JPH11190647A - Flowmeter utilizing thermal flow sensor and gas meter utilizing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an accurate detection of a flow amount value without depending on the directions of flow passage and flow by selecting an offset value, linealizing data, conversion counting inherent in a measured gas according to the directions of flow passage and flow, and compensating the detection output of flow sensor according to the selected compensation value. SOLUTION: Temperature sensor lines Ru, Rd of a flow sensor mounted in a flow passage 10 constitutes a bridge circuit 22. The circuit 22 is connected to a power source 21, then variation in the distribution of temperature depending on the amount of flow generating in the flow passage 10 is generated as a voltage value, and a sensor detection output F which is A-D converted 23 is supplied to a microcomputer 20. The microcomputer 20 performs signal processing, so that the convereted flow amount value and the calculated flow amount value are displayed on an instant flow amount display 25 and/or a calculation flow amount display 24. The direction of flow passage or the like is input to the microcomputer 20, which selects an optimum zero (0) point compensation value, linealized compensation data and the conversion counting value inherent in fluid in order to give an accurate flow value to a flow display 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow meter using a thermal type flow sensor, and more particularly, to selecting an optimum correction value in accordance with a mounting direction of a flow sensor and a flowing direction of a fluid to obtain a more accurate flow rate. The present invention relates to a flow meter capable of measuring a flow rate and a gas meter using the same.

[0002]

2. Description of the Related Art A thermal type flow sensor has attracted attention as a sensor capable of detecting a flow rate of a fluid, particularly a mass flow rate of a gas such as a gas. In a general thermal type flow sensor, a temperature sensor is arranged on an upstream side and a downstream side of a hot wire, and a temperature distribution of radiant heat from the hot wire that changes according to a flow rate of a fluid is detected by a pair of temperature sensors. . In recent years, a micro flow sensor provided with a heating wire and a temperature sensor on a semiconductor chip has been developed, and is becoming widespread in semiconductor manufacturing apparatuses, gas meters, and the like.

FIG. 1 is a diagram for explaining the outline of such a thermal type flow sensor. Channel 10 through which gas to be measured flows
Inside, a heat wire Rh and a temperature sensor wire R arranged upstream thereof.
u and a flow sensor composed of a temperature sensor line Rd arranged on the downstream side. Then, by applying a constant voltage V0 to the heating wire Rh, radiant heat is generated from the heating wire Rh, and a temperature distribution is generated on the upstream side and the downstream side. If the fluid flows in the flow path 10 in the direction of the arrow in the figure, the temperature distribution moves downstream accordingly.
The amount of movement of this temperature distribution downstream depends on the mass flow rate of the fluid.

FIG. 2 is a diagram showing a movement of a temperature distribution in the above-mentioned thermal type flow sensor. The horizontal axis shows the position of the flow path,
The vertical axis shows the temperature. The solid line shows the temperature distribution when the flow rate Q is zero. In this temperature distribution, the position H of the hot wire has the highest temperature, and the temperature decreases at positions U (upstream) and D (downstream) on both sides. The temperatures at the two temperature sensors Ru and Rd are substantially equal. The broken line is the temperature distribution when the flow rate Q is a predetermined flow rate Qs. As described above, the temperature distribution moves downstream, and the temperature at the downstream temperature sensor Rd becomes higher than the temperature at the upstream temperature sensor Ru. The flow rate is detected according to the degree of the difference between the temperatures of the two temperature sensors.

As shown in FIG. 1, the temperature sensor lines Ru and Rd of the flow sensor constitute a Wheatstone bridge circuit together with the resistors R1 and R2. The resistance of the temperature sensor lines Ru and Rd increases when the temperature is high, and the resistance decreases when the temperature is low. Therefore, utilizing such characteristics, a temperature difference is detected by a voltage difference between the nodes ns and nr of the bridge circuit. Reference numeral 14 denotes a differential amplifier for detecting a voltage difference between the two nodes ns and nr, and its output is an analog flow sensor detection output 16.

