JPH11142198A - Flowmeter making use of flow sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a flowmeter, making use of a flow sensor, which measures not only a large flow rate but also a small flow rate by using one flow sensor, whose constitution is simplified, whose accuracy is high, whose durability is enhanced and whose costs are reduced. SOLUTION: A selector valve 2 is built in a large-diameter tube 1 in which a fluid to be measured flows. A small-diameter tube 3 is installed so as to bypass the selector valve 2. A flow sensor 4 is built in the small-diameter tube 3. Then, when the flow rate of the fluid, to be measured, flowing inside the large-diameter tube 1 is at a set value or lower, the selector valve 2 is closed, the fluid to be measured is made to flow to the side of the small-diameter tube 3, and the flow rate is detected directly by the flow sensor 4. When the flow rate to be detected by the flow sensor 4 is at the set value or higher, the selector valve 2 is opened, the fluid to be measured is made to flow to the side of the large-diameter tube 1, the small-diameter tube 3 is used as a Pitot tube, and the flow rate is detected by the flow sensor 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the flow rate of a gas, in which a large flow rate is detected (measured) indirectly by a pitot tube method using a single flow sensor, and a small flow rate is measured by the flow sensor. The present invention relates to a flowmeter that directly detects (measures) using the flowmeter.

[0002]

2. Description of the Related Art In the case of a flow meter for detecting a gas flow rate using a flow sensor, a small diameter pipe for measuring a small flow rate and a large diameter pipe for measuring a large flow rate are separately provided. In general, a method of incorporating a small flow rate and flowing a fluid through a small diameter pipe, and a flow rate of a large flow rate through a large diameter pipe and detecting them separately are common.

[0003] When detecting the flow rate with a flow sensor, especially when the flow rate is small, it is necessary to reduce the pipe diameter and increase the flow velocity around the flow sensor to make the flow velocity higher than the detection sensitivity of the flow sensor. On the other hand, when the flow rate is large, if the pipe diameter is small, the pressure loss becomes large and the passage of the measurement fluid is hindered. Therefore, it is necessary to increase the pipe diameter.

[0004]

Therefore, flow sensors are provided in both the large and small pipes, and two amplifier circuits and the like are required for the flow sensors, so that the entire apparatus becomes complicated and expensive. There is no problem. In addition, when the flow rate is large, impurities such as dust remaining in the piping system are likely to be mixed into the measurement fluid, and this adheres to the sensor main body, thus deteriorating measurement accuracy.

[0005] The present invention is proposed in view of the above-mentioned point, and a small flow rate is directly detected by a flow sensor, and a large flow rate is detected by the same flow sensor using the Pitot tube principle. It is an object of the present invention to provide a flow meter that uses only one sensor and does not deteriorate the detection accuracy of the flow sensor due to dust or the like.

[0006]

According to the present invention, a flow meter utilizing a flow sensor provided to achieve the above object is as follows. 1. A switching valve is incorporated in the large-diameter pipe through which the fluid to be measured flows, a small-diameter pipe is provided to bypass the switching valve, and a flow sensor is incorporated in the small-diameter pipe so that the flow rate of the fluid flowing through the large-diameter pipe is equal to or less than a predetermined value. In the case of, when the flow rate is directly detected by the flow sensor by flowing the fluid to the small-diameter pipe side by closing the switching valve, and when the flow rate detected by the flow sensor becomes a certain value or more, the Open the switching valve and let the fluid flow to the large diameter pipe side,
A flow meter using a flow sensor including a microcomputer section that controls the flow sensor to detect a flow rate using the small-diameter pipe as a pitot tube and that calculates a flow rate based on an output from the flow sensor. .

