JPH05107092A - Thermal flowmeter - Google Patents

Abstract

PURPOSE:To obtain the flowmeter capable of easily achieving the enlargement of a measurement flow area. CONSTITUTION:A flow control valve 13 is provided on a bypath 6. A ratio of the flow allowed to flow in a sensor tube 1 to the other flow allowed to flow in the bypath 6, namely, a separation ratio can easily be regulated by regulating a degree of the opening of the flow control valve 13. The enlargement of a measurement flow area can be easily achieved without being accompanied by the exchange and the like of parts. Furthermore, its share in addition to the number of the parts can be lessened by contriving the enlargement of the measurement flow area without being accompanied by the exchange and the like of the parts and workability is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow meter for detecting a temperature difference generated in a fluid and measuring the flow rate of the fluid.

[0002]

2. Description of the Related Art As an example of a conventional thermal type flow meter, there is a split type thermal type flow meter shown in FIG. In the figure, reference numeral 1 denotes a sensor tube through which a fluid passes, and the sensor tube 1 is made of a thin metal material such as stainless steel or a resin material such as fluororesin. A coil-shaped heater 2 is provided in the middle of the sensor tube 1.
Are fitted in close contact with each other. A constant voltage circuit 3 is connected to the heater 2, and a constant voltage is applied to the heater 2 to cause the heater 2 to generate heat, and the heat generated by the heater 2 heats the fluid with a constant amount of heat P.

Upstream and downstream temperature sensors 4 and 5 for detecting the temperature of the fluid are provided on the upstream and downstream portions of the heater 2 of the sensor tube 1, respectively. Each of the upstream and downstream temperature sensors 4 and 5 is composed of a small thermistor, a thin film platinum resistance temperature detector, or a thin wire made of metal such as platinum having a large temperature coefficient, and has excellent responsiveness. It has become.

A bypass pipe 6 is provided in the sensor pipe 1 so as to bypass the upstream and downstream temperature sensors 4, 5. A flow dividing element 7 having an orifice is fitted in the bypass pipe 6, and the flow dividing element 7 is replaced with a flow dividing element 7 having an orifice of a different size.
A ratio (hereinafter, referred to as a diversion ratio) α between the flow rate Q ₁ flowing through the bypass pipe 6 and the flow rate Q ₂ flowing through the bypass pipe 6 can be changed.

A temperature difference detection circuit 8 is provided so as to be connected to the upstream and downstream temperature sensors 4 and 5, and an arithmetic circuit 10 is connected to the temperature difference detection circuit 8 via an amplifier circuit 9. The temperature difference detection circuit 8 includes upstream and downstream temperature sensors 4, 5
Of each of the upstream and downstream detection temperatures _Ta ,
The detected temperature difference ΔT (ΔT = T _b −T _a ) is obtained by inputting T _b , and this detected temperature difference ΔT is output to the arithmetic circuit 10.

The arithmetic circuit 10 is configured to detect the temperature difference ΔT and the heater 2
The flow rate Q ₁ passing through the sensor tube 1 is calculated based on the constant heating amount P supplied to the fluid from
The total flow rate Q of the fluid is calculated from ₁ and the flow dividing ratio α.

In this thermal type flow meter, the temperature is detected by the upstream and downstream temperature sensors 4 and 5 in a state where a constant amount of heat P is supplied per hour from the heating element to the fluid. The flow rate Q ₁ of the fluid passing through the sensor tube 1 is measured based on the detected temperature ΔT and the heating amount P, and the total flow rate Q of the fluid is obtained from the flow rate Q ₁ and the diversion ratio α. Further, in this thermal type flow meter, the flow dividing element 7 is replaced to set an appropriate flow dividing ratio according to the flow rate change range of the fluid,
The measurement flow rate range is wide.

[0008]

By the way, in the above-mentioned thermal type flow meter, since the flow dividing element is provided in the pipe, it is inconvenient that the flow dividing ratio cannot be changed and the measurement flow range can be expanded easily. It was a thing.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thermal type flow meter capable of easily achieving an expansion of a measurement flow rate range.

[0010]

In order to achieve the above object, the present invention has a heating element attached to a pipe through which a fluid is passed, and the upstream side and the downstream side of the heating element are connected to the upstream side and the downstream side of the heating element, respectively. In a thermal type flow meter in which a temperature detecting means is provided and a bypass pipe 6 is provided in the pipe so as to bypass both temperature detecting means, a flow control valve is provided in at least one of the pipe and the bypass pipe 6. Is characterized by.

[0011]

According to this structure, the ratio of the flow rate of the sensor tube to the flow rate of the bypass tube, that is, the flow rate of the sensor tube by adjusting the opening degree of the flow rate control valve provided in at least one of the tube and the bypass tube, that is, The diversion ratio can be easily adjusted.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A thermal type flow meter according to a first embodiment of the present invention will be described below with reference to FIGS. The same members as those shown in FIG. 6 are designated by the same reference numerals and the description thereof will be omitted.