[0006]

However, in the above-mentioned thermal type flow sensor, the detection output when the flow rate is zero may differ depending on the mounting direction of the flow sensor.
That is, as described above, in the thermal flow sensor, radiant heat is generated from the middle heat wire. As shown in FIG. 1, when the flow sensor is installed so that the heat wire Rh and the temperature sensor wires Ru and Rd are in the horizontal direction, the radiant heat from the heat wire Rh is substantially equal to the left and right when the flow rate is zero. To spread.
As a result, as shown by the solid line in FIG. 2, the temperature distribution becomes symmetrical in the upstream and downstream directions, the resistance values on the temperature sensor lines Ru and Rd become equal, and the sensor detection output in the state of zero flow becomes zero.

However, when the flow sensor is placed in a flow path in which the flow direction of the fluid is vertical, the temperature sensor lines Ru and Rd are arranged above and below the heating wire Rh. In this case, it has been found that convection occurs in the gas or fluid in the flow channel due to the radiant heat from the hot wire Rh, and the temperature above the hot wire Rh tends to increase. Therefore, when the flow sensor is attached to the vertical flow path, the sensor output has a constant offset value even when the flow rate is zero.

[0008] The above problem of offset due to convection needs to be treated as a positive offset value or a negative offset value depending on the direction in which the fluid flows.

As a second problem, the detection output from the thermal flow sensor generally does not have a linear characteristic with respect to the flow rate. Therefore, usually, linearization calculation is performed on the sensor detection output using linearization curve data indicating the relationship between the detection output and the flow rate obtained in the experiment. In that case, strictly speaking, the convective characteristics of the fluid are different depending on the viscosity and the molecular weight of the fluid. As a result, it is expected that the above-mentioned linearization curve also differs depending on the convection characteristics.

As a third problem, although the thermal type flow sensor can detect the mass flow rate, it is necessary to correct it according to the composition of the fluid. For example, the composition of the gas differs depending on the gas type in the gas meter. Due to the different composition of the fluid, the convection characteristics also differ, and such corrections also
It is expected that it will differ depending on the convection characteristics described above.

An object of the present invention is to provide a flow meter using a thermal flow sensor capable of detecting an accurate flow rate value independent of the direction of a flow path and the direction of a flow.

Further, another object of the present invention is to automatically detect the direction of the flow path and the direction of the flow from the detection value of the flow sensor, and to obtain an accurate flow rate value independent of the direction of the flow path and the direction of the flow. It is an object of the present invention to provide a flow meter using a thermal type flow sensor capable of detecting the flow rate and a gas meter for integrating the flow value.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention firstly provides an offset value, linearization data, a conversion specific to a metered gas according to the direction of a flow path and the direction of a flow. Select the coefficient, etc., and according to the selected correction value,
It is characterized in that the detection output of the flow sensor is corrected to obtain an accurate flow value.

Further, secondly, the present invention automatically detects the direction of the flow path from the offset value of the sensor detection output value when the flow rate is zero. Also, the direction of the flow is automatically detected based on a change in the sensor detection output value even at a predetermined flow rate.

[0015] Furthermore, the present invention, third, the direction of the flow path,
Automatic detection is performed using a signal from a direction detection means attached to the flow sensor.

According to the above invention, according to the detection result of the direction of the flow path, particularly the horizontal (horizontal) direction or the vertical (vertical) direction,
It is possible to select an optimal offset value, linearization data, a conversion coefficient specific to the measured gas, and the like. Therefore, more accurate flow rate detection can be performed. Further, since the direction of the flow path and the direction of the flow can be automatically detected using the sensor detection output, it is possible to obtain the optimum correction data without bothering the human hand. The direction of the flow path and the direction of the flow can be generally referred to as the direction of the flow of the fluid. Therefore, the flow direction of the fluid includes the angle of the flow path (vertical or horizontal) and the direction in which the fluid flows (top to bottom, bottom to top, left to right, right to left). Is included.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. However, the technical scope of the present invention is not limited to the embodiment.

