JPH11160126A - Flow adjustment method - Google Patents

Abstract

(57) Abstract: A flow rate adjusting method using a flow rate adjusting device including a fluid differential pressure measuring means and a flow path changing means. A relationship between a flow rate change amount and a flow rate is measured in a measurable high flow rate region. The relationship between the flow path change amount and the flow rate is calculated in a low flow rate range where measurement is not possible. The relationship between the flow rate change amount and the flow rate in the transition section area from the low flow rate area to the high flow rate area is determined from the measurement result and the calculation result as a composite value, and the flow rate in the transition section area is controlled. The composite value Q ₁ ′ of the flow rate in the transition section area is obtained by the following equation. Q ₁ '= Q ₂ × (XX ₁ ) / (X ₂ -X ₁ ) + Q ₁ ×
_{(X 2 -X) / (X} 2 -X 1) However, Q _1: flow rate calculation value in the flow rate setting value X Q _2: flow rate measurements in the flow rate setting value X X: flow rate set value X _1: transition section lower X ₂ : Transition section upper limit

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to fluid flow control, and more particularly to a flow control method capable of accurately controlling the flow of a low-pressure fluid in a low flow rate range.

[0002]

2. Description of the Related Art In general, a flow meter using a differential pressure generating mechanism using a throttle mechanism such as an orifice or a venturi,
In the measurement in the low flow rate range (about 20% or less of the maximum measurable flow rate), there is a problem that the measurement error increases rapidly as the flow rate decreases, and the variation also increases, resulting in poor reliability.

[0003] The differential pressure type flow measuring device comprises a differential pressure generating mechanism,
A differential pressure transmitter connected to this mechanism to generate an electric signal proportional to the differential pressure, and a square root calculator that outputs a signal proportional to the measured flow rate by performing a square root operation on the electric signal from the differential pressure transmitter; A multiplier that multiplies a signal proportional to the measured flow rate by a predetermined coefficient is widely used.
The relationship between the flow rate of the flow rate measuring device and the differential pressure is represented by F = K√ΔP, as shown in FIG.

However, F: flow rate, ΔP: differential pressure, K: flow rate coefficient K is a constant value determined by the shape of the differential pressure generating mechanism, fluid conditions, and the like. However, this flow rate measuring device has a drawback that the flow rate-differential pressure characteristic shown in FIG. 6 tends to deviate from the square characteristic in a low flow rate range, and the measurement accuracy in the low flow rate range is poor. For this reason, a bypass pipe through which fluid flows in a low flow rate region is provided, and another differential pressure generating mechanism is installed in this bypass pipe, and the system after the differential pressure transmitter is selectively used in a high-low double range. There are drawbacks that make it more complicated.

In order to solve such a problem, conventionally,
The following flow rate correction method for a low flow rate region has been proposed. Japanese Patent Application Laid-Open No. 56-29120 discloses a flow measurement method (hereinafter referred to as "prior art 1"): In prior art 1, a constant arithmetic expression is obtained from measured values of differential pressure, liquid pressure, and temperature before and after a throttle mechanism. Based on the density correction and square root calculation based on the obtained flow rate measurement value, the flow rate measurement value is calculated by performing a calculation correction based on a certain relational expression between the flow coefficient and the flow rate corresponding to the flow rate measurement value obtained as a result. This is a method of obtaining the measured flow rate by correcting. As shown in FIG. 7, a differential pressure generating mechanism 12 is provided in a pipe 11 for transporting a fluid, and a differential pressure transmitter 13 is connected to the differential pressure generating mechanism 12. An electrical signal proportional to the differential pressure ΔP is output from the differential pressure transmitter 13, and the square root of the output is obtained by the square root calculator 14. Square root calculator 14
Is a signal proportional to the measured flow rate, and this signal Fm
Is given to the function calculator 15 and the multiplier 16. The function calculator 15 outputs a flow coefficient K expressed as a function of the input Fm. The calculated flow coefficient K is provided to a multiplier 16, which multiplies the signal FM by the flow coefficient K to output a flow signal FT.

As shown in FIG. 8, a function calculator 15 calculates a flow coefficient K expressed by the ratio of the true flow rate FT to the measured flow rate Fm.
Is set in advance, and outputs a constant value K0 when the set flow rate is equal to or higher than F0, but outputs a gradually increased value when the set flow rate is equal to or lower than F0. The curve shown in FIG. 8 is uniquely determined by the throttle ratio of the differential pressure generating mechanism 12 and the Reynolds number of the fluid, and can be easily set in the function calculator 15.

In the prior art 1, the error increases with the flow rate in the low flow rate region, and the measurement can be performed with high accuracy even in the flow rate range where measurement was impossible.
%).