In the figure, an electromagnetic flow control valve 13 having a needle-shaped valve element 11 and a solenoid 12 for driving the valve element 11 is provided in the middle of the bypass pipe 6 instead of the flow dividing element 7 of FIG. Are provided. An arithmetic circuit 14 is provided in connection with the temperature difference detection circuit 8, a control circuit 15 is provided in connection with the flow rate control valve 13, and a diversion ratio setting circuit 16 is provided in connection with the control circuit 15 and the arithmetic circuit 14. Has been.

The opening of the flow control valve 13 is proportional to the flow rate of the fluid flowing through the bypass pipe 6 as shown in FIG. 2, and the sensor can be adjusted by adjusting the opening of the flow control valve 13. A ratio (hereinafter referred to as a diversion ratio) α between the flow rate Q ₁ flowing through the pipe 1 and the flow rate Q ₂ flowing through the bypass pipe 6 can be changed.

The diversion ratio setting circuit 16 is connected to an input means (not shown) that is manually operated. By inputting an instruction signal corresponding to the diversion ratio α from this input means, the flow control valve 13 will be described later. To generate a shunt ratio setting signal a, which is output to the arithmetic circuit 14 and the control circuit 15.

The control circuit 15 receives the shunt ratio setting signal a to generate a control signal b corresponding to the shunt ratio setting signal a, and outputs the control signal b to the solenoid 12 to turn the valve element 11 on. Flow control valve driven to correspond to control signal b
It is designed to set the opening of 13.

The arithmetic circuit 14 inputs the detected temperature difference ΔT based on the relationship of the following expression (1) between the detected temperature difference ΔT and the constant heating amount P supplied to the fluid from the heater 2. Equation (1) is calculated to obtain the flow rate Q ₁ passing through the sensor tube 1. ΔT = k · [P / (ρ · _CP · Q)] (1) ρ: density, Q: heating amount, _CP : specific heat, k: coefficient,

The arithmetic circuit 14 further calculates the equation (2) because the flow rate Q ₁ , the flow rate Q ₂ flowing through the bypass pipe 6, the total flow rate Q and the diversion ratio α are related by the following equation (2). The total flow rate Q flowing into the thermal flow meter is calculated.

Q = Q ₁ + Q ₂ = Q ₁ + α · Q ₁ = (1 + α) · Q ₁ (2)

In the thermal type flow meter constructed as described above,
Prior to the flow meter rule, when an instruction signal corresponding to the diversion ratio α set according to the measured flow rate range of the fluid is output from the input means, the diversion ratio setting circuit 16 causes the diversion ratio setting signal corresponding to the instruction signal. a is generated, and this shunt ratio setting signal a is output to the arithmetic circuit 14 and the control circuit 15.

The control circuit 15 outputs a control signal b corresponding to the diversion ratio setting signal a to the solenoid 12 to drive the valve body 11 to adjust the opening degree of the flow control valve 13 corresponding to the diversion ratio setting signal a. Let it set. Thereby, the diversion ratio α is determined.

With the split ratio α thus determined,
When the fluid is flown into the present thermal type flow meter while heating the heater 2 to measure the fluid, the temperature difference detection circuit 8 detects the upstream side and the downstream side detected by the upstream side and the downstream side temperature sensors 4 and 5, respectively. From the side detected temperatures T _a and T _b
T is obtained and the detected temperature difference ΔT is output to the arithmetic circuit 14.

Then, the arithmetic circuit 14 calculates the equation (1) based on the input data to obtain the flow rate Q ₁ passing through the sensor tube 1, and based on the flow rate Q ₁ and the diversion ratio α. The total flow rate Q is calculated by performing the calculation of the equation (2).
Will be asked.

Further, when setting the diversion ratio of a value different from the above-mentioned example, the diversion ratio is set by outputting an instruction signal corresponding to the diversion ratio of the value from the input means in the same manner as in the above-mentioned example. The circuit 16 outputs the diversion ratio setting signal a corresponding to the instruction signal to the control circuit 15, and the control circuit 15 outputs the flow control valve.
The opening degree is set by controlling 13 to obtain the desired diversion ratio.

By thus providing the flow control valve 13 on the bypass pipe 6 and adjusting the opening thereof easily, the ratio of the flow amount flowing through the sensor pipe 1 to the flow amount flowing through the bypass pipe 6,
That is, the diversion ratio can be easily adjusted. For this reason,
The measurement flow rate range can be expanded while maintaining highly accurate measurement. Further, in the conventional thermal type flowmeter using the shunt element, compared to the expansion of the measurement flow rate range achieved by replacing the shunt element, the control signal of the control circuit 15 is simply transmitted without such replacement of parts. Since this can be achieved by changing the size, the number of parts can be reduced correspondingly, and the workability in changing the diversion ratio can be improved.