FIG. 3 is a view for explaining a case where the flow sensor is placed horizontally when the flow path is in the horizontal direction. FIG.
(1) shows a state in which the heating wire Rh and the temperature sensor wires Ru and Rd are arranged in the horizontal flow path 10, as in FIG. In the case of such a horizontal installation, a pair of temperature sensor lines Ru,
Convection has almost no effect on Rd. Accordingly, as shown in FIG. 3 (2), the temperature distribution is symmetrical from the position H of the hot wire Rh to the upstream side and the downstream side when the flow rate Q = 0. When the fluid flows from left to right, FIG.
The temperature distribution moves as indicated by the broken line in (2). Conversely, when the fluid flows from right to left, the temperature distribution moves as shown by the dashed line in FIG.

Therefore, when the flow rate Q = 0, the detection output is also zero, and when the fluid flows from left to right, FIG.
It is necessary to adopt a correction curve in the first quadrant as the linearize curve of (3). On the other hand, when the fluid flows from right to left, it is necessary to adopt the correction curve of the third quadrant as the linearize curve in FIG.

Further, depending on the type of gas, the linearize curve needs to be slightly corrected as shown by the arrow. Therefore, if necessary, a coefficient specific to the metered fluid is selected depending on the gas type and the flow direction of the fluid.

FIG. 4 is a view for explaining a case where the flow sensor is placed vertically when the flow path is vertical. FIG.
(1) shows a state in which the heat wire Rh and the temperature sensor wires Ru and Rd are arranged in the vertical flow path 10 unlike FIG. The temperature sensor wire Ru is arranged above the heating wire Rh, and the temperature sensor wire Rd is arranged below the heating wire Rh.

As shown in FIG. 4A, when a flow sensor is attached to a vertical flow path, radiant heat generated from the hot wire Rh causes convection. Therefore, in the state of the flow rate Q = 0, the temperature distribution shifts upward as shown by the solid line in FIG. As a result, the sensor detection output F0 detected when the flow rate Q = 0 is shifted to the negative side. That is, the offset value has a certain magnitude.

In addition, the convection affects not only the offset value but also the linearize curve shown in FIG. That is, the linearize curve in which the flow path is in the horizontal direction does not simply shift by the offset value F0, but the linearize curve differs due to convection as shown by the arrow in the figure. Further, it is expected that the optimum value of the conversion coefficient unique to each fluid such as the gas type differs depending on the convection characteristics.

Accordingly, if necessary, a linearization curve may be selected depending on the direction of the flow of the fluid, and a coefficient specific to the measurement fluid may be selected depending on the gas type and the flow direction of the fluid. Will be

FIG. 5 is a circuit configuration diagram of a flow meter and a gas meter according to an embodiment of the present invention. As described with reference to FIG. 1, the temperature sensor lines Ru and Rd of the flow sensor mounted in the flow path 10 constitute the bridge circuit 22. The bridge circuit 22 is connected to the power supply 21 and the flow path 1
A change in the temperature distribution depending on the flow rate occurring within 0 is generated as a voltage value and supplied to the AD conversion circuit 23. Therefore,
The digitized sensor detection output F is supplied to a microcomputer (flow rate conversion unit) 20 that converts the detection signal F into a flow rate, which will be described later. Microcomputer 2
In the case of 0, the signal processing described later is performed, and the flow rate value obtained by integrating the converted flow value by the instantaneous flow display 25 and / or the integration circuit 211 is displayed on the integrated flow display 24.

The microcomputer 20 includes, for example,
A manual switch 25 for inputting a data signal in the direction of the flow path or the flow direction to which the flow sensor is attached is connected. As the manual switch 25, for example, a hardware switch such as a jumper switch, a dip switch, and a rotary switch is used. Further, the microcomputer 20 may be connected to an automatic detection switch 26 described later. By using a switch mounted on the flow sensor and capable of automatically detecting the mounting direction, the mounting direction can be automatically given to the microcomputer 20 instead of manually.