[0007] 2. 2. The flow meter according to claim 1, wherein the upstream opening of the small-diameter pipe is directed upstream in the large-diameter pipe so that dynamic pressure acts on the opening. 3. The small-diameter pipe is bent at right angles or in a circular shape in the large-diameter pipe so that the upstream opening is parallel to the axial direction of the large-diameter pipe, and dynamic pressure acts on this opening. 3. A flow meter using the flow sensor according to the above item 2.

[0008] 4. 3. A flow meter using a flow sensor according to the above item 2, wherein an opening of a small-diameter pipe projecting into a large-diameter pipe is cut obliquely so that dynamic pressure acts. 5. A flowmeter using the flow sensor according to the above 2, wherein a fluid inlet is formed toward the upstream side in the small-diameter pipe protruding into the large-diameter pipe, and dynamic pressure acts on the fluid inlet. .

6. A circuit for storing the open or closed state of the switching valve is provided in the microcomputer unit, and when the switching valve is closed, the flow sensor directly detects the flow rate of the fluid,
When the switching valve is open, the flow sensor detects the flow rate generated by the dynamic pressure and the static pressure in the small diameter pipe, judges that the flow rate flowing in the large diameter pipe is detected, and calculates the flow rate at that time 6. A flow meter using the flow sensor according to the above 1 or 2 or 3 or 4 or 5, wherein

[0010] 7. A circuit for confirming the open or closed state of the switching valve is provided in the microcomputer unit, and when the switching valve is closed, the flow sensor directly detects the flow rate of the fluid,
When the switching valve is open, the flow sensor detects the flow rate generated by the dynamic pressure and the static pressure in the small diameter pipe, judges that the flow rate flowing in the large diameter pipe is detected, and calculates the flow rate at that time 6. A flow meter using the flow sensor according to the above 1 or 2 or 3 or 4 or 5, wherein

8. 8. A flow meter using the flow sensor according to the above 1 or 6, wherein the downstream end of the small-diameter pipe projects into the large-diameter pipe, and the opening of the small-diameter pipe is set to face the upstream side.

[0012]

The switching valve in the large-diameter pipe is opened and closed by the microcomputer. When the value of the flow rate flowing through the large-diameter pipe detected by the method using the small-diameter pipe as a pitot tube falls below the reference value, the microcomputer closes the switching valve and flows the fluid to the small-diameter pipe side, and the flow rate is directly measured by the flow sensor. Is detected. Also,
When the flow rate directly detected by the flow sensor exceeds the reference value, the microcomputer opens the switching valve to switch the flow to the large diameter side.

[0013]

Embodiment 1 In this embodiment, as shown in FIG. 1, a switching valve 2 is mounted in a large-diameter pipe 1 and a small-diameter pipe 3 is provided so as to bypass the switching valve 2. 3 has a flow sensor 4 incorporated therein. The opening 3a on the upstream side of the small diameter pipe 3 is bent at a right angle so as to face the upstream side of the large diameter pipe 1 as shown in FIG. Alternatively, a dynamic pressure is applied by cutting diagonally as shown in (c) or by providing an inflow port 3c toward the upstream side as shown in (d). On the other hand, a static pressure acts on the downstream opening 3b.

In the figure, reference numeral 2a denotes an actuator for operating the switching valve 2, and 5 denotes a microcomputer.
Switches the switching valve 2 according to the flow rate in the large diameter pipe 1 and the flow rate in the small diameter pipe 3,
Calculates the flow rate based on the output from, and outputs it to the display 6.

The operation and measurement example of this embodiment will be described with reference to FIGS. FIG. 3 shows a state in which a small flow rate is measured, in which the switching valve 2 is closed, all of the fluid flows into the small-diameter pipe 3 from the opening 3a, and returns to the large-diameter pipe 1 from the opening 3b. The flow sensor 4 directly detects the flow rate in the small diameter pipe 3 and outputs this value to the microcomputer unit 5 side. The microcomputer unit 5 calculates the flow rate based on the output.

