JPS5973726A - Flow rate detecting device - Google Patents

Abstract

PURPOSE:To obtain a flow rate accurately even under the state the flow of cryogenic evaporating fluid is hardly found, by omitting the use of orifice, and detecting the flow rate by using a Cv value based on the valve lift of a flow regulating valve, which regulates the flow rate, and the differential pressure between the fluid pressures at the upstream and downstream sides in the vicinity of the flow regulating valve. CONSTITUTION:A fluid flowing in a pipe 1 is changed by the operation of the valve lift of a flow regulating valve 6, which is driven by a control device that is separately provided. A valve lift detecting device 14 detects the valve lift of the flow regulating valve 6, and sends the output signal to a Cv function generator 15 as an input, in order to generate the function of the Cv value, which is inherent to said valve. Meanwhile, fluid pressures PU and PL at the upstream and downstream sides of the flow regulating valve 6, which are transmitted to pressure transducers 9 and 11 through pressure pipes 8 and 10, are transduced into electric signals. The signals are inputted into a deviation device 12. The differential pressure PU-PL, which is obtained by the deviation device 12, is inputted into a square root extracting device 13, and the square root of the absolute value is extracted. The result is inputted to a multiplier 16, where the Cv value and a constant are multiplied, and a flow rate Q is obtained. In this device, the flow regulating valve 6 itself is used as a throtlling mechanism.

Description

[Detailed description of the invention] The present invention relates to a detection device.

When determining the flow rate of fluid flowing in a piping flow path. Usually an orifice is used.

That is, as shown in FIG.
Interposed. Fluid pressure near the orifice 2 on the upstream and downstream sides is guided to a differential pressure gauge 5 through impulse pipes 3 and 4. The output of the differential pressure gauge 5 is converted into a flow rate based on a predetermined relationship such as the Reynolds number, and the two converters 7 output the flow rate.

For example, in the device constructed in this manner, '0. When measuring the flow rate of a cryogenic evaporation main liquid fluid such as body nitrogen,
It may also be a problem.

The flow control valve 6 installed in the pipe 1 is almost fully closed. Problems occur when there is almost no flow. After all, although the piping 1 and the impulse pipe 34 are wrapped with heat insulating material, some amount of heat cannot be avoided. Therefore, when there is almost no flow, the liquid around the orifice 2 will vaporize due to heat input from the impulse pipes 3 and 4, etc.
Air bubbles are generated locally. As a result, the differential pressure transmitted to the differential pressure gauge 5 often fluctuates abnormally.

However, when measuring the flow rate using a throttle mechanism such as the orifice 2, the flow rate is proportional to the square root of the differential pressure.

Since the opening area of the orifice 2 is constant, the differential pressure cannot be particularly increased.

When the flow rate is low, a small differential pressure is used, and abnormal fluctuations in pressure due to the generation of bubbles result in extremely large detection errors, further aggravating the above-mentioned problems.

This will impede the stability and reliability of flow measurement.

The present invention eliminates these drawbacks, and provides a device for measuring the flow rate of fluid flowing in a flow path restricted by a flow rate control valve, which includes a valve lift detection method for detecting the valve lift of the flow rate control valve. a Cv function generator that generates a unique Cv value of the flow control valve based on the valve lift; and a deviation device that measures the pressure difference between the pressure on the upstream and downstream sides of the flow control valve; It is characterized by comprising a square root operator that squares the absolute value of the value obtained by the deviation device, and a multiplier that multiplies the square root operator and the output of the Cv function generator and a constant,
The purpose of this invention is to provide a flow rate detection device that can accurately determine the flow rate of cryogenic evaporated main liquid even when there is almost no flow.

In other words, the device of the present invention eliminates the use of an orifice,
The flow rate is detected by using the so-called Cv value, which is used for the valve lift of the flow rate control valve that adjusts the flow rate, and the differential pressure between the fluid pressures on the upstream and downstream sides near the flow rate control valve.

Therefore, in cases where there is almost no flow.

By narrowing the opening of the flow control valve, the pressure difference between the upstream and downstream sides can be increased.

Even when air bubbles generated by pressure waves move and cause slight fluctuations in differential pressure, it is possible to minimize flow rate detection errors.

The present invention will now be described with reference to an embodiment of the apparatus shown in FIG.

Reference numeral 1 denotes a pipe through which a fluid flows, and a flow rate control valve 6 is interposed therein, and a pair of impulse pipes 8 and 1o are opened near the upper and downstream sides thereof. 9 and 11 are pressure transducers for measuring the fluid pressures Pa and PL guided by the pressure impulse pipes 8 and 1o,
The output is introduced into the deviation device 12 and the differential pressure PU-PL is detected.

Reference numeral 13 denotes a square root computing unit which squares the absolute value of the differential pressure PU - PL detected and detected by the deviation device 12, and includes a multiplier 1 to be described later.
6, the values Jl-'p, , '-PLl are output.