[0008] Japanese Patent Application Laid-Open No. 54-158264 discloses a differential pressure type flow rate measuring device (hereinafter referred to as "prior art 2"): the prior art 2 comprises a differential pressure across the throttle mechanism and the differential pressure connected to the mechanism. A differential pressure transmitter that generates an electric signal proportional to the differential pressure transmitter; a square root calculator that outputs a signal proportional to the measured flow rate by performing a square root operation on the electric signal from the differential pressure transmitter; a true flow value and a measured flow value A flow coefficient represented by the ratio is set in advance, and a function calculator that receives an output signal of the square root calculator and calculates a required flow coefficient, and an output signal of the square root calculator to the function calculator of the function calculator And a multiplier that outputs a flow signal by multiplying the output signal.

According to the prior art 2, it is possible to accurately measure the flow rate in a low flow rate range under one differential pressure generating mechanism. Therefore, the flow coefficient that greatly affects the measurement result can be corrected in accordance with the flow rate, so that measurement can be performed with high accuracy up to a low flow rate range.

[0010]

The prior art described above employs a method of obtaining a measured value, even though there is an error, and correcting the measured value by various methods when measuring in a low flow rate region. Therefore, in the case of a low-pressure fluid that requires an ultimate pressure (pressure on the secondary side of the flow control mechanism) exceeding a certain value, the possible differential pressure generated by the differential pressure generating mechanism (in the high flow rate range) The maximum pressure) is limited, and the throttle cannot be freely increased. As a result, the differential pressure becomes weak in a low flow rate region, and as a result, the flow rate cannot be measured. FIG. 5 is a graph showing a relationship between a flow rate set value and each flow rate value according to the conventional flow rate adjusting method. In FIG. 5, Q ₂ : flow rate measurement value at flow rate setting value X X: flow rate setting value X ₁ : lower limit of measurable As shown in FIG. 5, in the related art, the low flow rate area is an uncontrollable range. In such a case, a bypass pipe through which a fluid flows in a low flow rate area is provided, and another differential pressure generating mechanism is installed in the bypass pipe, and the method must be used in a high flow rate area and a low flow rate area. . However, this has a problem that the device configuration and operation are complicated.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a flow rate adjusting method capable of easily and widely controlling a flow rate of a low-pressure fluid with only one differential pressure generating mechanism. Is to provide.

[0012]

According to the first aspect of the present invention,
In a flow rate adjusting method using a flow rate adjusting device including a fluid differential pressure measuring means and a flow rate changing means, a relationship between a flow rate change amount and a flow rate is measured in a measurable high flow rate area, and in a low flow rate area where measurement is impossible. The relationship between the flow rate change amount and the flow rate is calculated, and the relationship between the flow rate change amount and the flow rate in the transition section area from the low flow rate area to the high flow rate area is calculated from the measurement result and the calculation result as a composite value. , Characterized in that the flow rate in the transition section area is controlled by the composite value.

According to a second aspect of the present invention, in the method according to the first aspect, a combined value Q ₁ ′ of the flow rate in the transition section area is represented by the following equation: Q ₁ ′ = Q ₂ × (XX ₁ ) / ( X ₂ −X ₁ ) + Q ₁ ×
(X ₂ −X) / (X ₂ −X ₁ ) where Q ₁ : Flow rate calculation value at flow rate setting value X Q ₂ : Flow rate measurement value at flow rate setting value X X: Flow rate setting value X ₁ : Transition section lower limit X ₂ : Characteristic in that it is determined by the upper limit of the transition section.

When the flow rate of a low-pressure fluid is controlled by a flow rate control mechanism including a differential pressure generating mechanism (orifice or venturi) and a flow rate control valve, flow rate control is generally performed in a low flow rate region because the generation of a differential pressure is weak. Although it is difficult in terms of flow, by previously setting the relationship between the opening degree of the flow control valve and the flow rate, it is possible to control the flow rate in a wide range from a low flow rate range to a measurable high flow rate range.

[0015]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing a device configuration of a flow rate adjusting device according to an embodiment of a flow rate adjusting method of the present invention. In FIG. 1, 1 is a flow control valve (including an opening degree meter), 2 is a differential pressure type flow meter (orifice or venturi), 3 is a thermometer, and 4 is a pressure gauge. FIG. 2 is a graph showing a relationship between a flow rate and a flow rate set value according to the embodiment of the present invention. In FIG. 2, Q ₁ : a calculated flow value at the flow rate set value X Q ₂ : a measured flow rate at the flow rate set value X X: a flow rate set value X ₁ : a transition section lower limit X ₂ : a transition section upper limit As shown in FIG. The flow rate Q ₁ ′ in the transition section (area A) from the low flow rate area to the high flow rate area is controlled by the values of Q ₁ , Q ₂ , X, X ₁ and X ₂ .

