JPH02280010A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To eliminate a Karman vortex caused by the variation of a condition of a flow such as a pump condition by correcting a pulse signal being proportional to the period of the Karman vortex with a correcting signal for discriminating the condition of the flow. CONSTITUTION:Pressure detectors 10, 11 are provided on the upstream and the downstream of a vortex generating body 4, and their signals are converted to pressure signals S3, S4 by pressure signal converters 12, 13, and supplied to a correcting signal computing element 14. The computing element 14 calculates a correcting signal S5, based on the information of pipe pressure, a pulsating component, etc., obtained from the signals S3, S4 and supplies it to a flow rate computing element 9. The computing element 9 corrects a pulse signal S2 being proportional to the period of the Karman vortex 5 by the correcting signal S5, and thereafter, outputs a signal S6 for showing a pipe flow rate. Therefore, the variation of the period of the Karman vortex caused by the variation of a pump condition, a piping condition, etc., is eliminated, and the measurement can be executed with high accuracy.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a Karman vortex flowmeter that determines the flow rate of a fluid from the period of a Karman vortex generated in a fluid by a vortex generator provided in a pipe. It is.

"Prior Art" The following system is known as a conventional eddy current meter.

■ As described in Japanese Patent Application Laid-Open No. 54-69474, the alternating stress generated in the vortex generator itself due to the Karman vortex generated by the vortex generator installed in the flow path is absorbed by a piezoelectric device installed inside the vortex generator. A Karman vortex flow meter which measures the period of the Karman vortex from the stress detected by an element, and determines the flow rate of the fluid by comparing the period with the flow velocity of the fluid.

■ As stated in Special Publication No. 48-17010,
Ultrasonic waves are radiated into the pipe, and the period of the Karman vortex is measured by utilizing the fact that the propagation time changes due to the Karman vortex (generated by a vortex generator in the flow channel), and the flow rate is similarly measured. A Karman vortex flow meter that was designed to be used.

``Problem to be solved by the invention'' However, the period of the Karman vortex is determined not only by the flow rate of the fluid flowing in the pipe, but also by conditions such as pump specifications, pipe diameter, valve position, etc. Therefore, there is a problem in that the measurement accuracy and reproducibility deteriorate when the various conditions change due to differences in installation conditions or usage conditions.

The present invention was proposed in view of the above circumstances, and an object of the present invention is to obtain a flowmeter that can maintain a predetermined measurement accuracy regardless of changes in flow conditions.

"Means for Solving the Problems" In order to solve the above problems, the present invention provides that the period of the Karman vortex generated in a fluid by a vortex generator disposed in a pipe is proportional to the flow velocity of the fluid. A Karman vortex flow meter that measures the flow rate of a fluid by utilizing this phenomenon includes a first detector that detects the period of the Karman vortex and outputs a Karman vortex period signal, and a first detector that detects the period of the Karman vortex and outputs a Karman vortex period signal; a second detector for detection; a correction signal calculator for determining flow conditions from the pressure signal supplied from the second detector and outputting a correction signal corresponding to the determination result; and the first detection A flow rate calculator is provided which calculates a flow rate signal from a Karman vortex periodic signal and a constant supplied from the device and controls the constant by the correction signal.

"Operation" With the above configuration, a change in flow conditions is detected based on the information on the pressure change obtained from the first detector, and a correction signal output according to the change in conditions is used to adjust the constant. Value can be changed.

"Example" Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

Reference numeral 1 in FIG. 1 indicates a pipe line inserted in series into the piping to be measured. An ultrasonic transmitter 2 and an ultrasonic receiver 3 are provided at two points facing each other across the center of the conduit 1, respectively. A column-shaped vortex generator 4 that intersects with the flow is provided at a position upstream of these transmitters 2 and receivers 3, so as to actively generate a Karman vortex 5 in the fluid in the pipe on the downstream side. It has become.

The ultrasonic transmitter 2 is driven by a drive signal output from a drive circuit 6 to propagate an ultrasonic wave 7 to the fluid in the tube, and the ultrasonic wave 7 propagated in the fluid in the tube comes into contact with the Karman vortex 5. (After being subjected to 1γ phase modulation, it is detected by the ultrasonic receiver 3 and converted into an ultrasonic signal Sl having Karman vortex information.

This ultrasonic signal Sl is manually input to the Karman vortex period detector 8 together with the drive signal S'1, and is phase demodulated to extract a Karman vortex signal, which is further waveform-shaped to obtain the period of the Karman vortex 5. is supplied to the flow rate calculator 9 as a pulse signal S2 proportional to .

On the other hand, pressure detectors 10 and 11 are provided on the upstream and downstream sides of the vortex generator 4, respectively, for outputting electrical signals according to the pressure of the fluid in the pipe. The signal is a pressure signal converter 12.1
3 respectively, the pressure signal S3. Converted to S4,
The signal is supplied to a correction signal calculator 14. Then, in the correction signal calculator 14, the pressure signal S3. A correction signal S5 is calculated based on information such as the pipe internal pressure, pulsation component, and pressure difference before and after the vortex generator obtained from the S/I, and is supplied to the flow rate calculator 9.