In the above embodiment, the case where the volume flow rate is obtained has been taken as an example, but the same processing as above is performed even when obtaining the mass flow rate obtained by multiplying the volume flow rate by the density ρ. become.

In the above embodiment, the case where the control circuit 15 generates the control signal b according to the diversion ratio setting signal a and sets the opening of the flow control valve 13 in correspondence with the control signal b has been taken as an example. Alternatively, it may be configured as follows. That is, a signal indicating the detected temperature difference is input from the temperature difference detection circuit 8 to the control circuit 15, the shunt ratio setting signal a is input from the shunt ratio setting circuit 16, and the detected temperature difference is output from the temperature difference detection circuit 8. A control signal b is obtained by inputting and correcting the shunt ratio setting signal a by the detected temperature difference, and this control signal b is output to the solenoid 12 to drive the valve body 11 to correspond to the shunt ratio setting signal a. By doing so, the opening degree of the flow rate control valve 13 is set.

In the thermal type flow meter thus constructed, when the instruction signal corresponding to the diversion ratio α is input from the input means as shown in FIG. 3 (step S1), the control circuit 15 outputs the signal as described above. The control signal b corrected by the detected temperature difference ΔT with respect to the diversion ratio setting signal a is output to the flow control valve 13, so that the flow control valve 13 is opened by the control signal b of only the diversion ratio setting signal a. The opening E is set by adding the opening E _T obtained by the control signal b based on the detected temperature difference ΔT to E ₀ (step S2), and the flow rate of the sensor tube 1 is set with the opening E set in this way. On the other hand, Q ₁ and the detected temperature difference ΔT are obtained (step S3), while the detected temperature difference ΔT is fed back to the control circuit 15 to correct the opening degree of the flow control valve 13. Step
Subsequent to the processing of S3, the arithmetic circuit 14 carries out the operations of (1) and (2) (step S4) to obtain the total flow rate Q (step S5). In this case, since the feedback control is performed so as to adjust the opening degree of the flow rate control valve 13 according to the detected temperature difference ΔT, the flow rate can be measured more accurately according to the change in the flow rate.

Next, a thermal type flow meter according to a second embodiment of the present invention will be described with reference to FIGS. 4 and 5. This thermal type flow meter
Compared with the first embodiment shown in FIG. 1, a flow rate control valve 13 provided on the downstream side of the downstream side temperature sensor 5 in the sensor pipe 1 is provided instead of the flow rate control valve 13 provided on the bypass pipe 6. A proportional control circuit 20 in place of the diversion ratio setting circuit 16 and the control circuit 15, a diversion element 7 in the bypass pipe 6, and an amplifier circuit 9 on the output side of the temperature difference detection circuit 8. However, the other members are the same as those of the first embodiment, and the description of the same members will be omitted.

In this case, the proportional control circuit 20 inputs the upstream and downstream detected temperatures T _a and T _b detected by the upstream and downstream temperature sensors 4 and 5, respectively, and detects the detected temperature difference ΔT.
(ΔT = T _b −T _a ), the difference between the detected temperature difference ΔT and the preset reference temperature difference T ₀ is calculated to obtain difference data (T ₀ −ΔT), and the calculation of the following equation (3) is performed. Is performed to obtain the control amount E of the flow control valve 13. E = E + A (T ₀ −ΔT) (3) E: Control amount of flow control valve 13 A: Coefficient

Further, the proportional control circuit 20 controls the flow rate control valve 13 based on the control amount E so that the flow rate of the sensor tube 1 becomes constant, and the equation (8), which will be described later,
The calculation of (9) is performed to obtain the total flow rate Q. The processing contents of the proportional control circuit 20 will be described below.

When the detected temperature difference ΔT is larger than the reference temperature difference T ₀ , the flow rate Q ₁ is small (equation (1)).
Control) so that the opening is increased, and if the detected temperature difference ΔT is smaller than the reference temperature difference T ₀ , the flow rate Q ₁
Since there are many, the control is performed so that the opening degree is increased to secure a constant flow rate Q ₁ .