The microcomputer 20 includes a zero-point correction calculator 202 for correcting an offset value with respect to the sensor detection output F, a linearization calculator 205 for correcting non-linearity of the flow sensor, and a gas type. Calculation unit 20 for converting the flow rate according to a conversion coefficient specific to the survey fluid
8 is provided. These calculation units 202, 205, 208
As a result, the sensor detection output F is converted into a flow rate value, and an accurate flow rate value is given to the flow rate display 24.

The zero point correction calculation unit 202 is, for example, a RAM
Using the data in the zero-point correction value memory 203 storing the zero-point correction value, the correction calculation of the zero point is performed. The correction data in the zero point correction memory 203 may be selected from a zero point correction value table 204 stored in advance depending on the direction of the flow path and the direction of the flow,
The zero point correction value 211 obtained from the sensor detection output F detected when the flow rate is zero may be adopted and stored. The zero point correction table 204 may be stored in, for example, a built-in ROM, or may be stored in an EEPROM that is a rewritable nonvolatile memory.

The linearization calculation unit 205 performs a linearization calculation of a detection output by using data of a linearization correction data memory 206 which stores linearization correction data such as a RAM. This linearization correction data is specifically shown in FIG.
This is data of the linearization curve shown in (3) or (3) of FIG. 4, and is selected from the linearization correction data table 207 stored in advance according to the direction of the flow path and the direction of the flow.

The flow rate conversion operation unit 208 performs a flow rate conversion operation using a conversion coefficient corresponding to a gas type and the like, using data in a conversion coefficient memory 209 storing a conversion coefficient such as a RAM. This conversion coefficient is stored in advance in a conversion coefficient table 210 according to the direction of the flow path and the direction of the flow.
Is selected from

Each of the above tables 204, 207, 210
Are selected by the selection signal 212 from the flow path / flow direction detection unit 201, and are stored in the corresponding memories 203, 206, and 209. The flow path / flow direction detection unit 201 receives a detection output F from the flow sensor and detects the direction of the flow path and the flow direction from the value of the detection output F. Alternatively, it is detected by a signal from the manual switch 25 described above. Alternatively, the direction of the flow path is detected based on a signal from the automatic detection switch 26 described above. Then, according to the detected direction of the flow path and the direction of the flow, a selection signal 212 for selecting the optimum correction data of each table is supplied to each table.

FIG. 6 is a flow chart of the flow measurement. The flow chart shows a method of automatic detection by the flow path / flow direction detection unit 201 described above. First, the detection output F of the flow sensor in a state where the flow rate is zero is obtained (S10). At this time, the sensor detection output F should be zero in an ideal state, but has a constant offset amount due to characteristics unique to the flow sensor. Further, when the flow path is in the vertical direction, the zero value of the flow sensor has an extremely large offset value in addition to the offset value due to the above characteristics. Therefore, when the offset value of the detection output F in the zero flow state is a large value exceeding a certain threshold value (S1)
In 1), it is detected that the flow path is in the vertical direction and the flow sensor is in the vertical position (S12). On the other hand, when the offset value of the detection output F is small even when the flow rate is zero (S
11), it is detected that the flow path is in the horizontal direction and the flow sensor is in the horizontal state (S13).

Next, a fluid is caused to flow through the flow path 10 so as to maintain a constant flow rate. The detection output F of the flow sensor at that time is obtained (S14). Then, if the change of the detection output F is positive (S15), as shown in FIGS. 3 (1) and 4 (1),
It is detected that the fluid is flowing from the position U to the direction D (S16). Conversely, if the change in the detection output F is negative (S
15) It is detected that the fluid is flowing from the position D in the direction of U (S17).