14 is a valve lift detector that detects the valve lift of the flow rate control valve 6; 1 is a valve lift detector that detects the specific Cv of the flow rate control valve 6 based on the valve lift;
This is a Cv function generator that generates a value, and stores a function between valve lift and Cv value as shown in FIG.

16 is the output J l'Pg -Pl of the square root calculator 13;
l, an arithmetic unit that multiplies the output Cv value of the Cv function generator 15 and a constant K, and is a flow rate. is output.

Now, the fluid flowing in the pipe 1 is changed by operating the valve lift of the flow control valve 6 by a separately provided control device.

The valve lift detector 14 detects the valve lift of the flow control valve 6 and sends an output signal as an input signal to the Cv function generator 15 to generate a function of the Cv value unique to the valve.

On the other hand, the fluid pressures PUPL on the upstream and downstream sides of the flow control valve 6, which are transmitted to the pressure transducers 9 and 11 via the impulse pipes 8 and 10, are converted into electrical signals and input to the deviation device 12 manually. Deviation device 1
The differential pressure pu -pL obtained in step 2 is subjected to square rooting of its absolute value in a square root calculator 13 and inputted to a 1 multiplier 16, where it is multiplied by the above Cv value and a constant and the flow rate Q is output. Ru.

Conventionally, orifices have been used in flow rate detection devices for the purpose of automatically controlling the flow rate of fluid flowing in piping.

When using an orifice.

Based on the principle of differential pressure detection, it is inevitable that the impulse pipes are installed in close proximity, so when extremely low temperature evaporative liquid fluids are involved, it is difficult to prevent external input, especially at minute flow rates. Heat travels through the impulse tube and reaches the area around the orifice in a concentrated manner. As a result, the generation of bubbles in one local area becomes significant, and the compressibility of the fluid is affected by minute pressure fluctuations in the main pipe, making it easy to cause differential pressure fluctuations. On the other hand, based on the principle that the detected flow rate is proportional to the square root of the differential pressure at the orifice, minute differential pressure fluctuations in a state where the differential pressure is small will be converted into a large flow rate error.

It is inconvenient to use such a detection signal for automatic control.

However, as described above, the device of this embodiment uses the flow regulating valve G itself as a throttling mechanism, and as the opening degree of the flow regulating valve 6 becomes smaller, the differential pressure increases. The flow rate becomes large, and the flow rate becomes small depending mainly on the valve opening degree ('Cv value). Since it is a device that adapts to the reality of this physical phenomenon,
It can have the advantage of eliminating all the drawbacks of flow rate detection when using an orifice as described above.

For example, when the flow control valve 6 is suddenly contracted in the device shown in FIG. 1, the flow rate detected at the orifice 2 exhibits a reverse response as shown by the solid line in FIG.

According to the present invention, improvements are made as shown by the broken line in FIG. In particular, the longer the upstream pipeline is, the more the difference between the two becomes more pronounced, and the effect of the improvement becomes clearer.

Note that the key points that affect the flow rate detection accuracy in the device of this embodiment are the Cv characteristic of the flow rate control valve 6 and its absolute value.
If it is based on recent valve manufacturing and adjustment technology, it is possible to receive a product with sufficient accuracy for practical use, and if it still needs to be corrected to 1%, the set value of the Cv function generator 15 can be adjusted. It can also be easily modified by

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional device, Fig. 2 is an explanatory diagram of a device showing an embodiment of the present invention, Fig. 3 is a diagram showing the relationship between valve lift and Cv value, and Fig. 4 is a diagram showing the characteristics of flow rate detection. Chill with the graph shown. 1: Piping, 6: Flow control valve, 12: Deviation device. 13: Square root calculator, 14: Valve lift detector. 15: Cv function generator, 16: Multiplier. Shoulder 2 Flashes 3 Flashes 4 Continuation of Figure 1 Page 0 Author: Daisaku Hirata, 2-1-1 Niihama, Arai-cho, Takasago City, Mitsubishi Heavy Industries, Ltd., Takasago Works ■Applicant: 3 people Mitsubishi Heavy Industries, Ltd., Chiyoda-ku, Tokyo Marunouchi 2-5-1

Claims (1)

[Scope of Claims] A device for measuring the flow rate of fluid flowing in a flow path constricted by a flow rate control valve, comprising a valve lift detector for detecting the valve lift of the flow rate control valve. A Cv function generator that generates a unique Cv value of the flow rate control valve based on the valve lift, a deviator that measures the differential pressure between the pressure on the upstream and downstream sides of the flow rate control valve, and the deviator. A flow rate detection device comprising: a square root calculator which squares the absolute value of the obtained value; and a multiplier which multiplies the square root calculator by the output of the Cv function generator and a constant.