JP2711133B2 - Vortex flow meter - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a Karman vortex flowmeter for determining a flow rate of a fluid from a cycle of a Karman vortex generated in the fluid by a vortex generator provided in a pipeline. It is.

"Prior art" The following vortex flowmeter is known as a conventional vortex flowmeter.

As described in JP-A-54-69474, a piezoelectric element provided with an alternating stress generated in a vortex generator itself due to Karman vortices generated by a vortex generator provided in a flow path. A Karman vortex flowmeter which measures the period of the Karman vortex from the detected stress and compares the period with the flow velocity of the fluid to determine the flow rate of the fluid.

As described in JP-B-48-17010, utilizing the fact that ultrasonic waves are radiated into a conduit and the propagation time of the ultrasonic waves is changed by Karman vortices (generated by vortex generators in the flow path), A Karman vortex flowmeter which measures the cycle of the Karman vortex and similarly obtains the flow rate.

"Problems to be Solved by the Invention" However, the cycle of the Karman vortex is determined not only by the flow rate of the fluid flowing in the pipe, but also by the flow conditions determined by conditions such as pump specifications, pipe diameters, and valve positions. Therefore, there is a problem that the measurement accuracy is reduced and the reproducibility is deteriorated when the above-mentioned various conditions are changed due to a difference in installation conditions or specification conditions.

The present invention has been proposed in view of the above circumstances, and has as its object to obtain a flowmeter capable of maintaining a predetermined measurement accuracy regardless of a change in flow conditions.

"Means for Solving the Problems" In order to solve the above-mentioned problems, the present invention provides a vortex generator provided in a pipe, wherein the cycle of Karman vortices generated in the fluid is proportional to the flow velocity of the fluid. In a Karman vortex flowmeter that measures the flow rate of a fluid by utilizing the above, a first detector that detects the cycle of the Karman vortex and outputs a Karman vortex cycle signal, and detects a pressure change before and after the vortex generator. A second detector for detecting, a correction signal calculator for determining a flow condition from the pressure signal supplied from the second detector, and outputting a correction signal corresponding to the determination result; A flow rate calculator that calculates a flow rate signal from the Karman vortex period signal supplied from the vessel and a constant and controls the constant by the correction signal.

[Operation] With the above configuration, a change in the flow condition is detected based on the information on the pressure change obtained from the first detector, and the correction signal output in accordance with the change in the condition allows the constant You can change the value.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

Reference numeral 1 in FIG. 1 denotes a pipe line inserted in series into a pipe to be measured. At two points facing each other via the center of the pipe 1,
An ultrasonic transmitter 2 and an ultrasonic receiver 3 are provided, respectively. A vortex generator 4 having a columnar shape intersecting with the flow is provided at a position upstream of the transmitter 2 and the receiver 3 so as to positively generate the Karman vortex 5 in the pipe fluid on the flow side thereafter. Has become.

The supersonic transmitter 2 is driven by a drive signal output from a driving circuit 6 to propagate the ultrasonic waves 7 to the fluid in the tube, and the ultrasonic waves 7 propagated in the fluid in the tube come into contact with the Karman vortex 5. After being phase-modulated, the ultrasonic signal detected by the ultrasonic receiver 3 and loaded with Karman vortex information
Converted to S1.

The ultrasonic signal S1 is input to the Karman vortex period detector 8 together with the drive signal S′1, and is subjected to phase demodulation, so that the Karman vortex signal is extracted and further waveform-shaped. Is supplied to the flow rate calculator 9 as a pulse signal S2 proportional to.

On the other hand, on the upstream side and the downstream side of the vortex generator 4, pressure detectors 10 and 11 for outputting an electric signal corresponding to the pressure of the fluid in the pipe are provided, respectively.
And 11 are converted into pressure signals S3 and S4 by pressure signal converters 12 and 13, respectively, and output from the correction signal calculator 1
Supplied to 4. The correction signal calculator 14 calculates a correction signal S5 based on information such as the pipe pressure, the pulsation component, and the pressure difference before and after the vortex generator obtained from the pressure signals S3 and S4, and supplies the correction signal S5 to the flow rate calculator 9. doing.

Further, the flow rate calculator 9 corrects the Karman vortex cycle pulse signal S2 based on the correction signal S5, and then outputs a signal S6 indicating the flow velocity (flow rate) of the fluid in the pipeline from the corrected Karman vortex cycle. . That is, in the flow rate calculator 9, the supplied pulse S2 and the meter constant (number of pulses / number of pulses /
A) calculating a correction coefficient C to obtain a flow rate signal S6, and controlling the meter constant C based on the correction signal S5 to calculate an accurate flow rate corresponding to a change in flow. I have.