From the direction of the flow path 10 and the direction of the flow detected as a result of the above-described flow sensor output detection, an optimum zero point correction value, linearization data, and a conversion coefficient are selected from respective tables. Is performed (S18, S19). Here, since the sensor detection output at zero flow rate has been acquired, (1) the zero point correction data closest to the detected offset value is selected from the table 204, or
(2) Any method of storing the detected offset value itself as the zero point correction data 211 in the zero point correction memory 203 can be used. In the latter method (2), it is possible to cope with the change of the zero point due to the aging of the flow sensor.

Then, according to each of the correction data selected as described above, the instantaneous flow rate value and the instantaneous flow rate value are calculated by the zero point correction calculation unit 202, the linearization calculation unit 205 and the flow rate conversion calculation unit 208 from the sensor detection output F detected thereafter. An integrated flow value is obtained (S20).

FIG. 7 is a diagram showing an example of an automatic flow direction detection switch. In this example, a flow rate display unit 32 rotatable in the direction of an arrow 34 is attached to a pipe 30 to which a heat wire and a temperature sensor wire of a flow sensor are attached. FIG.
(1) shows the position of the flow rate display unit 32 with respect to the pipe 30 when the flow path direction is vertical and the gas flow is from top to bottom. When the flow sensor is attached, the operator rotates the flow display unit 32 so that the flow is always in the horizontal direction and the gas flow is from the top to the bottom of the display unit. At that time, by using the output of the encoder provided in the flow rate display unit 32, the flow path / flow direction detection unit 201 in the microcomputer 20
It is possible to provide the detection signal.

In FIG. 7B, the operator rotates and installs the flow rate display unit 32 so that the flow direction is horizontal and the flow of gas is from the left side to the right side of the display unit 32.

FIG. 8 is a diagram showing an example of another automatic flow direction detection switch. In this example, a direction detection switch 33 that detects whether the flow path is vertical or horizontal is attached to the display unit 32 of the pipe to which the flow sensor is attached, for example, on the side wall. This direction detection switch 33 is
For example, a small magnet ball 36 is inserted into a hollow sphere so as to be freely movable in the hollow sphere. Then, the two reed switches 34 and 35 are attached at positions in the horizontal direction and the downward direction.

The direction detecting switch 33 moves the magnet 36 toward the reed switch B when the pipe 30 forming the flow path is installed in the horizontal direction. On the other hand, when the pipe 30 is installed in the vertical direction, the magnet 36 moves to the reed switch A side. The signal from each reed switch is
As a detection signal from the automatic detection switch 26 shown in FIG.
Flow path / flow direction detector 2 in microcomputer 20
01 is supplied. In this example, the flow direction cannot be detected only by detecting the angle of the flow path. Accordingly, the flow direction is detected according to steps S15 to S17 in the flowchart of FIG.

The above reed switches 34 and 35 are
In either case, if the installation direction is always horizontal or vertical, either direction can be detected.

Further, the present invention is not limited to the direction detection switch using the above-described reed switch. For example, a switch having a mechanism for detecting a terrestrial magnetism angle by a terrestrial magnetism sensor can be used. In addition to the reed switch, an angle detection switch of a type provided with a switch that is turned on by the weight of the weight depending on the position of the internal weight can be used.

Further, when the above embodiment is used as a flow meter in a gas meter, the direction of the flow path and the direction of the flow can be controlled by a communication means used for automatic meter reading and automatic shutoff. It can also be given to a computer.

Further, when used as a flow meter of a gas meter, it is obliged by the gas metering method that when the flow path is in a vertical direction, the flow of the gas is from top to bottom. When the flow path is in the horizontal direction, the flow of the gas is obligatory from left to right. Therefore, if there is such a legal restriction, there is no need to detect the direction of the flow described above.

[0044]

As described above, according to the present invention, in a flow meter using a thermal type flow sensor, optimum zero point correction values, linearization correction data, Since the conversion coefficient value unique to the fluid is selected, it is possible to eliminate a measurement error due to a convection phenomenon of the generated fluid depending on the installation direction.

Further, since the direction of the flow path and the direction of the flow of the fluid can be automatically detected from the sensor detection output, the correction data can be accurately selected without bothering the operator. be able to.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a thermal type flow sensor.