Area flow rate = Q ₁ Area flow rate = Q ₂ Area A flow rate = Q ₁ ′ = Q ₂ × (XX ₁ ) / (X ₂ -X ₁ ) + Q ₁ × (X ₂ -X) / (X ₂ −X ₁ ) (1) As shown in FIG. 2, by controlling the flow rate by the above equation (1), the region A is connected almost linearly from the lower limit X ₁ to the upper limit X _2. , Smooth and continuous over a wide range from a low flow rate range to a measurable high flow rate range.

[0017]

Next, an embodiment of the present invention will be described. FIG.
FIG. 4 is a graph showing the relationship between the elapsed time and the flow rate (process value) according to the embodiment of the present invention. FIG. 4 is a graph showing the relationship between the set flow rate and the flow rate (process value) in the transition section from the low flow rate range to the high flow rate range. It is a graph which shows a relationship.

The specifications of the embodiment are as follows. Fluid type: oxygen Flow control mechanism inlet pressure: 500 mmAq Flow control range: 0 to 20000 Nm ³ / h Flow measurement actual measurement range: 4000 Nm ³ / h or more Fluid temperature: normal temperature to 70 ° C. The control area was as follows.

The low flow rate zone: 0~5000Nm ³ / h; the valve opening control transition section area calculated value by: 5000~6000Nm ³ / h; control high flow rate range the combined value by the present invention the flow rate adjusting method: 6000 nm ³ / h: Controlling the measured flow rate As shown in the drawing, even in the transition section area of 5000 to 6000 Nm ³ / h, it is connected almost linearly and smoothly and continuously over a wide range from a low flow rate area to a measurable high flow rate area. Was measured.

[0020]

As described above, according to the present invention, the flow rate can be continuously controlled over a wide range from a low flow rate range to a high flow rate range without adding a new device to the conventional flow rate control mechanism. Configuration, simplifying the device,
The control range can be easily expanded even in the existing flow control mechanism, and thus a useful effect is provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a device configuration of a flow rate adjusting device according to an embodiment of a flow rate adjusting method of the present invention.

FIG. 2 is a graph showing a relationship between a flow rate set value and each flow rate value according to the embodiment of the flow rate adjusting method of the present invention.

FIG. 3 is a graph showing an outline of a relationship between an elapsed time and a flow rate (process value) according to the embodiment of the flow rate adjusting method of the present invention.

FIG. 4 is a graph showing a relationship between a set flow rate and a flow rate (process value) in a transition section from a low flow rate range to a high flow rate range according to the embodiment of the flow rate adjusting method of the present invention.

FIG. 5 is a graph showing a relationship between a flow set value and each flow value according to the related art.

FIG. 6 is a graph showing a relationship between a differential pressure and a flow rate.

FIG. 7 is a block diagram showing a differential pressure type flow measurement device.

FIG. 8 is a graph showing a relationship between a measured flow rate and a flow coefficient.

[Explanation of symbols]

 1: Flow control valve (including opening meter) 2: Differential pressure flow meter (orifice or venturi) 3: Thermometer 4: Pressure gauge 11: Piping 12: Differential pressure generating mechanism 13: Differential pressure transmitter 14: Square root calculator 15: Function calculator 16: Multiplier

Claims (2)

[Claims] In a flow rate adjusting method using a flow rate adjusting device including a fluid differential pressure measuring means and a flow rate changing means, a relationship between a flow rate change amount and a flow rate is measured in a measurable high flow rate range, and measurement is impossible. The relationship between the flow rate change amount and the flow rate in a low flow rate region is calculated, and the relationship between the flow rate change amount and the flow rate in the transition section region from the low flow rate region to the high flow rate region from the measurement result and the calculation result. Is obtained as a composite value, and the flow rate in the transition section area is controlled by the composite value. 2. A composite value Q ₁ ′ of the flow rate in the transition section area.
To the following formula: Q ₁ ′ = Q ₂ × (XX ₁ ) / (X ₂ −X ₁ ) + Q ₁ ×
(X ₂ −X) / (X ₂ −X ₁ ) where Q ₁ : Flow rate calculation value at flow rate setting value X Q ₂ : Flow rate measurement value at flow rate setting value X X: Flow rate setting value X ₁ : Transition section lower limit X ₂ : The flow rate adjusting method according to claim 1, wherein the flow rate adjusting method is determined by an upper limit of a transition section.