When the flow rate reaches a predetermined flow rate, the switching valve 2 opens according to a command from the microcomputer unit 5. In FIG. 4, the opening 3a of the small-diameter tube 3 faces the axis of the flow, while the opening 3b on the downstream side opens at right angles to the axis. The flow is generated in the small-diameter pipe 3 by the dynamic pressure, and the flow sensor 4 detects the flow, and outputs this to the microcomputer unit 5. The microcomputer unit 5 calculates the flow rate based on the output.

When the flow sensor 4 detects the flow rate in each of the open and closed states of the switching valve 2, the flow rate passing through the entire flow meter uniquely corresponds in a fixed relation. By storing the data in the microcomputer unit 5, a flow meter can be obtained.

More specifically, a measurement example in the case of the present embodiment will be described in detail with reference to FIGS. When the flow rate is small, the flow through the small diameter pipe 3 is directly detected as shown in FIG. 3, but when a certain flow rate Q1 is reached, the switching valve 2 is opened as shown in FIG. The flow generated by the differential pressure of the opening 3b is detected. At this time, in FIG. 4, Pu: upstream pressure of small diameter pipe 3 dynamic pressure (generated by flow QL) + static pressure Pd: downstream pressure of small diameter pipe 3 Static pressure R: resistance of flow of small diameter pipe 3 (Pu−Pd) / R: Flow in small diameter pipe caused by dynamic pressure

FIG. 5 shows the output of the flow sensor 6. The solid line indicates the flow rate increase and the broken line indicates the flow rate decrease. By setting the operating flow rate of the switching valve 2 to Q1 when rising and Q2 when falling, and having a hysteresis characteristic, a hunting phenomenon that frequently opens and closes near the switching flow rate, etc. To prevent it. The relationship between the sensor output value and the actual flow rate is determined in advance by an experiment, and this function is stored in the microcomputer unit 5. In actual measurement, the sensor output is calculated and displayed using this function, thereby providing a flow meter.

The switching flow rates Q1 and Q2 can be arbitrarily set for control by the microcomputer unit 5, and it is desirable to reduce the switching frequency as much as possible for durability of the switching valve 2 and the like. It is better to set a large value. However, on the other hand, the pressure loss curve is substantially the same as the output of the flow sensor 4 shown in FIG.
The upper limit of the switching flow rate is determined by the allowable maximum pressure loss. Generally, the pressure loss at the maximum flow rate is determined by the cross-sectional area of the large-diameter pipe 1, and the pressure loss at the switching flow rate is determined by the cross-sectional area of the small-diameter pipe 3. Therefore, it is necessary to determine these constants according to required specifications. .

[0021]

Embodiment 2 This embodiment is shown in FIG. In the present embodiment, the opening 3b on the downstream side of the small diameter pipe 3 is opened toward the upstream side by the same method as that shown in FIG. 2, and the opening 3a on the upstream side is opened toward the axial direction. In this case, since the flow near the flow sensor 4 at the time of large flow rate measurement with the switching valve 2 opened is in the reverse direction, if the flow sensor 4 can also detect the flow velocity in the reverse direction, an output curve as shown in FIG. Becomes

In this case, if the output potential is in the opposite direction, it can be understood that the large flow rate measurement with the switching valve 2 open is obtained.
The microcomputer unit 5 does not need to recognize the open / closed state of the switching valve 2 each time, which is simple. Further, according to the present embodiment, a rational design in which the forward and reverse sensitivities of the flow sensor 4 are different so that the design has the optimum sensitivity for each of the small flow rate and the large flow rate measurement. It is also possible to use

[0023]

According to the present invention, a flow meter for measuring a flow rate with a flow sensor by the above configuration and operation is provided.
The following effects are obtained. 1. At the time of measuring a large flow rate, by making the small-diameter pipe function as a pitot tube, the detection of the small flow rate and the large flow rate can all be performed by one flow sensor attached to the small-diameter pipe.
As a result, there is no need to use two measurement systems as in the related art.