FIG. 2 is a diagram showing movement of a temperature distribution in a thermal flow sensor.

FIG. 3 is a diagram illustrating a case where the flow sensor is placed horizontally.

FIG. 4 is a diagram illustrating a case where the flow sensor is placed vertically.

FIG. 5 is a circuit configuration diagram of a flow meter according to the embodiment of the present invention.

FIG. 6 is a flowchart of a flow rate measurement.

FIG. 7 is a diagram showing an example of an automatic flow direction detection switch.

FIG. 8 is a diagram illustrating an example of an automatic flow direction detection switch.

[Explanation of symbols]

 Rh Heat wire Ru, Rd Temperature sensor 20 Flow rate converter

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Ken Tashiro 36-3 Sunakubo, Kawagoe-shi, Saitama (72) Inventor Junzo Kimura 2-12-19 Shibuya, Shibuya-ku, Tokyo Inside Yamatake Honeywell Co., Ltd. (72 Inventor Yasuharu Oishi 2-12-19 Shibuya, Shibuya-ku, Tokyo Yamatake Honeywell Co., Ltd. (72) Inventor Hiroyuki Inagaki 2-12-19 Shibuya, Shibuya-ku, Tokyo Yamatake Honeywell Co., Ltd. (72) Inventor Seo Masami 2-12-19 Shibuya, Shibuya-ku, Tokyo Yamatake Honeywell Co., Ltd. (72) Inventor Junichi Iseya 2-12-19 Shibuya, Shibuya-ku, Tokyo Yamatake Honeywell Co., Ltd.

Claims (10)

[Claims] 1. A flow meter using a thermal flow sensor having a heat wire and a temperature sensor provided apart from each other in a flow direction of a fluid, wherein an offset value at a zero flow rate according to the direction of the flow of the fluid. A flow rate conversion unit that selects or stores the flow rate and performs zero point correction of the detection output from the flow sensor according to the selected offset value. 2. A flow meter using a thermal flow sensor having a heat wire and a temperature sensor provided separately in a flow direction of a fluid, wherein detection from the flow sensor is performed in accordance with a flow direction of the fluid. Select the linearized data to be converted from output to flow rate,
A flowmeter, comprising: a flow rate conversion unit for obtaining a flow rate from a detection output of the flow sensor according to the selected linearized data. 3. A flow meter using a thermal type flow sensor having a heat wire and a temperature sensor provided separately in a flow direction of a fluid, wherein a conversion factor specific to the flow rate is set according to a direction of a flow of the fluid. A flow meter, comprising: a flow rate conversion unit that selects data and calculates a flow rate from a detection output of the flow sensor according to the selected conversion coefficient data. 4. The flowmeter according to claim 1, wherein the flow direction of the fluid is a vertical direction or a horizontal direction. 5. The flowmeter according to claim 1, wherein the data on the direction of the flow of the fluid is provided to the flow rate conversion unit by a manual switch. 6. The method according to claim 1, wherein the flow direction of the fluid is detected by the flow rate conversion unit from the flow sensor detection output when the flow rate is zero. Flowmeter. 7. The method according to claim 1, wherein the flow direction of the fluid is such that the flow rate conversion unit changes the output of the flow sensor detection between a state of zero flow and a state of a predetermined flow rate. A flowmeter characterized by detecting from the direction of. 8. The flow direction of the fluid according to claim 1, wherein a flow direction of the fluid is set in accordance with the flow direction of a flow rate display unit rotatably provided in the flow meter. A flow meter characterized by being detected from a rotation angle. 9. The flow sensor according to claim 1, wherein said flow sensor is mounted on a pipe forming a flow path to which said flow sensor is mounted, and detects a horizontal / vertical direction according to a direction of the flow path. A flowmeter comprising an angle detecting means, wherein direction data is supplied from the angle detecting means to the flow rate conversion section. 10. The gas meter according to claim 1, wherein the determined flow rate is integrated.