JPS6329210Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] The present invention relates to a device for detecting the flow rate of fluid flowing in a piping flow path. [Prior Art] When determining the flow rate of fluid flowing in a piping channel, an orifice is usually used. That is, as shown in FIG. 1, an orifice 2 is installed in a pipe 1, and 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 is converted into a flow rate based on a predetermined relationship such as the Reynolds number, and the converter 7 outputs the converted flow rate. [Problems to be Solved by the Invention] When measuring the flow rate of a cryogenically evaporable liquid fluid such as liquid nitrogen using a device constructed in this manner, problems may occur. A problem occurs when the flow control valve 6 installed in the pipe 1 is close to fully closed and there is almost no flow. Although the piping 1 and the impulse pipes 3 and 4 are wrapped with heat insulating material, some amount of heat cannot be avoided. Therefore, when there is almost no flow, the heat input from the impulse pipes 3, 4, etc.
The liquid around the orifice 2 vaporizes and bubbles are generated locally, which often causes the differential pressure transmitted to the differential pressure gauge 5 to fluctuate abnormally. In addition, when measuring flow rate using a throttle mechanism such as orifice 2, the flow rate is proportional to the square root of the differential pressure, but since the opening area of orifice 2 is constant, it is not possible to make the differential pressure particularly large, and the flow rate is small. This results in the use of the same differential pressure. Abnormal fluctuations in pressure due to the generation of bubbles will result in extremely large detection errors, further aggravating the aforementioned problems and impairing the stability and reliability of flow measurement. [Means for Solving the Problems] The present invention eliminates these drawbacks, and the valve opening degree changes continuously from fully closed to fully open as a function of the valve lift, and the flow in the piping flow path is improved. A flow control valve that controls the flow rate of fluid, a valve lift controller that controls the valve lift of the flow control valve, and a compensation circuit that branches the output of the valve lift controller to compensate for the transient response of the flow control valve. , a Cv function generator that generates the unique flow coefficient Cv of the flow control valve based on the valve lift compensated by the same compensation circuit, and the pressure difference between the pressure on the upper and downstream sides near the flow control valve is measured. a square root calculator that squares the absolute value of the value obtained by the deviation device, and a multiplier that multiplies the square root calculator and the output of the Cv function generator and a constant, The purpose of this is to be able to accurately determine the flow rate even when there is almost no flow of cryogenic evaporative liquid fluid, and to make it possible to use it for flow control by adding a compensation circuit. The present invention provides a flow rate detection device that can improve dynamic characteristics. [Operations and Effects] That is, the flow rate detection device according to the present invention eliminates the use of an orifice and uses the flow rate control valve used in the conduit as a throttling mechanism, and the flow rate Q (m) of the fluid flowing through the flow rate control valve is ³ /h) is the flow rate coefficient of the flow rate control valve, Cv is the differential pressure between the upstream and downstream sides of the flow rate control valve, △P (Kg/cm ² ), and the specific gravity of the fluid is Gf.

