ as a heat generating element whose resistance value in response to temperature changes, 15 _2, 15 _3, ..., a 15 _N I have. Here, each of the heating wires 15 ₁ , 15 ₂ , 15 ₃ ,.
_Let the resistance values of _{N be} r ₁ , r ₂ , r ₃ ,..., R _N.

Further, the flow meter of the present embodiment has
5 _1, 15 _2, 15 _3, ..., and a flow rate detection circuit 20 connected in parallel to 15 _N against a common power supply 21.
Power supply 21 is a stabilized power supply for generating a constant voltage V _1. Further, the flow rate detection circuit 20, one end each of the heat ray 15 _first power source 21, 15 _2, 15 _3, ..., and a resistor 22 interposed between one end of the 15 _N. The output terminal 30a at both ends of the resistor 22, from 30b, the flow rate sensors 12 _1, 12 _2, 12 _3, ..., as a parameter 12 _N depends on the average value of the flow velocity in the disposed position, the hot wire 15 _1, 15 _2, 15 _3, ..., and outputs a value corresponding to the sum I of the current flowing through the 15 _N. That is, assuming that the resistance value of the resistor 22 is R, the voltage between the output terminals 30a and 30b at both ends of the resistor 22 is IR
Therefore, this voltage becomes a value corresponding to the sum I of the current.

The output terminals 30a and 30b are connected to a calculation circuit 23 as flow calculation means for calculating the flow rate of the fluid flowing through the pipe 11 based on the output of the flow velocity detection circuit 20. A display unit 24 for displaying the flow rate is connected to the arithmetic circuit 23.

Next, the operation of the flow meter of this embodiment will be described.

Each flow sensor 12 _n (n = 1, 2, 3,
..., the hot wire 15 _n of N), a constant voltage V from the power supply 21
₁ is applied. Here, the current flowing through each heat ray 15 _n and i _n, When r _n >> R, a relationship of the following equation (4).

[0028]

## EQU4 ## i _n = V ₁ / r _n (4)

[0029] Since changes with the resistance value r _n is the flow rate of the hot wire 15 _n, the current i _n also varies with flow rate. Accordingly, the flow rate Q _n corresponding to the flow velocity at the position where the flow rate sensor 12 _n are provided is a function of current i _n, can be expressed as the following equation (5).

[0030]

[Equation 5] _{Q n = K 1 × (i} n -i n0) ... (5)

In the equation (5), i _n0 is the flow rate Q _n
The current flowing through each heating wire 15 _n when = 0. Also,
K ₁ is a coefficient corresponding to the piping, the hot wire 15 _n is K _1> 0 in the case of metal, in the case of the semiconductor becomes K ₁ <0.

Accordingly, the flow rate Q corresponding to the average value of the flow velocity at the position where each flow velocity sensor 12 _n is provided is expressed by the following equation (6).

[0033]

[6] Q = (1 / N) × ΣQ n = (1 / N) × K 1 × Σ (i n -i n0) = (1 / N) × K 1 × (I-I 0) ... ( 6)

Note that nQ _n is Q ₁ , Q ₂ , Q ₃ ,.
_Represents the sum of _N , and Σ (i _n −i _n0 ) is i ₁ −i ₁₀ , i ₂
−i ₂₀ , i ₃ −i ₃₀ ,..., I _N −i _N0 . Further, I ₀ is the value of each heating wire 15 ₁ , 1 when the flow rate Q = 0.
5 _2, 15 _3, ..., it is the sum of the current flowing through the 15 _N.

The current I in the equation (6) is obtained from the voltage between the output terminals 20a and 20b at both ends of the resistor 22, as described above. Therefore, the arithmetic circuit 23 in FIG. 3 calculates the flow rate Q based on the equation (6). Accordingly, the flow rate Q corresponding to the average value of the flow velocity at the position where each flow velocity sensor 12 _n is provided is obtained by the arithmetic circuit 23. The flow rate Q obtained by the arithmetic circuit 23 is displayed on the display unit 24.

As described above, according to the present embodiment, the plurality of flow rate sensors 1 are provided in the pipe 11 at a plurality of different positions in the direction orthogonal to the longitudinal direction of the pipe 11.
The 2 _n arranged, by using the flow rate sensor 12 _n, since to obtain the flow rate Q corresponding to the average value of the flow velocity at the position where the flow rate sensor 12 _n is arranged, changed by a difference or the like of the pipe-shaped Irrespective of the flow velocity distribution in the pipe 11, the flow rate can be accurately measured, and as a result, the flow rate can be accurately measured over a wide range from a small flow rate to a large flow rate.