On the other hand, the differential pressure [Delta] P ₀ of the sensor tube 1, between the differential pressure [Delta] P of the differential pressure [Delta] P ₁ and the bypass pipe 6 in the flow control valve 13 a relationship of the following equation (4). ΔP ₀ + ΔP ₁ = ΔP (4)

Here, the flow rate of the flow control valve 13 is set to Q
₁ , and assuming that the flow rate flowing through the bypass pipe 6 is Q ₂ , there is a relationship of the following equations (5), (6), (7). _{ΔP 0 = 128μm 0 Q 1 /} (πd 0 4) ... ... (5) ΔP 1 = 128μm 1 Q 1 / (πd 1 4) ... ... (6) ΔP 2 = 128μm 2 Q 2 / (πd 2 4) ... (7) μ: viscosity d ₀ : inner diameter of sensor tube 1 m ₀ : length of sensor tube 1 d ₁ : equivalent diameter of flow control valve 13 m ₁ : equivalent length of flow control valve 13 d ₂ : bypass pipe Equivalent diameter of 6 m ₂ : Equivalent length of bypass pipe 6

Further, the total flow rate Q flowing into the present thermal type flow meter
Is the flow rate through the flow control valve 13 to flow through the Q _1, the bypass pipe 6 can be obtained as the sum of the Q _2, total flow rate Q based on and each of the formulas above have such relationship
Is obtained by the following equation (8). Q = Q ₁ + Q ₂ = Q ₁ [1+ (m ₀ / m ₂ ) (d ₂ ⁴ / d ₀ ⁴ )] + Q ₁ [1+ (m ₁ / m ₂ ) (d ₂ ⁴ / d ₁ ⁴ )] ... … (8)

Here, by making the flow rate Q ₁ constant as described above, m ₀ , m ₁ , m ₂ , d ₀ , d ₂ are fixed values, so the total flow rate Q is expressed by the following equation (9). It will be found in. Q = G ₁ + G ₂ / d ₁ ⁴ (9) G ₁ and G ₂ : constants

That is, the proportional control circuit 20 controls the opening of the flow rate control valve 13 so that the flow rate of the flow rate control valve 13 becomes constant, and the control valve equivalent diameter d ₁ ⁴ achieved by this control is achieved.
The total flow rate Q will be detected from the change amount of.

In the thermal type flow meter thus constructed, as shown in FIG. 5, first, the reference temperature difference T ₀ is set (step S10), and the temperature difference detecting circuit 8 detects the upstream side and the downstream side. The detected temperature difference ΔT is obtained based on the temperatures T _a and T _b (step S11). When this is output to the comparison control circuit 20,
The comparison control circuit 20 calculates E = E + A (T ₀ −ΔT) (step S12) to obtain the control amount E of the flow rate control valve 13 (step S13), and supplies this control amount E to the flow rate control valve 13. The flow rate is controlled by controlling the flow rate control valve 13 so that the flow rate flowing through the sensor tube 1 becomes constant (step S14), and the total flow rate Q is calculated by performing the operations of the equations (8) and (9). Step S15).

As described above, since the flow rate control valve 13 is provided in the sensor pipe 1 and the opening degree thereof can be adjusted to change the diversion ratio, the measurement flow rate range in the fluid flow rate measurement can be expanded. When the flow rate flowing through the sensor tube 1 changes, the temperature rise of the fluid with respect to a constant heating amount by the heater 2 becomes different, so that the flow rate control valve 13 is provided in the sensor tube 1 as in the present embodiment.
In order to make the obtained flow rate value proper, it is necessary to take measures such as providing the arithmetic circuit 14 with means for correcting the data in calculating the flow rate value. In addition, since the flow rate of the sensor tube 1 is kept constant, the flow rate of the fluid can be measured with high accuracy without providing the above-described data correction means.

In each of the above embodiments, the case where the valve body of the flow control valve is needle-shaped has been taken as an example, but the present invention is not limited to this, and may be flat-shaped, for example.

[0040]

Since the present invention is the thermal type flow meter configured as described above, the flow dividing ratio is adjusted by adjusting the opening degree of the flow rate control valve provided in at least one of the pipe and the bypass pipe. Can be adjusted, so that the measurement flow rate range can be easily expanded without replacement of parts. Further, the number of parts can be reduced correspondingly by expanding the measurement flow rate range without exchanging parts and the workability can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a thermal type flow meter according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an opening degree / flow rate characteristic of a flow rate control valve of the same thermal type flow meter.

FIG. 3 is a flowchart showing an operation example of a thermal type flow meter of a type used to feed back output data of a temperature difference detection circuit and control the flow rate control valve.

FIG. 4 is a diagram schematically showing a thermal type flow meter according to a second embodiment of the present invention.

FIG. 5 is a flowchart showing an operation example of the same thermal type flow meter.

FIG. 6 is a diagram schematically showing an example of a conventional thermal type flow meter.

[Explanation of symbols]

 1 Sensor Pipe 2 Heater 4 Upstream Temperature Sensor 5 Downstream Temperature Sensor 6 Bypass Pipe 13 Flow Control Valve

Claims (1)

[Claims] 1. A heating element is attached to a pipe through which a fluid passes, and upstream and downstream temperature detecting means are provided on the upstream side and the downstream side of the heating element of the pipe, respectively, so that both temperature detecting means are bypassed. A thermal type flow meter in which a bypass pipe is provided in the pipe, wherein a flow control valve is provided in at least one of the pipe and the bypass pipe.