Furthermore, after correcting the Karman vortex period pulse signal S2 based on the correction signal S5, the flow rate calculator 9 calculates the flow velocity of the fluid in the pipe (flow ff1) based on the corrected Karman vortex period.
) is output. In other words, the above flow rate calculation 2
'A9 calculates the supplied pulse S2 and a meter constant (the number of pulses/C), and calculates the flow rate signal S.
6, and by controlling the meter constant C based on the correction signal S5, an accurate flow m can be calculated in response to changes in the flow.

The meter constant 1c changes as shown in FIG. 2 depending on the pump conditions and piping conditions. Also, Figures 3 to 5
The figure shows a piping system under conditions corresponding to conditions 1 and 2.3 in FIG.

◎Condition 1 A small-capacity pump p1 is used, and the rectifier pipe A1 piping 10D and the eddy current meter F having the configuration shown in Fig. 1 are installed in series on the discharge side of the pump P1. The flow rate is controlled by a valve V provided on the downstream pipe 20D (20D represents a pipe diameter twice that of the IOD).

◎Condition 2: Use pump P2 with a larger capacity than the above pump Pl,
The flow rate is controlled by a valve (2) installed in the pipe upstream of the rectifier pipe A, indicated by the symbol 40D (40D represents a pipe diameter four times larger than 10I).

◎Condition 3 A pump P2 with the same capacity ↑ as in the case of Condition 2 above is used, and the flow rate is controlled using the valve ■ provided in the downstream piping 20D to the rectifier pipe.

Under each condition, the characteristics of the meter constant C of the current m meter are determined while controlling the flow rate by operating the valve ■. Under condition 1, as the flow rate decreases, the meter constant C increases as shown in Figure 2. rises. Furthermore, under condition 2, the increase becomes smaller, and under condition 3, it decreases. These things are
This shows that even if the same vortex flow meter is used, the Karman vortex period output at point m of the same flow differs due to the difference in conditions as described above.

When the pressure detectors 10 and 11 installed upstream and downstream of the vortex generating column measure the state of the pipe pressure under each condition, the pressure, pulsation component, and It was found that the pressure information such as the pressure difference downstream was different.

Therefore, by setting various flow conditions, the meter constant C
If the pressure is determined and the pressure is measured under that condition, the pressure information s2. obtained from the pressure detection 2710.11 can be obtained. s3, the correction signal calculator 14 determines which condition (for example, any of conditions 1 to 3 in the embodiment) and supplies the determination result to the flow rate calculator 9 as a correction signal S5. By setting an appropriate meter constant C in the calculator 9 (or by selecting the optimal one from a number of meter constant curves prepared in advance for each condition), a Karman vortex flowmeter that always provides accurate measurement values can be created. I was able to make it happen.

In the above embodiment, a method was explained in which pressure detectors are installed at two locations upstream and downstream of the vortex generator, but a larger number may be installed, and in short, the flow that causes the change in the meter constant C It suffices if the arrangement is such that pressure information representing the state can be obtained.

In addition, in the second embodiment, a method was explained in which a signal corresponding to the flow rate is obtained by measuring the Karman vortex period using a phase change of ultrasonic waves, but instead of this method, an amplitude change or a frequency It is clear that the present invention can also be applied to detecting Karman vortices by adopting a method using changes, etc., and using sensors other than ultrasonic waves, such as piezoelectric elements, capacitance, heat rays, etc.

"Effects of the Invention" As is clear from the above explanation, according to the present invention, changes in the flow state that affect the generation of Karman vortices can be detected through pressure measurement. By removing changes in the Karman vortex period due to changes in conditions,
It has the effect of being able to measure with high precision and reproducibility.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention; Fig. 1 is a block diagram of a vortex flow meter, Fig. 2 is a chart showing the relationship between flow rate and meter constant for each piping condition, and Figs. 3 to 5. is condition 1~
3 is a piping diagram showing the configuration of piping in No. 3. FIG. l... Piping, 2... Transmitter, 3...
...Receiver, 4... Vortex generator, 5...
・Karman vortex, 6...drive circuit, 7...ultrasonic wave, 8...karman vortex frequency detector, 9...
...Flow rate calculator, IO・11...Pressure detector,
12・13... Pressure signal calculator, 14...
・Correction signal calculator. Applicant Tokico Co., Ltd.

Claims (1)

[Claims] In a Karman vortex flowmeter that measures 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 that detects the period of the Karman vortex and outputs a Karman vortex periodic signal; a second detector that detects a pressure change before and after the vortex generating body; a correction signal calculator that discriminates flow conditions from the pressure signal generated and outputs a correction signal corresponding to the discrimination result;
A vortex flowmeter comprising: a flow rate calculator that calculates a flow rate signal from a constant and a Karman vortex periodic signal supplied from the detector, and controls the constant using the correction signal.