〔Example〕

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 fluid flows, and a flow control valve 6 for controlling the flow rate is interposed therein, and a pair of impulse pipes 8 and 10 are provided near the upper and downstream sides thereof. 9 and 11 are fluid pressure PU guided by impulse pipes 8 and 10;
This is a pressure transducer for measuring PL, and its output is introduced into a deviation device 12 to detect the differential pressure PU-PL. Reference numeral 13 denotes a square root calculator that squares the absolute value of the differential pressure PU-PL detected by the deviation device 12, and outputs the value √|-| to a multiplier 17, which will be described later. Reference numeral 14 denotes a valve lift controller that gives the flow control valve 6 a valve lift determined by a control device (not shown), and includes a signal converter 19 and a valve operator 20.
The flow rate control valve 6 is operated via. The compensation circuit 15 has a lower limit of the time constant of the approximate first-order delay characteristic of the valve operator 20, and has a time constant of at least 50
This is a compensation circuit that has a function of arbitrarily setting a time constant up to a % larger time constant, and receives the output of the valve lift controller 14 and sends it to the Cv function generator 16. The Cv function generator 16 is based on the valve lift signal of the flow control valve 6 given by the valve lift controller 14, and stores a function between the valve lift and a unique flow coefficient Cv as shown in FIG. 17 is a calculator which multiplies the output √|-| of the square root calculator 13, the output Cv value of the Cv function generator 16, and a constant K, and outputs the flow rate Q. Now, the flow rate Q of the fluid flowing through the pipe 1 is changed by operating the valve lift of the flow rate control valve 6 based on a signal given to the valve lift controller 14 from a separately provided control device. At this time, the valve lift signal compensated for a predetermined time by the compensation circuit 15 is input to the Cv function generator 16, and its Cv value is output almost in synchronization with the flow rate control valve 6, or at a later time, and is multiplied. The signal is sent to the device 17. On the other hand, pressure transducers 9,
The fluid pressures PU and PL on the upstream and downstream sides of the flow control valve 6 that are transmitted to the deviator 11 are converted into electrical signals.
2 is input. Differential pressure PU obtained by deviation device 12
-PL is subjected to the square root of its absolute value in the square root calculator 13, and is inputted to the multiplier 17, where it is multiplied by the Cv value and a constant, and the flow rate Q is output. In a conventional liquid flow rate detection device using an orifice, for example, when the flow rate control valve 6 is rapidly closed, the effect of "water hammer" is strong on the upstream side of the orifice, resulting in a transient reversal of the differential pressure. Since the orifice opening area is constant, the detected flow rate Q increases by about 20% (for about 5 seconds) in the opposite direction as shown by the solid line in Figure 4, a so-called "reverse response".
There will be an error. This error is caused by the "principle of differential pressure detection" in which when the target fluid is extremely low-temperature and evaporative, the impulse tube is installed in close position between the orifice. This becomes more noticeable when intensive flushing occurs, and when the flow rate becomes even lower, it develops into a pulsating error. However, as described above, the device of this embodiment uses the flow rate control valve 6 itself, which is originally provided for the purpose of flow rate control, as a throttling mechanism, and as the opening degree of the flow rate control valve 6 becomes smaller, The differential pressure becomes large, and the flow rate mainly depends on the valve opening, i.e.
It becomes small depending on the Cv value. Since the device is adapted to the actual state of this physical phenomenon, it can have the feature of eliminating all the drawbacks of flow rate detection when using an orifice as described above. Furthermore, since the actual valve lift of the flow rate control valve 6 is not used, and the valve lift command value is compensated by the compensation circuit 15 by corresponding to the time constant of "valve operation delay", there is no need to detect the valve lift. This is particularly effective in cases where it is difficult to install such a detector. Note that if the time constant of the compensation circuit 15 is set larger than the actual operation lag time constant of the valve, the detected flow rate will lag behind the actual one, so if this is used in the feedback control system, there will be a "lead effect" at the beginning of the transient operation. '' and a ``delay effect'' in the latter stage, resulting in the effect of improving the dynamic characteristics of the flow rate control system. It is also effective in alleviating the "water hammer phenomenon." As mentioned above, the greatest feature of the present invention is that the valve has the function of a variable orifice, so differential pressure can be detected stably at small flow rates, eliminating unnecessary water head loss and turbulence in the piping flow path. Since this does not occur, the flow rate can be detected with high precision over the entire range of valve lift movement, even for extremely low-temperature evaporative liquids.Additionally, by adding the compensation circuit, the flow rate control valve 6 has an "advance effect" at the beginning of a transient operation. In the latter stage, it acts as a ``delay effect'' and is effective in improving control stability and mitigating the ``water hammer phenomenon'' in the pipeline.

[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 shows the characteristics of flow rate detection. This is a graph showing. 1...Piping, 6...Flow control valve, 12...Deviator, 13...Square root calculator, 14...Valve lift controller, 15...Compensation circuit, 16...Cv function generator,
17... Multiplier.

Claims (1)

[Scope of utility model registration request] A flow control valve that continuously changes from fully closed to fully open as a function of valve lift to control the flow rate of fluid flowing in a piping flow path, and a valve lift controller that controls the valve lift of the flow control valve. a compensation circuit that branches the output of the valve lift controller to compensate for the transient operation of the flow control valve; and a Cv that generates a unique flow coefficient Cv of the flow control valve based on the valve lift compensated by the compensation circuit. a function generator; a deviation device that measures the differential pressure between upstream and downstream pressures near the flow rate control valve;
A compensation circuit comprising: a square root operator that squares the absolute value of the value obtained by the deviator; and a multiplier that multiplies the square root operator and the output of the Cv function generator and a constant. Equipped with a flow rate detection device.