The meter constant C changes as shown in FIG. 2 depending on pump conditions and piping conditions. 3 to 5 show piping systems under conditions corresponding to conditions 1, 2, and 3 in FIG.

◎ Condition 1 A small-capacity pump P1 is used, and a straightening pipe A, a pipe 10D, and a vortex flow meter F having the structure shown in FIG. The flow rate is controlled by a valve V provided on a downstream pipe 20D (20D represents a pipe diameter twice as large as 10D).

◎ Condition 2 A pump P2 having a larger capacity than the pump P1 is used, and the flow rate is controlled by a valve V provided on a pipe indicated by reference numeral 40D (40D is a pipe diameter four times larger than 10D) upstream of the rectifying pipe A. Do.

◎ Condition 3 The flow rate is controlled by using the pump P2 having the same capacity as in Condition 2 and using the valve V provided in the pipe 20D downstream of the rectifier pipe A.

Under each condition, when the characteristic of the meter constant C of the flow meter is obtained while controlling the flow rate by operating the valve V, under the condition 1, as shown in FIG. To rise. In condition 2, the increase is small, and in condition 3, it decreases in reverse. These facts show that even when the same vortex flowmeter is used, the Karman vortex period output at the same flow point is different due to the above-described difference in conditions.

Then, when the state of the pressure in the pipe is measured for each condition by the pressure detectors 10 and 11 provided respectively on the upstream and downstream of the vortex generating column, the pressure, the pulsation component, the upstream and downstream It was found that the pressure information such as the pressure difference was different.

Therefore, the flow conditions are set variously to obtain the meter constant C, and if the pressure is measured under the conditions, the pressure information S2, obtained from the pressure detectors 10, 11 can be obtained.
Based on S3, the correction signal calculator 14 determines which condition (for example, any one of the conditions 1 to 3 in the embodiment), and supplies the result of the determination to the flow calculator 9 as the correction signal S5. A Kalman vortex flowmeter which can always obtain accurate measurement values by setting an appropriate meter constant C in the computing unit 9 (or selecting an optimum meter constant curve stored in advance for each condition). We were able to.

In the above-described embodiment, the method has been described in which the pressure detectors are installed at two locations upstream and downstream of the vortex generator. However, a larger number of pressure sensors may be installed. What is necessary is just to arrange so that the pressure information showing the state of can be obtained.

Further, in the above embodiment, the method of obtaining the signal corresponding to the flow rate by measuring the Karman vortex period using the phase change of the ultrasonic wave has been described.
Adopt a method that uses amplitude change or frequency change, etc.
It is apparent that the present invention can be applied to the case where Karman vortex is detected using a sensor other than the ultrasonic wave, such as a piezoelectric element, a capacitance, or a heat ray.

[Effects of the Invention] As is clear from the above description, according to the present invention, a change in the flow state affecting the generation of Karman vortices can be detected through pressure measurement. This eliminates a change in the Karman vortex period due to a change in conditions or the like, and provides an effect that measurement can be performed with high accuracy and high reproducibility.

[Brief description of the drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a block diagram of a vortex flowmeter, FIG. 2 is a table showing a relationship between a flow rate and a meter constant for each piping condition, and FIGS. Is the condition 1
It is a piping diagram which shows the structure of 3 piping, respectively. DESCRIPTION OF SYMBOLS 1 ... Pipe, 2 ... Transmitter, 3 ... Receiver, 4 ... Vortex generator, 5 ... Karman vortex, 6 ... Drive circuit, 7 ... Ultrasonic, 8 ... Karman vortex frequency detector , 9 ... Flow calculator, 10/11 ... Pressure detector, 12/13 ... Pressure signal calculator, 14 ... Correction signal calculator.

Claims (1)

(57) [Claims] 1. A Karman vortex flowmeter for measuring the flow rate of a fluid by utilizing the fact that the period of a Karman vortex generated in a fluid by a vortex generator disposed in a pipe is proportional to the flow velocity of the fluid. A first detector for detecting a cycle of the Karman vortex and outputting a Karman vortex cycle signal, a second detector for detecting a pressure change before and after the vortex generator, and a second detector. A correction signal calculator for determining a flow condition from the supplied pressure signal and outputting a correction signal corresponding to the determination result; and a flow signal from the Karman vortex period signal and a constant supplied from the first detector. A vortex flowmeter for calculating and controlling the constant by the correction signal.