2. Since the flow sensor is built into a small-diameter pipe, even if dust or the like is mixed in the measurement fluid at a large flow rate, only a minute flow due to dynamic pressure acts on the flow sensor. High precision, durability and reliability can be secured without dust entering.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a flow meter according to a first embodiment.

FIG. 2 is an explanatory view of an embodiment of an opening.

FIG. 3 is an explanatory diagram of a state in which a small flow rate is directly detected by a flow sensor.

FIG. 4 is an explanatory view showing a state in which a switching valve is opened and a flow sensor detects a large flow rate by a pitot tube method.

FIG. 5 is an explanatory diagram of a flow sensor output and a switching valve opening / closing timing.

FIG. 6 is an explanatory diagram of a flow meter according to a second embodiment.

FIG. 7 is an explanatory diagram of a flow sensor output according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Large diameter pipe 2 Switching valve 2a Actuator 3 Small diameter pipe 3a Opening 3b Opening 3c Inflow port 4 Flow sensor 5 Microcomputer part 6 Display part

Claims (8)

[Claims] 1. A switching valve is incorporated in a large-diameter pipe through which a fluid to be measured flows, a small-diameter pipe bypassing the switching valve is provided, and a flow sensor is incorporated in the small-diameter pipe so that a fluid flowing through the large-diameter pipe can be measured. When the flow rate becomes equal to or less than a certain value, the switching valve is closed to flow the fluid to the small-diameter pipe side, and the flow rate is directly detected by the flow sensor, and the flow rate detected by this flow sensor becomes equal to or more than a certain value. In this case, the switching valve is opened to flow the fluid to the large-diameter pipe side, the small-diameter pipe is used as a pitot tube, and the flow sensor is controlled to detect the flow rate, and the output from the flow sensor is output. A flow meter using a flow sensor provided with a microcomputer unit for calculating a flow rate based on the flow rate. 2. The flow sensor according to claim 1, wherein an opening on the upstream side of the small-diameter pipe is directed upstream in the large-diameter pipe so that dynamic pressure acts on the opening. Flow meter used. 3. A small-diameter pipe is bent at right angles or in a circle in a large-diameter pipe so that an upstream opening is parallel to an axial direction of the large-diameter pipe, and dynamic pressure is applied to the opening. 3. A flow meter utilizing a flow sensor according to claim 2, wherein said flow meter is configured to operate. 4. A flow meter using a flow sensor according to claim 2, wherein the opening of the small-diameter pipe projecting into the large-diameter pipe is cut obliquely so that dynamic pressure acts. 5. The flow according to claim 2, wherein in the small-diameter pipe projecting into the large-diameter pipe, a fluid inlet is formed toward the upstream side, and a dynamic pressure is applied to the fluid inlet. A flow meter using a sensor. 6. A microcomputer is provided with a circuit for storing the open or closed state of the switching valve. When the switching valve is closed, the flow sensor directly detects the flow rate of the fluid. When the flow sensor detects the flow velocity generated by dynamic pressure and static pressure in the small diameter pipe, it is determined that the flow rate flowing in the large diameter pipe is detected, and the flow rate at that time is calculated. A flow meter using the flow sensor according to claim 1 or 2 or 3 or 4 or 5. 7. A microcomputer is provided with a circuit for confirming whether the switching valve is open or closed. When the switching valve is closed, the flow sensor directly detects the flow rate of the fluid. When the flow sensor detects the flow velocity generated by dynamic pressure and static pressure in the small diameter pipe, it is determined that the flow rate flowing in the large diameter pipe is detected, and the flow rate at that time is calculated. A flow meter using the flow sensor according to claim 1 or 2 or 3 or 4 or 5. 8. The flow sensor according to claim 1, wherein the downstream end of the small-diameter pipe projects into the large-diameter pipe, and the opening of the small-diameter pipe is set to face the upstream side. Flow meter using.