Further, in this embodiment, the flow rate detection circuit 20, in connected in parallel heat rays 15 _n of each flow sensor 12 _n to a common power supply 21, the flow sensor 12 _n is disposed position A value corresponding to the sum I of the current flowing through each heating wire 15 _n is output as a parameter depending on the average value of the flow velocity, and the flow rate Q of the fluid flowing through the pipe 11 is calculated based on the output of the flow velocity detection circuit 20. Like that. Therefore, a circuit for calculating each flow velocity based on the output signals of the plurality of flow velocity sensors and further calculating an average value thereof is not required, and the configuration of the flow meter can be simplified.

FIG. 4 is a circuit diagram showing a circuit configuration of a flow meter according to a second embodiment of the present invention. In the flow meter of the present embodiment,
Instead of the flow velocity detection circuit 20 in the first embodiment, a flow velocity detection circuit 30 for connecting each heating wire 15 _n in series to a common power supply 31 is provided. The power supply 31 has a constant current I
_It is a constant current power supply that supplies ₀ . This flow velocity detection circuit 30
Is the supply voltage V of the power supply 31 which is a value corresponding to the sum of the resistance values of the heating wires 15 _n as a parameter depending on the average value of the flow speed at the position where each flow sensor 12 _n is provided.
₂ is output from the output terminals 30a and 30b. Further, the flow meter of the present embodiment includes an arithmetic circuit 33 connected to the output terminals 30a and 30b of the flow velocity detecting circuit 30 instead of the arithmetic circuit 33 of the first embodiment. The display unit 24 is connected to the arithmetic circuit 33.

Next, the operation of the flow meter of this embodiment will be described.

A constant current I ₀ is supplied from a power supply 31 to the heating wire 15 _n of each flow velocity sensor 12 _n . Since changes with the resistance value r _n is the flow rate of the hot wire 15 _n, the sum? R _n of the resistance value of each heating wire 15 _n also varies with flow rate, the sum? R _n of the resistance value of each flow sensor 12 _n This is a parameter that depends on the average value of the flow velocity at the arranged position.

The flow rate Q corresponding to the average value of the flow velocity at the position where each flow velocity sensor 12 _n is provided is expressed by the following equation (7).

[0042]

[Equation 7] _{Q = K 2 × (1 /} N) × Σ (r n -r n0) = K 2 × (1 / N) × (V 2 -V 20) / I 0 ... (7)

Note that r _n0 is the value of each heating wire 1 when the flow rate Q = 0.
5 _n resistance value, V ₂₀ is output terminal 30 when flow rate Q = 0
a and 30b. K ₂ is a coefficient corresponding to a pipe or the like. When each heating wire 15 _n is a metal, K ₂ <
0, and in the case of a semiconductor, K ₂ > 0.

The voltage V ₂ in the equation (7) is obtained as a voltage between the output terminals 30a and 30b as described above. Therefore, the arithmetic circuit 33 in FIG. 4 calculates the flow rate Q based on the equation (7). Therefore, the flow rate Q corresponding to the average value of the flow velocity at the position where each flow velocity sensor 12 _n is provided is calculated by the arithmetic circuit 33. The flow rate Q obtained by the arithmetic circuit 33 is displayed on the display unit 24.

Other structures, operations and effects are the same as those of the first embodiment.

The present invention can be applied not only to the measurement of the flow rate of a gas such as a gas, but also to a flow meter for measuring the flow rate of a liquid.

[0047]

As described above, according to the flow meter of the present invention , a plurality of flow rate sensors are arranged at a plurality of positions in the pipe, the positions being different from each other in a direction orthogonal to the longitudinal direction of the pipe. The heating elements of each flow rate sensor are connected in parallel to a common constant voltage power supply , and
A flow velocity detection circuit that outputs a value corresponding to the total current flowing is provided, and the flow rate of the fluid flowing through the pipe is calculated based on the output of the flow velocity detection circuit. There is an effect that the flow rate can be measured accurately regardless of the flow velocity distribution.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a flow meter according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG. 1;

FIG. 3 is a circuit diagram illustrating a circuit configuration of the flow meter according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram illustrating a circuit configuration of a flow meter according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a configuration of an example of a flow meter using a conventional hot-wire anemometer.

[Explanation of symbols]

11 piping 12 _{1 to} 12 _N flow sensor 15 ₁ to 15 _N heat wire 20 flow detection circuit 21 power supply 22 resistor 23 arithmetic circuit 24 display

Claims (1)

(57) [Claims] 1. A plurality of positions each having a heating element which is heated by an electric current and whose resistance value changes in accordance with a temperature, wherein positions in a direction orthogonal to a longitudinal direction of the pipe are different from each other. Multiple flow rate sensors and the heating element of each flow rate sensor are connected in parallel to a common constant voltage power supply .
Connected to each other , and as a parameter that depends on the average value of the flow velocity at the position where each flow velocity sensor is disposed ,
A flow rate detection circuit that outputs a value corresponding to the total current flowing through the body; and a flow rate calculation means that calculates a flow rate of the fluid flowing through the pipe based on an output of the flow rate detection circuit. Flowmeter.